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Applied Catalysis B, Environmental (v.111-112, #)

Contents Continued (pp. iii-iv).

Editorial Board (pp. co2).

Editorial Board (pp. i).

Outside Back Cover (pp. co4).

Gas-phase photocatalytic activity of nanostructured titanium dioxide from flame aerosol synthesis by Svetlana Jõks; Deniss Klauson; Marina Krichevskaya; Sergei Preis; Fei Qi; Alfred Weber; Anna Moiseev; Joachim Deubener (pp. 1-9).

Display Omitted► Superior photocatalytic performance of flame synthesized titania compared to P25. ► Anatase crystallites of reduced size were more sensitive to increased temperature. ► Slower deactivation and faster restoration of flame synthesized catalyst.The experimental evaluation of gas-phase photocatalytic activity of a TiO₂ nanopowder synthesized in a flame aerosol reactor was carried out in photocatalytic oxidation (PCO) of volatile organic compounds (VOCs). The nanopowder has an average particle size of 13nm, anatase content 97wt.% and the specific surface area of 102m²g⁻¹. The performance was compared to the benchmark photocatalyst, the commercial pyrogenic titania P25, Evonik, with the average particle size of 21nm. The full-factorial experiments were carried out varying contact times, concentrations of pollutants and temperatures in continuous gas-flow mode degrading aliphatic acrylonitrile (AN) and aromatic toluene. Higher conversions at more stable performance were observed for the flame aerosol synthesized photocatalyst in degradation of both pollutants. While the primary particle size and specific surface area present the apparent reasons for improved PCO performance in adsorbable AN, these parameters cannot do the same in oxidation of poorly adsorbable toluene: the superior generation of hydroxyl radicals and, therefore, advanced oxidative activity are proposed as explanation. The intense dehydration of reduced size anatase crystallites at elevated temperature (130°C) presumably resulted in decreased OH-radicals production along with the improved desorption of HCN, the PCO by-product of AN. The safe performance is thus requiring lower operational temperatures. Slower deactivation and faster restoration of catalytic activity of flame aerosol synthesized catalyst under UV-A-radiation are discussed.

Keywords: Flame aerosol synthesis; Photocatalytic activity; Titanium dioxide; Air pollution; Volatile organic compounds

Effect of gallium loading on the hydrodesulfurization activity of unsupported Ga₂S₃/WS₂ catalysts by T.A. Zepeda; B. Pawelec; J.N. Díaz de León; J.A. de los Reyes; A. Olivas (pp. 10-19).

The gallium addition has a strong effect on the morphology of the tungsten sulfide phase by modifying the coordinately unsaturated sites (CUS) of the WS₂ phase and total catalyst acidity. Ga-loaded catalysts showed an increase of HDS activity via hydrogenation (HYD) pathway and additional DBT cracking.Display Omitted► Ga addition has a strong effect on CU sites of the WS₂ phase and total catalyst acidity. ► Ga incorporation enhanced the HYD route of HDS of DBT reaction and DBT cracking. ► Ga addition increment the amount of “corner sites” on the WS₂ slabs.The effect of gallium incorporation into unsupported tungsten sulfide catalysts was investigated in dibenzothiophene (DBT) hydrodesulfurization (HDS) reaction. The Ga/WS₂ catalysts with variable gallium loadings (0.5–2.5wt%) were prepared by decomposition of W-thiosalt followed by impregnation with the Ga salt precursor. The samples were characterized by a variety of techniques: ICP-AES, N₂ adsorption–desorption at −196°C, XRD, SEM, XPS, FTIR of CO chemisorbed and TPD-NH₃. The last two techniques showed that gallium addition has a strong effect on the morphology of the tungsten sulfide phase by modifying the coordinately unsaturated sites (CUS) of the WS₂ phase and total catalyst acidity. The HDS of DBT reaction ( T=320°C,PH2=5.5MPa) was found to proceed through two main parallel pathways: hydrogenation (HYD) and direct desulfurization (DDS), the latter being the main reaction route. With respect to Ga-free WS₂ sample, all Ga-loaded catalysts showed an increase of HDS activity via hydrogenation (HYD) pathway and additional DBT cracking. The 1.5% Ga/WS₂ catalyst was the most active among the catalysts studied. On the basis of the catalyst structure–activity relationship, this was linked to a homogeneous distribution of Ga species on the surface of WS₂ (SEM), the largest amount of acid sites (from TPD-NH₃) and the largest amount of “corner sites” on the WS₂ slabs determined by FTIR-CO. For the Ga-containing catalysts, an increase of DBT transformation via HYD route was explained in terms of the formation of new CUS sites on WS₂ phase as well as to an increase of the catalyst acidity. Acidity is a key requirement influencing on DBT cracking.

Keywords: Unsupported WS; ₂; catalysts; Hydroprocessing catalysts; Hydrodesulfurization; Gallium; Hydrocracking; DBT; Tungsten catalysts

The influence of sulfur dioxide and water on the performance of a marine SCR catalyst by Mathias Magnusson; Erik Fridell; Hanna H. Ingelsten (pp. 20-26).

Display Omitted► Investigates the influence of SO₂ and H₂O on the performance of a marine SCR catalyst. ► SO₂, in the absence of H₂O, promotes NO_x reduction, NH₃ conversion and N₂O formation. ► H₂O, in the absence of SO₂, decreases NO_x reduction and inhibits N₂O formation. ► In the presence of both SO₂ and H₂O the activity for NO_x reduction decreases.This study investigates how sulfur affects the NO_x reduction activity over a commercial vanadium based urea-SCR catalyst for marine applications, especially at low temperatures, and in combination with H₂O. The addition of SO₂ in the absence of H₂O promotes the NO_x reduction at 350°C, while the addition of H₂O, in the absence of SO₂, gives rise to a decrease in the NO_x reduction and also an inhibition of the N₂O formation. The same trends are observed at transient temperatures, but no promotional effect by SO₂ is seen at temperatures below 230°C. Further, long term effects of SO₂ and H₂O were investigated and the NO_x reduction remains stable, also after long term exposure of SO₂. The ammonia desorption is investigated using temperature programmed desorption (TPD) experiments, both in the presence and in the absence of SO₂. In general in the presence of both H₂O and SO₂ the catalyst does not show any sign of deactivation at temperatures above 300°C and fairly low space velocities (below 12,200h⁻¹). However, at lower temperatures (250°C) and/or higher space velocities the catalytic performance for NO_x reduction decreases with time.

Keywords: Urea-SCR catalyst; NO; _x; reduction; Marine applications; Sulfur dioxide; Water

Comparative study of Rh–MoO_x and Rh–ReO_x supported on SiO₂ for the hydrogenolysis of ethers and polyols by Shuichi Koso; Hideo Watanabe; Kazu Okumura; Yoshinao Nakagawa; Keiichi Tomishige (pp. 27-37).

Display Omitted► Rh-MO_x/SiO₂ (M=Mo, Re; M/Rh=0.13) showed high hydrogenolysis activity. ► All the Mo and Re species interacts with Rh metal surface. ► Mo and Re species have isolated and 2-D structure, respectively. ► Different reactivity is due to the difference in the local structure of Mo and Re.Rh–MO_x/SiO₂ (M=Mo or Re) catalysts shows the high activity of the hydrogenolysis of C–O bond in the substrates with CH₂OH group such as tetrahydrofurfuryl alcohol, various diols and their ethers. Characterization results suggest the catalyst structure were isolated MoO_x species and small ReO_x cluster with low valence attached on the surface of Rh metal particles. It is characteristic that the reactivity of the C–O bond in the –O–C–C–CH₂OH is higher than that in the –O–C–CH₂OH over Rh–MoO_x/SiO₂, and Rh–ReO_x/SiO₂ has the opposite tendency to Rh–MoO_x/SiO₂. The difference in the regioselectivity of the hydrogenolysis over Rh–MoO_x/SiO₂ and Rh–ReO_x/SiO₂ can be related to the different structure of isolated MoO_x species and small ReO_x clusters.

Keywords: Metal–oxide interaction; Low valent Mo; Low valent Re; Hydrogenolysis; Regioselectivity

Synthesis of mesoporous nitrogen–tungsten co-doped TiO₂ photocatalysts with high visible light activity by Sapanbir S. Thind; Guosheng Wu; Aicheng Chen (pp. 38-45).

.Display Omitted► Synthesis N,W co-doped TiO₂ photocatalysts via a facile solution combustion method. ► The fabricated N,W–TiO₂ nanomaterials possess a mesoporous structure and high surface area. ► N,W co-doping significantly narrows the TiO₂ energy band gap. ► The N,W–TiO₂ photocatalyst exhibit superb visible light response.Mesoporous N,W co-doped TiO₂ photocatalysts that contained various percentages of atomic tungsten dopant levels were synthesized by a facile solution combustion method which utilized urea as a nitrogen source and sodium tungstate as a tungsten source. The prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), N₂ physisorption, UV–vis absorbance spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results reveal that the synthesized N and W co-doped TiO₂ nanomaterials have high surface areas and mesoporous structures. In addition, the co-doping significantly narrows the band gap (∼2.7eV) that is responsible for the high visible light response of these samples in comparison to that of pure anatase TiO₂ (∼3.2eV). The photocatalytic activity of the prepared samples was evaluated on the basis of the photodegradation rate of Rhodamine B under visible light ( λ>420). It was found that the mesoporous N,W co-doped TiO₂ nanomaterials fabricated in this study exhibited high visible light activity. This significant improvement in photocatalytic activity may be attributed to the synergistic effect of the red shift in absorption combined with a high surface area.

Keywords: Photocatalysis; Mesoporous; TiO; ₂; N,W co-doping; Visible light activity

Nanometric palladium confined in mesoporous silica as efficient catalysts for toluene oxidation at low temperature by Chi He; Fuwang Zhang; Lin Yue; Xuesong Shang; Jinsheng Chen; Zhengping Hao (pp. 46-57).

.Display Omitted► Short column mesoporous silica with controllable acidity, expanded microporosity and 3-D micro/mesoporous composite structure. ► Both catalysts combined promoted accessibility and enhanced acid strength. ► Highly dispersed Pd-confined catalysts with improved hydrothermal stability. ► Catalyst with high turnover frequency and superior low temperature efficiency.Short column SBA-15 supported Pd mesoporous catalysts with controllable acidity and expanded microporosity were firstly prepared through a simple “two-solvents” approach. The catalytic performances of the synthesized catalysts were evaluated for toluene oxidation. The characterization results reveal that Al atoms prefer to be tetrahedrally coordinated in the framework of the synthesized materials, and the acid sites can significantly promote Pd particle dispersion and metallic Pd oxidation due to their electrophilic characters. The Pd-confined catalysts possess high toluene turnover frequencies and toluene can be totally converted to CO₂ and H₂O below 210°C. The oxidation reaction can be suppressed by water vapor due to the formation of inactive Pd-hydroxides, and the synthesized catalyst has a good hydrothermal stability and high tolerance to moisture. Both the specific surface area and the toluene adsorption/desorption property are not the main factors determining the catalytic activity. Overall, the toluene oxidation performance is closely related to the support microporosity and acidity, the Pd dispersion and the CO₂ desorption capability.

Keywords: Mesoporous silica; Two-solvents technique; Pd-confined; Controllable acidity; Volatile organic compounds

Mechanistic investigation of hydrothermal aging of Cu-Beta for ammonia SCR by Norman Wilken; Kurnia Wijayanti; Krishna Kamasamudram; Neal W. Currier; Ramya Vedaiyan; Aleksey Yezerets; Louise Olsson (pp. 58-66).

NH₃ SCR over a Cu-BEA catalyst was studied after hydrothermal aging between 500 and 900°C. The figure shows one case with 50% NO₂/NO_x ratio.Display Omitted► The hydrothermal aging behavior of a Cu-BEA model catalyst was studied. ► No significant change of the physical structure could be observed using XRD for a sample aged between 500 and 800°C. ► We observe a decrease in Cu⁺ using XPS, which could be one of the deactivation mechanisms. ► TPD and calorimeter experiments show a trend towards less strongly bound ammonia with increasing aging temperatures. ► Different reactions show different trends during aging. Thus it is possible that there are different active sites.The selective catalytic reduction of NO_x with NH₃ over a Cu-BEA catalyst was studied after hydrothermal aging between 500 and 900°C. The corresponding catalyst was characterized using XPS and XRD techniques in the aging interval of 500, 700 and 800°C. No structural changes during the aging process were observed. However, the oxidation state of copper changed during aging and more Cu²⁺ was formed. We suggest that one of the deactivation mechanisms is the decrease of the Cu⁺ species. The NO oxidation and NH₃ oxidation activity was decreased with increasing aging temperature. Further, we observed that the ammonia oxidation was decreased faster compared to the SCR reactions at low aging temperatures. The experiments from the calorimeter as well as from the ammonia TPD investigations indicate a trend towards more weakly bound ammonia with higher aging temperatures. From the results of the SCR experiments using different NO₂/NO_x ratios and ammonia oxidation experiments we suggest that most of the N₂O is coming from side reactions of the SCR mechanism and not from reactions between NH₃ and O₂ alone. Interestingly, we observe that after the 900°C aging a quite large activity remained for the case with 75% NO₂/NO_x ratio. The N₂O production shows a maximum at 200°C, but increases again at higher temperatures. However, the N₂O formed at low temperature is decreased after hydrothermal aging while the high temperature N₂O is increased. We propose that the different reactions examined in this work do not all occur on the same type of sites, since we observe different aging trends for some of the reactions.

Keywords: Ammonia; SCR; Aging; Hydrothermal; Oxidation; Calorimeter; DSC; Zeolite; Beta; Heat of adsorption; XPS; XRD

Selective catalytic reduction of NO_x on combined Fe- and Cu-zeolite monolithic catalysts: Sequential and dual layer configurations by Pranit S. Metkar; Michael P. Harold; Vemuri Balakotaiah (pp. 67-80).

Display Omitted► Dual layer SCR catalyst comprising a thin Fe-zeolite layer on top of a thick Cu-zeolite layer exhibits improved activity. ► Dual layer Fe/Cu catalyst expands temperature window of high NO_x conversion for standard and fast SCR. ► Performance of a dual layer catalyst is comparable with series arrangement of Fe- and Cu-zeolite bricks. ► Proven existence of mass transfer limitations means double layer catalyst is superior configuration.Iron and copper-based zeolites are effective catalysts for the lean selective catalytic reduction (SCR) of NO_x with NH₃. Cu-zeolites are more active at lower temperatures (≤350°C) while Fe-zeolites are more active at higher temperatures (≥400°C). The effectiveness of a catalytic system comprising Fe- and Cu-based zeolites was examined for the standard (NO+O₂+NH₃) and fast (NO+NO₂+NH₃) SCR reactions. Experiments carried out with in-house and commercial Fe- and Cu-zeolite monoliths of varying lengths quantified their relative SCR activities. The commercial Cu-zeolite achieved complete NO_x conversion for the standard SCR at 250°C while the commercial Fe-zeolite achieved high NO_x conversion at higher temperatures (≥400°C) where it out-performed the Cu-zeolite. Subsequently, three configurations of combined Fe and Cu-zeolite catalysts were compared:•“Sequential brick” catalyst comprising Fe-zeolite and Cu-zeolite monolith.•“Mixed washcoat” catalyst comprising a washcoat layer having equal mass fractions of Fe- and Cu-zeolites.•“Dual layer” catalyst comprising monolith coated with individual layers of Fe- and Cu-zeolites of different thicknesses and mass fractions.The sequential brick design with Fe-zeolite brick followed by a Cu-zeolite brick gave a higher conversion than the Cu/Fe sequence of equal loadings with the Fe(33%)/Cu(67%) achieving the highest NO_x conversion over a wide range of temperatures. The mixed washcoat catalyst achieved NO_x conversion that was nearly an average of the individual Fe-only and Cu-only catalysts. The dual layer catalyst with a thin Fe-zeolite (33% of the total washcoat loading) layer on top of a thicker Cu-zeolite layer (67%) resulted in very high NO_x removal efficiencies over a wide temperature range for both the standard and fast SCR reactions. The performance of this dual-layer system was comparable to the series arrangement of Fe and Cu-bricks. The Cu-zeolite on Fe-zeolite dual layer catalyst was not nearly as effective for the same loadings. The Fe/Cu dual layer catalyst also exhibited superior performance for the fast SCR reaction. The results are interpreted in terms of the activities of each catalyst for SCR and ammonia oxidation. An assessment of the extent of washcoat diffusion limitations shows that the dual layer configuration is superior to the sequential brick configuration. The existence of an optimal loading distribution of the Fe- and Cu-zeolite catalysts as well as other intangible benefits of the dual layer SCR catalyst are discussed.

Keywords: Selective catalytic reduction; Standard SCR; Fast SCR; Ammonia oxidation; Dual layer catalysts; Fe-zeolite; Cu-zeolite; Fe; Cu; ZSM-5; Monolith

Supported gold nanoparticle catalysts for wet peroxide oxidation by A. Quintanilla; S. García-Rodríguez; C.M. Domínguez; S. Blasco; J.A. Casas; J.J. Rodriguez (pp. 81-89).

.Display Omitted► Wet peroxide oxidation is a gold size and support dependent reaction. ► Particle sizes ≤3nm and supports with high adsorption capacity are beneficial for gold activity. ► Gold improves the selectivity towards mineralization. ► The process is more efficient for organic pollutants with affinity towards gold. ► The oxidation process occurs on the gold surface as well as in the liquid phase.Supported gold nanoparticles are of promising interest in wet hydrogen peroxide oxidation processes due to their efficient hydrogen peroxide consumption and adequate stability. Here, the origin of the catalytic properties of gold in this environmental process is explored by analyzing the influence of the support and the particle size on the activity of supported gold nanoparticles along with the influence of the nature of the target pollutant on the gold reactivity. The reaction mechanism for the oxidation of phenol with activated carbon-supported gold nanoparticles is proposed and the selectivity evaluated. A reaction pathway has been also proposed.The results demonstrate that wet peroxide oxidation is a support and gold size dependent reaction. Activated carbon is the preferable candidate versus TiO₂ and Fe₂O₃ supports and small gold nanoparticles, desirably lower than 3nm, show the highest TOF values. Supports showing adsorption capacity towards the target pollutant contribute to a more efficient use of hydrogen peroxide and, improve the TOF values for the oxidation and mineralization. Organic pollutants forming intermediate complexes with gold, viz. alcohols, are more efficiently oxidized. The inclusion of gold improves substantially the selectivity towards mineralization with respect to the bare activated carbon.

Keywords: Gold; Nanoparticle; Hydrogen peroxide; Catalytic wet oxidation; Oxidation pathway

The selective catalytic reduction of N₂O with CH₄ on Na-MOR and Na-MFI exchanged with copper, cobalt or manganese by Maria Cristina Campa; Valerio Indovina; Daniela Pietrogiacomi (pp. 90-95).

Display Omitted► Cu-, Co- and Mn-zeolites as catalysts for the SCR of N₂O with CH₄. ► Cu- and Co-zeolites are selective for the SCR of N₂O with CH₄. ► Mn-zeolites are not selective for the SCR of N₂O with CH₄. ► In the SCR of N₂O with CH₄ on Cu- and Co-zeolites, no CO formed.Cu-MOR, Cu-MFI, Co-MOR, Co-MFI and Mn-MFI were prepared by ion-exchange of Na-MOR or Na-MFI. On all samples, the catalytic activity for N₂O decomposition, CH₄+N₂O, CH₄+O₂, and for the selective catalytic reduction (SCR) of N₂O in the presence of O₂ was studied in a flow apparatus with GC analysis of reactants and products.Extensively exchanged Cu-MOR and Cu-MFI were active for N₂O decomposition. Cu-MOR and Cu-MFI exchanged at about 20% were much less active. All Co-MOR and Co-MFI catalysts, irrespective of the exchange-extent, were active for the same reaction. Mn-MFI was nearly inactive up to 773K. All catalysts were active for CH₄+N₂O. Cu-MOR and Cu-MFI were active for CH₄+O₂, whereas Co-MOR, Co-MFI and Mn-MFI were much less active for this reaction. Irrespective of the exchange extent, Cu-MOR, Cu-MFI, Co-MOR, and Co-MFI were active for the SCR of N₂O with CH₄. Conversely, Mn-MFI was not active for this reaction. Turnover frequency was slightly higher for the various reactions on Me-MFI (Me=Cu or Co) than for the corresponding reactions on Me-MOR.We conclude that on Cu- and Co-zeolites, the SCR of N₂O with CH₄ consists of two nearly independent reactions: CH₄+N₂O prevails at high temperature (673–773K), and CH₄+O₂ at lower temperature. The two reactions involve different catalytically active oxygen species: CH₄+O₂ involves a molecular form, and CH₄+N₂O a monoatomic form, arising from N₂O. Because Co-MOR and Co-MFI are also active for the SCR of NO_x, we suggest that these materials are promising catalysts for the simultaneous SCR of N₂O and NO_x with CH₄.

Keywords: N; ₂; O SCR with CH; ₄; Cu-MOR; Cu-MFI; Co-MOR; Co-MFI; Mn-MFI

Catalytic and redox properties of bimetallic Cu–Ni systems combined with CeO₂ or Gd-doped CeO₂ for methane oxidation and decomposition by A. Hornés; P. Bera; M. Fernández-García; A. Guerrero-Ruiz; A. Martínez-Arias (pp. 96-105).

. A multitechnique approach is employed to identify active sites involved in methane oxidation and decomposition processes over catalysts of Cu–Ni combined with CeO₂ or Gd-doped CeO₂ during the course of CH₄-TPR tests.Display Omitted► Redox/catalytic correlations for CH₄ oxidation/decomposition during CH₄-TPR over Cu–Ni/CeO₂ vs. CGO catalysts are established. ► A promoting effect of Gd on CH₄ oxidation by copper or nickel oxide phases in the catalysts is revealed. ► CH₄ decomposition is produced over Cu–Ni alloys formed during the course of interaction of the oxidised catalysts with CH₄. ► Oxygen species from fluorite CeO₂ or CGO phases of the catalysts basically intervene in syngas formation.Two catalysts combining Cu–Ni with CeO₂ and Gd-doped CeO₂, respectively, are comparatively examined with respect to redox and catalytic properties towards interaction with CH₄. For this, catalysts in oxidised starting states are explored by means of CH₄-TPR tests up to 973K. Characterization of initial and final states of the catalysts is accomplished by means of XRD, Raman spectroscopy and EXAFS while carbon deposits formed during interaction with CH₄ are examined by TPO, Raman spectroscopy and SEM–EDX. Oxygen handling characteristics of the catalysts are examined by means of oxygen isotopic exchange experiments. In turn, redox changes produced during the course of CH₄-TPR tests are explored by operando-XANES. Methane oxidation or decomposition processes are observed as a function of redox state of the catalysts and sites involved in each of the processes are identified on the basis of the multitechnique approach employed.

Keywords: SOFC anode; Methane direct oxidation; Methane decomposition; Copper; Nickel; CeO; ₂; CGO

NO/NO₂/N₂O–NH₃ SCR reactions over a commercial Fe-zeolite catalyst for diesel exhaust aftertreatment: Intrinsic kinetics and monolith converter modelling by Massimo Colombo; Isabella Nova; Enrico Tronconi; Volker Schmeißer; Brigitte Bandl-Konrad; Lisa Zimmermann (pp. 106-118).

Display Omitted► Systematic investigation of NO/NO₂/N₂O–NH₃ SCR reactions over commercial Fe-zeolite. ► N₂O reactivity related to its NO-assisted decomposition and to its SCR with NH₃. ► Global kinetic model developed to fully describe the NO/NO₂/N₂O–NH₃ SCR reactions. ► First SCR model accounting also for N₂O decomposition/reactivity. ► Dynamic 1D+1D model of SCR monolithic converters accounting for mass transfer effects.We present a systematic kinetic investigation of the full NO/NO₂/N₂O–NH₃ SCR reacting system performed over a commercial Fe-promoted zeolite catalyst in the form of powder in a representative temperature range (150–550°C) at high space velocities. The well-known reactions of the NO/NO₂–NH₃ SCR system, namely NH₃ adsorption, NH₃ and NO oxidation, standard-, fast- and NO₂-SCR reactions, ammonium nitrate formation, and N₂O formation are considered. In addition, dedicated runs with N₂O added to the feed stream showed that two more reactions, namely N₂O reduction by NO (N₂O+NO→N₂+NO₂) and N₂O reduction by NH₃ (2NH₃+3N₂O→4N₂+3H₂O) become significant at T>330°C and need to be considered for kinetic modelling.The kinetic runs were fitted by multiresponse nonlinear regression to obtain estimates of the intrinsic rate parameters. Such parameters, as well as the relevant geometrical and morphological catalyst properties, were then successfully used to simulate on a purely predictive basis additional transient SCR runs performed over core honeycomb samples of the same Fe-zeolite catalyst, revealing modest effects of mass transfer limitations.In comparison with other published SCR kinetic models, the model herein developed accounts also for the N₂O reactivity with NO and NH₃, which is shown to be an important feature in order to accurately reproduce high-T operation of SCR converters based on Fe-zeolite catalysts.

Keywords: Urea SCR; Standard SCR; Fast SCR; NO; ₂; SCR; N; ₂; O decomposition; N; ₂; O reactivity; Zeolite catalysts; Diesel exhaust aftertreatment

Preparation and characterization of Ag-doped crystalline titania for photocatalysis applications by S. Krejčíková; L. Matějová; K. Kočí; L. Obalová; Z. Matěj; L. Čapek; O. Šolcová (pp. 119-125).

Display Omitted► Silver presence suppressed the grow of titania crystals in dependence on Ag content. ► Absorption spectra for Ag doped TiO₂ catalysts are shifted into the visible region. ► Positive effect of silver doping on photocatalytic efficiency was confirmed. ► Degradation of 4-chlorophenol over prepared catalyst was successful at 25°C, pH 7.Five pure and silver-enriched TiO₂ catalysts with various Ag loading (0–5.2wt.%) were prepared by the sol–gel technique from nonionic surfactant Triton X-114, cyclohexane, water (or water solution of AgNO₃) and metal precursor. Calcination at 400°C for 4h was applied to convert prepared gels to pure anatase crystalline powders. Effects of silver doping on titanium photocatalyst properties were evaluated by nitrogen physical adsorption, X-ray diffraction, elemental analysis, transmission electron microscopy, Raman spectroscopy, TGA analysis and UV–vis spectroscopy.Two“green” photocatalytic reactions were chosen for photocatalytic experiments: photocatalytic reduction of CO₂ and photocatalytic oxidation of 4-chlorophenol (4-CP) water solution. Both photocatalytic reactions were carried at mild conditions (room temperature and ambient pressure or pH 7). The activity of titania catalysts for photocatalytic reduction of CO₂ was evaluated individually with respect to various UV lamps (254 and 365nm). The UV lamp with wavelength in the range 250–420 with highest maxima at 254 and 365nm was used for photocatalytic oxidation of 4-CP. The dependence of the photocatalytic activity on increase of Ag content was evaluated for both reactions and compared with the photocatalytic activity of Degussa catalyst P25.

Keywords: Silver; TiO; ₂; CO; ₂; reduction; Oxidation; Photocatalysis

Enhancing visible-light-induced photocatalytic activity by coupling with wide-band-gap semiconductor: A case study on Bi₂WO₆/TiO₂ by Jiehui Xu; Wenzhong Wang; Songmei Sun; Lu Wang (pp. 126-132).

.Display Omitted► Bi₂WO₆/TiO₂ photocatalyst with enhanced activity was obtained via a facile one-step hydrothermal process. ► The excellent visible-light activity can be induced by household fluorescent lamp. ► The coupling effect was investigated by PL and EIS with possible mechanism approached.The composites of different semiconductors based on the nanoscale coupling effect for photocatalytic application has been a challenging yet very important research topic. Bi₂WO₆ and TiO₂, the two most extensively studied photocatalysts, were successfully coupled via a facile one-step hydrothermal process. The as-prepared Bi₂WO₆/TiO₂ possessed enhanced visible-light-induced activity in photocatalytic degradation of contaminants in aqueous/gaseous phases compared with those of the sole Bi₂WO₆ or TiO₂. The versatile Bi₂WO₆/TiO₂ photocatalyst also exhibited long-time recyclable ability for the contaminants degradation under visible irradiation ( λ>420nm) of Xenon lamp or household fluorescent lamp. The photoluminescence and electrochemical impedance spectroscopy are both adopted to analyze the physical properties of the photogenerated carriers and it was found that the separation of photogenerated carriers of Bi₂WO₆ has been largely promoted after being coupled with wide-band-gap semiconductor TiO₂. This work could be extended to the design of other composite photocatalyst with the purpose of enhancing activity by coupling suitable wide and narrow band-gap semiconductors, which is inspiring for the practical environmental purification.

Keywords: Bi; ₂; WO; ₆; /TiO; ₂; Photocatalysis; Visible-light; High activity

Adsorption of thiophene and dibenzothiophene on highly dispersed Cu/ZrO₂ adsorbents by P. Baeza; G. Aguila; G. Vargas; J. Ojeda; P. Araya (pp. 133-140).

Display Omitted► ZrO₂ supported Cu adsorbents of thiophene and dibenzothiophene were used for a “deep desulfurization”. ► Different calcination temperatures were used in order to obtain ZrO₂ supports with different specific surface areas. ► Cu/ZrO₂ adsorbents have higher adsorption capacity when the support has a greater specific surface area. ► ZrO₂ with high specific surface area allows a greater dispersion of copper, and therefore a higher adsorption capacity.The effect of surface area of copper/zirconia adsorbents on the adsorption of thiophene (T) and dibenzothiophene (DBT) was studied. Adsorbents were prepared with different loads of copper (1–6%), using as support zirconias with different surface areas, obtained by varying the calcination temperature. Lower calcination temperatures allowed obtaining zirconias with higher surface area, but lower crystallinity. The characterization results showed that high surface area zirconias have greater copper dispersion capacity, being the zirconia calcined at the lower temperature, the only able to completely disperse a load of 6% Cu, i.e., Z-300 surface has only highly dispersed copper species, while zirconias with higher calcination temperature have also bulk CuO species. The adsorption capacity of T or DBT on Cu/ZrO₂ increased with copper content, reaching a maximum, which coincides remarkably with the zirconia dispersion capacity. This result indicates that dispersed copper species, in Cu¹⁺ state, are responsible for the adsorption of these sulfur organic compounds. Therefore the best adsorption capacities were obtained in adsorbents with high content of such copper species, and these adsorbent can be prepared with high surface area ZrO₂, that is with high dispersion capacity of copper.

Keywords: Adsorption; Copper; Zirconia; Thiophene; Dibenzothiophene

Effect of Ce and La on the structure and activity of MnO_x catalyst in catalytic combustion of chlorobenzene by Yu Dai; Xingyi Wang; Qiguang Dai; Dao Li (pp. 141-149).

.Display Omitted► The interface between MnO_x and MnCeO_x is highly active for CB combustion. ► The addition of La can promote the thermal stability of MnCeO_x solid solution. ► The active oxygen enhances the removal of Cl species adsorbed on Mn-based catalysts.Mn-based oxide-mixed catalysts modified with Ce and La, which were prepared by complexation method, were tested in the catalytic combustion of chlorobenzene (CB) as a model of chlorinated aromatics. The characterization by XRD, XPS, TPR and Raman shows that the addition of Ce makes a large portion of Mn species enter CeO₂ fluorite, leading to the formation of MnCeO_x solid solution. The structure to be composed of MnO_x and MnCeO_x solid solution is highly active for CB oxidation due to the presence of a large amount of active oxygen species. The addition of La can promote the thermal stability of MnCeO_x solid solution during calcination up to 750°C, and accordingly the catalyst presents high activity. The study on reaction kinetics shows zero order on CB concentration in the presence of the catalysts except for MnCe-550, indicating that adsorption strength of Cl species produced during the reaction is critical to CB combustion because the adsorbed Cl species can decrease the reducibility of Mn species, thus the mobility of oxygen. Nevertheless, high activity, good selectivity and desired stability were observed over MnCeLa catalysts at 350°C.

Keywords: Chlorobenzene; Catalytic combustion; Cl adsorption; Thermal stability; MnCeO; _x; solid solution

TiO₂ mediated heterogeneous photocatalytic degradation of moxifloxacin: Operational variables and scavenger study by Xander Van Doorslaer; Philippe M. Heynderickx; Kristof Demeestere; Kevin Debevere; Herman Van Langenhove; Jo Dewulf (pp. 150-156).

Display Omitted► Different operational variables are studied for the photocatalytic degradation of MOX. ► A new approach in calculating initial degradation rates is applied. ► Relative contributions of reactive species are determined using scavengers.UV-A (485μWcm⁻²) TiO₂-P25 mediated heterogeneous photocatalysis is investigated as an advanced oxidation technology for the removal of the fluoroquinolone (FQ) antibiotic moxifloxacin (MOX) in aqueous solution. The goal of this work is twofold. First, the degradation kinetics are investigated by changing operational conditions during the degradation reaction. The effect of the initial MOX concentration (12.5–124.6μmolL⁻¹), catalyst concentration (0.25–8.00gL⁻¹), changing the oxygen concentration (0%, 20%, 100%) in the inlet gas flow (60mLmin⁻¹) and temperature (278–338K) on the photocatalytic degradation rate is investigated. An optimal MOX degradation is attained at a catalyst concentration of 5gL⁻¹, 298K and air sparging at 60mLmin⁻¹ resulting in an initial degradation rate of 16.2±0.3μmolL⁻¹min⁻¹ and a half-life time of t_1/2=1.6min.Secondly, the aim is to gain a deeper insight of the photocatalytic degradation mechanism of MOX. Therefore an estimation of the participation of the different reactive species during the photocatalytic degradation of MOX is done using two scavengers in different concentrations. The role of hydroxyl radicals is monitored using isopropanol, and the participation of oxidative holes in the reaction mechanism is evaluated by the addition of iodine anions. The scavenger study indicates that holes are the dominant reactive species, contributing up to 63%, and that hydroxyl radicals participate for about 24% in the photocatalytic degradation of MOX. Reactive oxygen species created by conduction band electrons are probably of lower importance, <13%, during the photocatalytic degradation reaction of MOX.

Keywords: Abbreviations; AOP; advanced oxidation process; CB; conduction band; DNA; desoxyribonucleine acid; DP; degradation product; FQ; fluoroquinolone; HPLC; high performance liquid chromatography; ISO; isopropanol; KI; potassium iodide; L; Langmuir; LH; Langmuir–Hinshelwood; MOX; moxifloxacin; NCR; non-captured radicals; PDA; photo diode array; ROS; reactive oxygen species; VB; valence band; WWTPs; waste water treatment plantsHeterogeneous photocatalysis; Process parameters; Fluoroquinolone; Scavenger; Antibiotics

Deactivation characteristics of Ni/CeO₂-Al₂O₃ catalyst for cyclic regeneration in a portable steam reformer by Sungchul Lee; Gayatri Keskar; Changchang Liu; William R. Schwartz; Charles S. McEnally; Ju-Yong Kim; Lisa D. Pfefferle; Gary L. Haller (pp. 157-164).

Display Omitted► The active sites favored the formation of the carbidic carbon at high temperature. ► An interaction between the CeO₂ and Al₂O₃ was observed at high temperature. ► The nickel species were oxidized and reduced during the cyclic oxidation procedure. ► The deactivation under the cyclic oxidation condition is low in the long run test.The requirements of process parameters, e.g. air pump flow rate and operational pressure are restricted by confined space and limit the performance of portable steam propane reformer. This makes it difficult to operate a catalyst in the portable reformer under mild operation conditions. Hence, the catalyst can be rapidly deactivated. The deactivation behavior of Ni/CeO₂-Al₂O₃ catalyst was investigated for coke deposition and active metal sintering. Coke formation by the propane pyrolysis was predominantly responsible for deactivation at low reaction temperature. Coke formation can be thermodynamically reduced by elevating the temperature and hence the steam reformer was operated at high temperature to inhibit coke formation. Although the Ni/CeO₂-Al₂O₃ catalyst made small amounts of coke at high temperature, it was deactivated by the encapsulated carbon on active metal during long term operation. Because a compact air pump for catalyst regeneration was available during the shut-down procedure of our portable fuel cell system, the catalysts could be regenerated by coke oxidation. The cyclic oxidation was useful for long term operation. The properties of the used catalyst and the coke were investigated by XRD, NEXAFS, XANES-TPO, TGA and TEM. The Ni/CeO₂-Al₂O₃ catalyst in our portable reformer showed stable activity for steam propane reforming in cyclic oxidation operation for 500h.

Keywords: Reformer; Nickel; Catalyst; Deactivation; Regeneration

Microkinetic modelling for selective catalytic reduction (SCR) of NO_x by propane in a silver-based automotive catalytic converter by B. Sawatmongkhon; A. Tsolakis; K. Theinnoi; A.P.E. York; P.J. Millington; R.R. Rajaram (pp. 165-177).

Display Omitted► Detailed elementary reaction mechanism for C₃H₈-SCR with hydrogen. ► Rate parameters estimated by using microkinetic analysis. ► Two-dimensional Navier–Stokes equations coupled with a surface-reaction mechanism. ► Heat and mass-transfer correlation to link surface and bulk properties not required.A numerical simulation is designed in order to better understand the selective catalytic reduction of NO_x by propane (C₃H₈-SCR) in the presence of hydrogen. The simulation was designed for a single channel of a monolith typical for automotive catalytic converters, coated with a silver alumina catalyst (Ag/Al₂O₃). The complicated physical and chemical processes occurring during the reactions are solved by computational fluid dynamics (CFD) coupled with a surface-reaction mechanism. This mechanism is developed based on detailed microkinetic analysis. The elementary-step-like surface reaction mechanism (consisting of 94 reactions, 24 gas-phase species and 24 adsorbed surface species) is applied to investigate the effect on the conversion of NO_x to N₂ of chemical kinetic steps, such as intermediate species. Results from the modelling emphatically agree with the experimental data. The modelling can predict the NO_x conversion at various operating conditions. Furthermore, the modelling can also provide information that is difficult to measure, for example predicts the channel wall temperature and surface coverage of surface species.

Keywords: HC-SCR; Ag/Al; ₂; O; ₃; Emissions; Modelling

Improved dehydrogenation of ammonia borane over Co-P-B coating on Ni: A single catalyst for both hydrolysis and thermolysis by N. Patel; A. Kale; A. Miotello (pp. 178-184).

.Display Omitted► Co-P-B/Ni catalyst showed extraordinary catalytic activity for hydrolysis reaction of AB. ► AB loaded on Co-P-B/Ni catalyst releases first mole of H₂ at 80°C. ► Borazine and ammonia was minimizes by usage of Co-P-B/Ni catalyst.Co-P-B catalyst coatings have been synthesized on Ni-foam by using electroless deposition (ED) and their catalytic activity was investigated by catalytic dehydrogenation of ammonia borane (AB, NH₃BH₃) for H₂ generation. Co-P-B catalyst (both in form of powder and coating) showed superior catalytic activity in hydrolysis reaction of AB than that of Co-B powder, with complete evolution of H₂ (97%) at very high rate (2l/min/gcatalyst). This was mainly attributed to synergic effect caused by B and P over Co active sites to lower the activation energy of the process. For thermolysis reaction, it was observed that AB loaded on Co-P-B/Ni catalyst releases first mole of H₂ at considerably low temperature starting at 50°C and with desorption peak centered at 80°C. To our knowledge this value is the lowest reported for solid state catalyst. Moreover, the catalytic thermolysis did not present any induction time and minimizes the formation of undesirable byproduct like borazine and ammonia. The present result suggests that Co-P-B coated on Ni is a highly efficient and low cost catalyst and can be used for both hydrolysis as well as thermolysis reaction of NH₃BH₃ with the important advantage that it can be easily recovered and repeatedly reused.

Keywords: Hydrogen generation; Ammonia borane; Co-P-B coating; Electroless deposition; Thermolysis; Hydrolysis

Preparation, characterization and single-cell performance of a new class of Pd-carbon nitride electrocatalysts for oxygen reduction reaction in PEMFCs by Vito Di Noto; Enrico Negro; Stefano Polizzi; Pietro Riello; Plamen Atanassov (pp. 185-199).

Display Omitted► New plurimetal Pd-based carbon nitride ORR electrocatalysts are synthesized. ► For the first time the morphology, structure and electrochemical performance are investigated. ► A model is proposed to describe the chemical composition, structure and morphology. ► The electrochemical behaviour and fuel cell performance are carefully studied.This report describes the preparation of two Pd-based carbon nitride electrocatalysts for the oxygen reduction reaction (ORR) for application in polymer electrolyte membrane fuel cells (PEMFCs). The electrocatalysts consist of multi-metallic active sites supported on a graphite-like carbon nitride (CN) matrix with a N content exceeding 13wt%. The electrochemical performance is investigated by cyclic voltammetry with the thin-film rotating disk electrode method (CV-TF-RDE) and evaluated in a single membrane electrode assembly (MEA) PEMFC. The correlation of the structural information to functional properties allows to propose a reaction mechanism and to identify the most desirable features to achieve in a CN electrocatalyst in order to obtain desired electrochemical performance in catalysis of ORR. It is established also that the CN support improves the tolerance towards the catalyst corrosion under oxidizing conditions and thus improves the catalyst durability. The stoichiometry and the morphology of Pd-based CN electrocatalysts play a crucial role in the modulation of the tolerance towards common ORR poisons such as chlorine anions and methanol. Finally, the performance of the Pd-based CN electrocatalysts in a single MEA PEMFC proved promising.

Keywords: PEM fuel cells; Carbon nitride electrocatalysts; XPS; CV-TF-RDE method; MEA preparation

Core–shell nanostructure electrodes for improved electrocatalytic properties in methanol electrooxidation by Jong-Min Lee; Seong-Bae Kim; Young-Woo Lee; Do-Young Kim; Sang-Beom Han; Bumwook Roh; Inchul Hwang; Kyung-Won Park (pp. 200-207).

.Display Omitted► The TiN@C core–shell nanostructures have been successfully formed by heating process. ► The carbon shell structure shows graphitic-like properties. ► The thickness and crystallization of carbon can be controlled as a function of reaction time. ► The Pt deposited on TiN@C exhibits much improved electrocatalytic activities.TiN@C nanostructure supports consist of TiN as a core prepared at 900°C in NH₃ and carbon as a shell by heat treatment of the TiN at 900°C in CH₄ for 1, 3, and 6h (referred as TiN@C-1h, TiN@C-3h, and TiN@C-6h). The thickness of the carbon shell layers in the TiN@C supports increase with increasing reaction time at 900°C in CH₄. In particular, the TiN@C-1h supported Pt catalyst exhibits much improved electrocatalytic properties toward methanol electrooxidation as compared to Pt catalysts on Vulcan XC-72R.

Keywords: Core–shell; TiN@C; Nanostructure; Support; Methanol electrooxidation

Effects of structure, composition, and carbon support properties on the electrocatalytic activity of Pt-Ni-graphene nanocatalysts for the methanol oxidation by Yaojuan Hu; Ping Wu; Yajing Yin; Hui Zhang; Chenxin Cai (pp. 208-217).

Display Omitted► Graphene-supported Pt-Ni nanocatalyst was prepared by one-step reduction method. ► The catalyst with Pt/Ni ratio of 1:1 exhibited the highest activity toward MOR. ► This catalyst can greatly remove those poisoned intermediates in fuel cells reaction. ► The mechanism of the promoting effect of Ni on Pt was explained. ► The effect of support properties on activity of the catalyst was also elucidated.The structure, composition, morphology, and support material significantly affect the catalytic characteristics of Pt-based nanocatalysts. Fine control of the structural and compositional features is highly favorable for the creation of new Pt-based nanocatalysts with enhanced catalytic performance and improved Pt utilization. This work reports on a systematic and comparative study of the effects of structure, composition, and carbon support properties on the electrocatalytic activity and stability of Pt-Ni bimetallic catalysts for methanol oxidation, particularly the promoting effect of Ni on Pt. Graphene-supported Pt-Ni alloy nanocatalysts were prepared by a facile, one-step chemical reduction of graphene oxide and the precursors of Ni²⁺ and PtCl₆²⁻. The nanocatalysts were characterized by transmission electron microscopy (TEM), ultraviolet–visible spectrophotometry (UV–vis), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The electrocatalytic characteristics of the nanocatalysts were studied by voltammetry with methanol oxidation as a model reaction to evaluate the effects of the structure, surface composition, and electronic characteristics of the catalyst on the electrochemical activity. The catalyst with a Pt/Ni molar ratio of 1:1 exhibited the highest electrocatalytic activity for the methanol oxidation reaction with greatly lowered Pt utilization. The mechanism of the promoting effect of Ni on Pt is explained based on the modification of the electronic characteristics of the surface Pt atoms (Pt 4f) by Ni atoms due to the shift in the electron transfer from Ni to Pt and the synergistic roles of Pt and nickel hydroxides on the surfaces of the catalysts. The effects of the different carbon supports (i.e., graphene, single-walled carbon nanotubes, and Vulcan XC-72 carbon) on the electrocatalytic characteristics of the nanocatalysts are investigated by Raman and XPS experiments. The results demonstrate that the graphene-supported Pt-Ni catalyst has the highest electrocatalytic activity of the three carbon materials due to abundant oxygen-containing groups on the graphene surface, which can remove the poisoned intermediates and improve the electrocatalytic activity of the catalysts.

Keywords: Pt-Ni nanocatalysts; Graphene; Electrocatalysis; Methanol oxidation

Catalytic performance of core–shell and alloy Pd–Au nanoparticles for total oxidation of VOC: The effect of metal deposition by M. Hosseini; T. Barakat; R. Cousin; A. Aboukaïs; B.-L. Su; G. De Weireld; S. Siffert (pp. 218-224).

Display Omitted► Pd(shell)–Au(core)/TiO₂, Au(shell)–Pd(core)/TiO₂ and Pd–Au(alloy)/TiO₂ catalysts for VOC oxidation. ► Higher activity of Pd(shell)–Au(core)/TiO₂. ► Competition observed by operando DRIFT for adsorption between toluene and propene molecules. ► Mechanism of oxidation proceeds through preferential adsorption of oxygen than VOC.The catalytic properties of palladium and gold nanoparticles deposited on mesoporous TiO₂ are investigated in toluene and propene oxidation. The catalysts, containing Pd and Au deposited on mesoporous TiO₂ have been prepared by different order of metal deposition (Pd(shell)–Au(core)/TiO₂, Pd–Au(alloy)/TiO₂ and Au(shell)–Pd(core)/TiO₂. For both toluene and propene oxidation reactions, the catalytic activity was found significantly higher when palladium is deposited on already-deposited gold (Pd(shell)–Au(core)/TiO₂). This enhanced activity could be explained by the core–shell morphology (Pd–shell and Au-core) observed by UV–vis spectra, TPR profiles and XPS spectra. It was suggested that the oxidation reaction follows a Langmuir–Hinshelwood mechanism where the molecules of oxygen and VOC are in competition for adsorption on the surface of catalyst. Operando DRIFT spectroscopy was carried out to test the catalytic activity in a mixture of volatile organic compounds (toluene and propene). It was demonstrated that there is a competition between the molecules of VOC for adsorption but also the toluene has an inhibition effect for oxidation of propene.

Keywords: VOC oxidation; Palladium; Gold; Mesoporous TiO; ₂; Core–shell; Alloy; UV–vis diffraction; Operando DRIFT; TPR

Glycerol steam reforming for hydrogen production: Design of Ni supported catalysts by Valentina Nichele; Michela Signoretto; Federica Menegazzo; Alessandro Gallo; Vladimiro Dal Santo; Giuseppe Cruciani; Giuseppina Cerrato (pp. 225-232).

Display Omitted► Ni catalysts have been tested in glycerol steam reforming for H₂ production. ► A strong effect of the support on the catalytic activity has been detected. ► TiO₂ cannot stabilize metallic Ni species on the surface. ► SBA-15 collapses in the reaction conditions because of its low hydrothermal stability. ► ZrO₂ exhibits the best performance and stabilizes Ni nanoparticles to a high degree.In this work the activity of Ni catalysts in hydrogen production by glycerol steam reforming was studied. Moreover the effect of the support (TiO₂, SBA-15 and ZrO₂) on the catalytic performance of Ni was evaluated. A strong effect of the support on the activity of the samples was detected. The Ni/TiO₂ sample showed negligible activity mainly due to the low strength of anatase to keep nickel in the reduced state. In fact, both incorporation of Ni ions into the nanoanatase lattice and oxidation of the active phase to NiO under operating conditions were observed. A deactivation process was also found with the Ni/SBA-15 sample while the best results were achieved with the Ni/ZrO₂ catalyst, showing no deactivation. After 20h, the glycerol conversion was ∼72% and the H₂ yield was ∼65%. The Ni/ZrO₂ sample was even more active when tested at lower temperatures, although its performance was less stable. On the basis of the experimental results, it was evidenced that the nature of the support affects above all the stability of the active phase. In particular, strong interactions between the metal active phase and the support ensures stability, activity and selectivity of the catalyst in glycerol steam reforming reactions.

Keywords: Hydrogen; Glycerol; Steam reforming; Biodiesel; Nickel

Deactivation of Pd/Ce_0.5Zr_0.5O₂ model three-way catalyst by P, Ca and Zn deposition by S.Y. Christou; S. García-Rodríguez; J.L.G. Fierro; A.M. Efstathiou (pp. 233-245).

Effects of P, P-Ca and P-Zn deposition on the surface of 1wt% Pd/Ce0.5Zr0.5O2 catalyst followed by calcination at 850°C on the OSC (a) and CO conversion (1%CO/0.2%C₃H₆/1%O₂/He) (b).The negative effects of P, P-Ca and P-Zn deposition on the surface of a model 1wt% Pd/Ce_0.5Zr_0.5O₂ “three-way” catalyst (TWC) on its structural, morphological, textural, oxygen storage and release, and catalytic performance have been investigated for the first time. The aim of this research work is to provide fundamental understanding on the multiple functions of a TWC when P, Ca and Zn contaminants are accumulated on its surface. Towards this aim, a model Pd/Ce_0.5Zr_0.5O₂ TWC and P, P-Ca and P-Zn contaminated ones were prepared and ischaracterised by means of BET, XRD, HR-TEM, XPS and H₂/O₂ pulse injection techniques. The catalytic performance of the non-contaminated and contaminated Pd/Ce_0.5Zr_0.5O₂ solids was evaluated for CO and C₃H₆ oxidation and NO reduction by H₂ probe reactions under oxygen lean conditions. Incorporation of P, Ca and Zn contaminants was found to cause a significant decline (16–40%) in the concentration (μmol O/g) of labile active (OSC) and total (OSCC) oxygen species of Pd/Ce_0.5Zr_0.5O₂ catalyst aged in air at 850°C. After P incorporation followed by calcination at 850°C, CePO₄ was detected, while in the presence of Ca or Zn the formation of Ca₃(PO₄)₂ and ZnO, respectively, was verified. At low reaction temperatures, co-addition of Zn and P was found to further deteriorate the OSC (μmol O/g), while at high temperatures no appreciable differences were observed. This is ascribed to the formation of CePO₄ which decreases significantly the degree of reduction of Ce(IV) oxide. CePO₄ physically covers catalyst particles (e.g., pore mouth and internal surface) leading to the substantial loss of BET area, pores volume, and Pd surface sites. More importantly, it is shown for the first time that the presence of Pd was found to diminish to a great extent the deteriorating effect of P, Ca and Zn when deposited on Ce_0.5Zr_0.5O₂ on its oxygen storage and release properties. High concentrations (mg/g) of P, P-Ca and P-Zn contaminants on the catalyst surface was found to cause a considerable decrease in catalyst's activity for CO and C₃H₆ oxidation, and NO reduction by H₂ under oxygen lean conditions. The deterioration of catalytic performance is largely due to the presence of P, and to a lesser extent to the presence of Ca or Zn.

Keywords: “Three-way” catalyst; Catalyst deactivation; P, Ca and Zn chemical poisoning; Oxygen storage capacity; OSC; CO oxidation; C; ₃; H; ₆; oxidation; NO reduction

Simulated solar-light assisted photocatalytic ozonation of metoprolol over titania-coated magnetic activated carbon by Ana Rey; Diego H. Quiñones; Pedro M. Álvarez; Fernando J. Beltrán; Pawel K. Plucinski (pp. 246-253).

Display Omitted► The TiO₂-coated magnetic activated carbon (TiFeC) showed moderate magnetic properties. ► TiFeC led to total removal of MTP and high mineralization degree by solar photocatalytic ozonation. ► TiFeC was easily separable by a magnet and showed good stability and reusability. ► Solar photolytic ozonation (without catalyst) effectiveness was noticeable.A magnetically separable photocatalyst consisting of magnetic porous activated carbon with attached anatase TiO₂ particles has been prepared and tested for the degradation of metoprolol (MTP) in aqueous solution. The synthesized photocatalyst (TiFeC) was characterized by nitrogen adsorption, XRD, FTIR, SEM, EDX and SQUID magnetometer. The obtained catalyst with a TiO₂ composition of 61wt.% (mostly anatase) had moderate surface area (BET surface of 331m²g⁻¹) and volume of micropores and exhibited magnetic properties with saturation magnetization of 1.6emug⁻¹ and neither remanent magnetization nor coercivity. The photocatalytic activity of TiFeC samples was tested by degrading MTP by simulated solar photocatalytic ozonation. The results were compared to those obtained with a commercial titania (Degussa P25) and by photolytic ozonation (i.e., absence of catalyst). Complete MTP removal and more than 60% TOC conversion were achieved after 3h of photocatalytic ozonation of an aqueous solution containing as much as 50mgL⁻¹ MTP initial concentration. The reusability and stability of the catalyst were tested through a series of five photocatalytic ozonation experiments. Minor amounts of iron and titanium were leached out from the catalyst and the catalytic activity decreased to a very low extent with the reuse of the catalyst.

Keywords: Solar photocatalysis; Ozone; Magnetic catalyst; Pharmaceuticals; Water treatment

Heterogeneous Fenton using ceria based catalysts: effects of the calcination temperature in the process efficiency by André F. Rossi; Nuno Amaral-Silva; Rui C. Martins; Rosa M. Quinta-Ferreira (pp. 254-263).

Total organic carbon removal (%) curves along the experiments.Display Omitted► Ceria based iron catalysts have proved their good performance for organic compounds removal. ► Fe–Ce catalyst calcinated at 300°C (C₃₀₀) was the most active for heterogeneous Fenton's. ► Oxidation pathway mainly followed surface reaction routes. ► C₃₀₀'s samples eliminated toxicity and enhanced biodegradability levels.The need of more efficient solid catalysts for the heterogeneous slurry Fenton process led many investigators to research new compounds activities. Ceria based iron catalysts have proved their good performance enhancing the removal of organic compounds, reducing toxicity and improving biodegradability in the depuration of phenolic wastewaters. This work evaluates the calcination temperature (300°C, 600°C and 1000°C) during the preparation of the catalysts—co-precipitation of the precursors salts, while the same previously optimized conditions were adopted (pH 3.0, 1.0gL⁻¹ of Fe–Ce–O 70/30 as the catalyst, [H₂O₂]=244mM and 120min of room temperature reaction) to treat a simulated wastewater comprising 0.1gL⁻¹ of each of the six common phenolic acids found in Olive Mills wastewaters. The three obtained solids were characterized regarding superficial area, average pore diameter, FT-IR and XRD. Catalysts calcinated at 300°C, 600°C and 1000°C presented superficial areas of 188, 86 and 2m²/g, respectively, and their average pore diameter are 66, 87 and 151Å, correspondingly. As showed in the XRD, the increase of the calcination temperature promotes the crystallinity of the obtained solid—higher amount of prominent peaks, meaning that the catalysts have different states of valence for iron (Fe²⁺ or Fe³⁺) and ceria (Ce²⁺ to Ce⁴⁺), what would explain their singular behaviours during the reaction. As expected, the solids with higher superficial areas had better performances in every aspect: more COD, TOC and phenolic acids removal, pointing the lowest calcination temperature as leading to a more efficient solid to enhance hydrogen peroxidation, involving, however, more metal leaching. The higher the calcination temperature is, the more oxidized the solid will become because the calcination occurs without atmospheric control and so the oxygen contained in the air will interfere on the valence of iron ions at the solid's surface. This means that a solid calcinated at a higher temperature will have increased Fe³⁺ content and, as one can find in the literature, Fe²⁺ is more effective than Fe³⁺ at hydrogen peroxidation, explaining the better efficiency of the catalyst calcinated at the lowest temperature. Toxicological and biodegradability studies were still performed and showed enhancement in all cases.

Keywords: Heterogeneous Fenton's process; Catalyst characterization; Environment protection; Phenolic acids; Toxicity

Effect of particle size on the activity and durability of the Pt/C electrocatalyst for proton exchange membrane fuel cells by Zhuang Xu; Huamin Zhang; Hexiang Zhong; Qiuhong Lu; Yunfeng Wang; Dangsheng Su (pp. 264-270).

Display Omitted► In situ electrochemical synthesis for Pt with various particle sizes. ► Surface specific activity and electrochemical stability improved with Pt particle size increase. ► Reduced defects on the Pt surface weaken the adsorption of oxygenated species releasing more available active sites. ► Fuel cell durability sharply increased when Pt exceeding 3nm. ► Designing Pt with more face atom occupation would obtain more active and durable PEMFC catalyst.Carbon supported Pt (Pt/C) with various average particle sizes ranging from sub 3nm to 6.5nm were in situ prepared and characterized at the cathode of proton exchange membrane fuel cells (PEMFCs). A clear Pt particle size effect on both the catalytic activity for oxygen reduction reaction (ORR) and the durability of the electrocatalyst was revealed. With the Pt particle size increase, both the surface specific activity and the electrochemical stability of Pt/C improved; however, the mass specific activity of Pt/C is balanced by the electrochemical surface area loss. The reduced occupation of corner and edge atoms on the Pt surface during the Pt particle size increase is believed to weaken the adsorption of the oxygenated species on Pt, and thereafter releases more available active sites for ORR and also renders the Pt surface a stronger resistance against potential cycling. It is therefore proposed that by designing the Pt microstructure with more face atoms on the surface, cathode electrocatalyst with both improved activity and enhanced durability would be developed for PEMFCs.

Keywords: Proton exchange membrane fuel cells; Pt/C electrocatalyst; Particle size; Activity; Durability

Synthesis, characterization and photocatalytic performance of novel visible-light-induced Ag/BiOI by Hong Liu; Weiran Cao; Yun Su; Yong Wang; Xiaohong Wang (pp. 271-279).

Display Omitted► Ag/BiOI catalyst with flower-like morphology can be obtained. ► Such material exhibits strong spectral response in the visible region. ► The photocatalytic activity of BiOI was greatly enhanced by the deposition of Ag. ► Ag nanoparticles could act as electron traps to promote the electron–hole separation.For the first time, a series of Ag/BiOI photocatalysts with different Ag contents have been synthesized by a hydrothermal combinated with photodeposition method. The as-prepared products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high-resolution transmission electron micrographs (HRTEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra (DRS), and photoluminescence (PL) emission spectroscopy. The photocatalytic activities of these Ag/BiOI composites under visible-light irradiation ( λ>420nm) were evaluated by the degradation of acid orange II, methyl orange (MO) and rhodamine B (RB). The results revealed that the Ag/BiOI composites exhibited much higher photocatalytic activities than pure BiOI. The Ag amount in the Ag/BiOI composites played an important role in the corresponding photocatalytic properties and the optimized ratio was obtained at 0.6%. The significant enhancement in the Ag/BiOI photoactivity could be ascribed to both the effect of Ag deposits by acting as electron traps and the surface plasma resonance effect of Ag.

Keywords: Ag/BiOI; Visible-light photocatalysis; Electron–hole separation; Dyes

Combination of cobalt ferrite and graphene: High-performance and recyclable visible-light photocatalysis by Yongsheng Fu; Haiqun Chen; Xiaoqiang Sun; Xin Wang (pp. 280-287).

Display Omitted► A magnetically separable CoFe₂O₄-graphene photocatalyst was successfully synthesized. ► The combination of CoFe₂O₄ nanoparticles with graphene results in a dramatic conversion of the inert CoFe₂O₄ into a highly active catalyst for the degradation of organic dyes. ► The significant enhancement in photoactivity under visible-light irradiation can be ascribed to reduction of graphene oxide.A straightforward strategy was designed for the fabrication of magnetically separable CoFe₂O₄-graphene photocatalysts with differing graphene content. It is very interesting that the combination of CoFe₂O₄ nanoparticles with graphene results in a dramatic conversion of the inert CoFe₂O₄ into a highly active catalyst for the degradation of methylene blue (MB), Rhodamine B (RhB), methyl orange (MO), active black BL-G and active red RGB under visible-light irradiation. The significant enhancement in photoactivity under visible-light irradiation can be ascribed to reduction of graphene oxide, because the photogenerated electrons of CoFe₂O₄ can transfer easily from the conduction band to the reduced graphene oxide, effectively preventing a direct recombination of electrons and holes. Hydroxyl radicals play the role of main oxidant in the CoFe₂O₄-graphene system and the radicals’ oxidation reaction is obviously dominant. CoFe₂O₄ nanoparticles themselves have a strong magnetic property, which can be used for magnetic separation in a suspension system, and therefore the introduction of additional magnetic supports is no longer necessary.

Keywords: Cobalt ferrite; Graphene; Photocatalyst; Magnetic separation; Visible-light irradiation

Thermodecomposition synthesis of WO₃/H₂WO₄ heterostructures with enhanced visible light photocatalytic properties by Jing Cao; Bangde Luo; Haili Lin; Benyan Xu; Shifu Chen (pp. 288-296).

Novel WO₃/H₂WO₄ heterostructures were synthesized through a simple thermodecomposition method. The WO₃/H₂WO₄ heterostructures exhibited enhanced photocatalytic activity compared to single WO₃ and H₂WO₄ toward degradation of rhodamine B (RhB) under visible light irradiation ( λ>420nm). The resultingO₂⁻ and active h⁺ played the major roles for the degradation of RhB whileOH was verified to be insignificant. The formation of heterojunction between WO₃ and H₂WO₄ is responsible for the enhanced photoactivities of WO₃/H₂WO₄, which can facilitate separation of photoinduced carriers.Display Omitted► WO₃/H₂WO₄ heterostructure is a novel composite photocatalyst. ► WO₃/H₂WO₄ was synthesized via partial thermodecomposition method. ► WO₃/H₂WO₄ displays excellent visible light photocatalytic activity ( λ>420nm). ► The resultingO₂⁻ and active h⁺ played the major roles for RhB degradation. ► Partial thermodecomposition offers a new way to design composite photocatalysts.Novel WO₃/H₂WO₄ heterostructures with different contents of WO₃ were synthesized through a simple thermodecomposition method. Thermogravimetry and differential thermal analysis (TG–DTA), X-ray powder diffraction (XRD), Fourier transform infrared spectrometry (FT-IR), UV–vis diffuse reflectance spectroscopy (DRS) and N₂ adsorption and desorption isotherms were employed to study the structures, morphologies, optical properties and specific surface area of the as-prepared samples. Degradation of rhodamine B (RhB) was carried out to evaluate the photocatalytic activity of samples under visible light irradiation ( λ>420nm). WO₃/H₂WO₄ heterostructure with 51.04wt% WO₃ presented the highest photocatalytic activity with apparent k_app of 0.0330min⁻¹. The increased photocatalytic activity of WO₃/H₂WO₄ could be attributed to the formation of the heterojunction between WO₃ and H₂WO₄, which suppresses the recombination of photoinduced electron–hole pairs. Moreover, the tests of radical scavengers confirmed thatO₂⁻ and h⁺ were the main reactive species for the degradation of RhB.

Keywords: WO; ₃; /H; ₂; WO; ₄; Thermodecomposition; Photocatalytic activity; Mechanism

Photocatalytic hydrogen formation from ammonia and methyl amine in an aqueous suspension of metal-loaded titanium(IV) oxide particles by Hiroshi Kominami; Haruhiko Nishimune; Yuichi Ohta; Yuma Arakawa; Takenori Inaba (pp. 297-302).

Display Omitted► Photoirradiation to NH₃ in aqueous suspensions of metal-loaded TiO₂ was examined. ► NH₃ was photocatalytically decomposed to H₂ and N₂ with a stoichiometric ratio. ► Platinum showed the greatest effect as a co-catalyst. ► Reaction of methyl amine was expressed as CH₃NH₂+3H₂O→3H₂+NH₄⁺+HCO₃⁻.Photocatalytic hydrogen (H₂) formation from ammonia and methyl amine in aqueous suspensions of metal-loaded titanium(IV) oxide (TiO₂) particles was examined under various conditions. Ammonia was decomposed to H₂ and nitrogen (N₂) with a stoichiometric ratio (3:1, 2NH₃→3H₂+N₂) under a deaerated condition, and side reactions such as deep oxidation of ammonia to nitrite and nitrate did not occur. The rate of H₂ formation drastically changed depending on the co-catalyst loaded on TiO₂ particles, kinds of TiO₂ samples and pH of the suspension. The effect of the co-catalyst became greater with decrease in hydrogen over-voltage, the value of which was obtained when the co-catalyst metal was used as an electrode. Among the co-catalysts used in this study, platinum showed the greatest effect as a co-catalyst. The largest rate of H₂ evolution was obtained when the photocatalytic reaction was carried out at pH 10.7, and addition of an acid or base to the suspension decreased the reaction rate. Photocatalytic reaction of methyl amine in aqueous suspension of platinized TiO₂ particles under a deaerated condition yielded H₂ but did not form N₂. The methyl group of methyl amine was mineralized and the amino group remained as ammonium ion without being decomposed to H₂ and N₂, resulting in storage of carbon as hydrogencarbonate (HCO₃⁻) in the suspension. Photocatalytic reaction of methyl amine under the present conditions was totally expressed as CH₃NH₂+3H₂O→3H₂+NH₄⁺+HCO₃⁻.

Keywords: Photocatalyst; Titanium(IV) oxide; Hydrogen formation; Ammonia; Methyl amine

Enhanced photocatalytic degradation of methylene blue under visible irradiation on graphene@TiO₂ dyade structure by Donglin Zhao; Guodong Sheng; Changlun Chen; Xiangke Wang (pp. 303-308).

Display Omitted►A visible-light photocatalysis of graphene@TiO₂ was synthesized. ►The graphene@TiO₂ absorbed a high amount of photo energy in the visible-light region. ►There were moreOH radicals produced by the graphene@TiO₂ (1:3) than by pure TiO₂ under UV and visible-light irradiation. ► Graphene can enhance the photocatalytic activity of TiO₂.Electron–hole recombination limits the efficiency of TiO₂. We have investigated the efficacy with which the graphene@TiO₂ “dyade”-like structure reduced charge recombination and enhanced reactivity. A visible-light photocatalysis of graphene@TiO₂ “dyade”-like structure was synthesized, and photocatalytic degradation of organic compounds over the UV and visible-light spectrum regions was investigated. The graphene@TiO₂ had anatase phase and was able to absorb a high amount of photo energy in the visible-light region, driving effectively photochemical degradation reactions. There were moreOH radicals produced by the graphene@TiO₂ (1:3) than by pure TiO₂ under UV and visible-light irradiation. Graphene can enhance the photocatalytic activity of TiO₂ in two aspects, namely, e⁻ transportation and adsorption. This work provides new insight into the fabrication of graphene@TiO₂ as a high performance visible-light photocatalyst and facilitates its application in photocatalytic degradation of organic compounds.

Keywords: Graphene; Photocatalysis; TiO; ₂; Degradation

Characterization and reactivity of Al₂O₃ supported Pd-Ni bimetallic catalysts for hydrodechlorination of chlorobenzene by N. Seshu Babu; N. Lingaiah; P.S. Sai Prasad (pp. 309-316).

Display Omitted► Pd-Ni bimetallic catalysts with low Pd are highly active for hydrodechlorination. ► Variation of surface, structural and geometrical features related to Pd-Ni content. ► Hydrodechlorination activity depends on method of catalyst preparation. ► The catalysts are stable for the hydrodechlorination of chlorinated hydrocarbons.A series of Al₂O₃ supported bimetallic Pd-Ni catalysts were prepared by deposition–precipitation method. The physico-chemical properties of the catalysts were evaluated by different characterization techniques such as temperature programmed reduction (TPR), temperature programmed desorption of H₂ (TPD), X-ray photoelectron spectroscopy (XPS), Braunner–Emmet–Teller (BET) surface area and pulse CO chemisorption. The activities of bimetallic Pd-Ni/Al₂O₃ catalysts were evaluated for continuous fixed bed gas phase hydrodechlorination of chlorobenzene operating at 140°C under atmospheric pressure. The activity profiles demonstrate that an exceptional activity and stability of Pd-Ni/Al₂O₃ catalysts is accomplished by judicial variation of Ni composition with respect to Pd, which had arrived at Pd and Ni in 0.5:0.5 (wt%) ratio, while high Ni loaded Pd-Ni catalysts exhibit poorer stability. The high activity and stability of optimal catalyst is invoked due to formation of very active Pd-Ni interfaces embedded with Pd δ⁺ species, whereas lower stability resulted in high Ni loaded catalysts is due to aggregation of Ni component on topical Pd surface. The activity of mono and bimetallic catalysts are well correlate with the characterization results.

Keywords: Bimetallic Pd-Ni catalysts; Alumina; Deposition–precipitation; Hydrodechlorination; Chlorobenzene

Boosting the electrocatalytic activities of SnO₂ electrodes for remediation of aqueous pollutants by doping with various metals by So Young Yang; Yeon Sik Choo; Soonhyun Kim; Sang Kyoo Lim; Jaesang Lee; Hyunwoong Park (pp. 317-325).

Ni-doped Sb–SnO₂ anodes are very effective in degradation of aqueous pollutants through a direct electron transfer and/or organic peroxy radical-mediation.Display Omitted► The electrocatalytic activity of SnO₂ was highly affected by doping with metals. ► Sb with a 5–10at.% was most effective in making SnO₂ an electrocatalyst. ► Ni doping markedly accelerated the degradation of phenol and Eosin Y at Sb–SnO₂. ► Direct electron transfer and involvement of peroxy radicals played a critical role.The purpose of this study is to search for effective dopants and their optimal combinations to improve the electrocatalytic activity of the SnO₂ electrode for the remediation of aqueous pollutants. For this purpose, Sb was selected as the primary dopant for SnO₂ and six elements (Fe(III), Ni(II), Co(II), Ru(III), Ce(III), and Pd(II)) were also introduced into the optimized Sb–SnO₂ electrodes. The electrodes were checked for their electrochemical properties at different doping levels and tested for their electrocatalytic activities for the degradation of phenol and Eosin Y. In addition, RNO (N,N-dimethyl-p-nitrosoaniline) was used as a probe molecule for OH radicals to examine the reaction mechanism occurring at the electrodes. Sb with a 5–10at.% was most effective in making SnO₂ an electrocatalyst and Ni (∼1%) enhanced the degradation rate and TOC removal rate of phenol at the Sb–SnO₂ anode by a factor of 14 and 8, respectively. Fe also increased the activity moderately. Enhanced Ni–Sb–SnO₂ activity was also found for Eosin Y. The other co-dopants exhibited various degrees of positive or negative effects depending on the substrate. The lack of a correlation in the kinetics between substrate degradation and the RNO changes indicated that the primary electrocatalytic reactions may proceed via direct electron transfer and/or organic peroxy radical-mediation, not OH radical-mediation. Detailed analyses of the electrode surfaces (SEM, TEM, XRD, and XPS) and quantification of intermediates were carried out to obtain insight into the heterogeneous electrocatalytic reaction.

Keywords: Electrocatalytic; Water treatment; Antimony; Sb–SnO; ₂; Doping

Enhanced visible-light photocatalytic activity of Bi₂WO₆ nanoparticles by Ag₂O cocatalyst by Huogen Yu; Rui Liu; Xuefei Wang; Ping Wang; Jiaguo Yu (pp. 326-333).

Display Omitted► The Ag₂O-loaded Bi₂WO₆ nanoparticles exhibited enhanced photocatalytic activity. ► Ag–Ag₂O was demonstrated to be a new and effective oxygen-reduction cocatalyst. ► The Ag–Ag₂O cocatalyst possibly reduces oxygen via a multi-electron transfer mechanism.Cocatalyst modification is an efficient strategy to improve the photocatalytic efficiency of photocatalysts by promoting the effective separation of photogenerated electrons and holes. However, most of the cocatalysts are restricted to noble metals (e.g., Ag, Au, Pt) and seldom investigation has been focused on their oxides. In this study, Ag₂O cocatalyst was coated on the surface of Bi₂WO₆ nanoparticles by an impregnation method followed by a low-temperature treatment (100–350°C) and their photocatalytic performance was evaluated by the photocatalytic decolorization of methyl orange solution under visible-light irradiation. It was found that after the surface coating of Ag₂O, the obtained Ag₂O/Bi₂WO₆ composites exhibited an obvious higher photocatalytic activity than the unmodified Bi₂WO₆ nanoparticles and N-doped TiO₂. Owing to the photosensitive property of pure Ag₂O phase, the Ag–Ag₂O composite easily formed during the decomposition process of organic substances under visible-light irradiation. On the bases of experimental result and band structure analysis, an Ag–Ag₂O cocatalyst-enhanced photocatalytic mechanism is proposed; namely, the Ag–Ag₂O cocatalyst possibly reduces oxygen via a multi-electron transfer mechanism. The present results suggest that Ag–Ag₂O can act as a new and effective cocatalyst for the enhanced photocatalytic performance of photocatalysts, which provides a new approach for the design and development of high-performance visible-light photocatalysts.

Keywords: Cocatalyst; Ag–Ag; ₂; O; Photocatalysis; Bi; ₂; WO; ₆; Visible light

Solvothermal synthesis of flower-like BiOBr microspheres with highly visible-light photocatalytic performances by Yuning Huo; Jia Zhang; Miao Miao; Yi Jin (pp. 334-341).

Display Omitted► Hierarchical flower-like BiOBr microspheres assembled with nanosheets are prepared by solvothermal process in two-component solvent. ► The growth of BiOBr crystal is controlled by the ratio of ethylene glycol and isopropanol, the amount of CTAB surfactant and the solvothermal time. ► High visible photoactivity is due to strong light absorbance via light multi-reflections and efficient separation of photo-induced charges. ► TheO₂⁻ radical is the main active species during the photocatalytic reaction. ► The durability of BiOBr photocatalyst is owing to the stable crystal phase and microsphere morphology.Hierarchical flower-like BiOBr microspheres assembled with nanosheets were synthesized via solvothermal method with both two-component solvent (ethylene glycol and isopropanol) and CTAB surfactant. The growth of BiOBr crystal was significantly influenced by the concentration of ethylene glycol and isopropanol in two-component solvent, the amount of CTAB surfactant and the solvothermal time. According to the photodegradation of rhodamine B (RhB) under visible-light irradiations, the high photocatalytic activity of hierarchical flower-like BiOBr microspheres could be ascribed to the enhanced visible-light absorbance via the light multi-reflections, the efficient separation of photo-generated electrons and holes, the high crystallization and the large surface area. The main active species during the photocatalytic reaction was determined asO₂⁻ radical by additionally dissolving the trapping agent in the solution. Meanwhile, BiOBr microspheres also exhibited the excellent durability owing to the stable crystal phase and microsphere morphology.

Keywords: Hierarchical flower-like BiOBr microsphere; Solvothermal preparation; Two-component solvent; Visible-light photocatalyst; Degradation of rhodamine B

Isothermal desulfation of pre-sulfated Pt-BaO/γ-Al₂O₃ lean NOx trap catalysts with H₂: The effect of H₂ concentration and the roles of CO₂ and H₂O by Do Heui Kim; Ja Hun Kwak; János Szanyi; Charles H.F. Peden (pp. 342-348).

Display Omitted► Sulfates were found to be reduced with H₂ to produce SO₂, followed by the formation of H₂S. ► The sulfur removal efficiency is initially proportional to the H₂ concentration, then leveled off. ► At constant H₂ concentration the overall desulfation efficiency decreases in the order of H₂/CO₂/H₂O>H₂/CO₂>H₂/H₂O>H_2. ► H₂O enhances the production of H₂S in later stages of reduction. ► CO₂ is involved in both the formation of COS and the production of H₂O.The desulfation mechanisms of pre-sulfated Pt-BaO/γ-Al₂O₃ lean NOx trap catalysts were investigated under isothermal conditions (600°C) using H₂ as the reductant. Sulfates were found to be reduced first with H₂ to produce SO₂, followed by a reaction between SO₂ and H₂ to produce H₂S. Gas analysis during the rich pulse reveals that the sulfur removal efficiency is initially proportional to the H₂ concentration. At constant H₂ concentration the overall desulfation efficiency decreases in the order of H₂/CO₂/H₂O>H₂/CO₂>H₂/H₂O>H₂, as confirmed by XPS analysis of residual sulfur in the desulfated samples. H₂O limits the evolution of SO₂ at an early stage of the rich pulse and enhances the production of H₂S in later stages of reduction. CO₂ is involved in both the formation of COS and the production of H₂O (via the reverse water–gas shift reaction), therefore, resulting in an increased overall efficiency.

Keywords: Pt-BaO/γ-Al; ₂; O; ₃; SO; ₂; Lean NOx trap; Desulfation; H; ₂; S; COS

Oxy-chlorination as an effective treatment of aged Pd/CeO₂-Al₂O₃ catalysts for Pd redispersion by Panagiota S. Lambrou; Kyriaki Polychronopoulou; Klito C. Petallidou; Angelos M. Efstathiou (pp. 349-359).

Effect of oxy-chlorine gas treatment followed by H₂ reduction applied over a 5wt% Pd/20wt% CeO₂-Al₂O₃ catalyst on the CO oxidation reaction.Display Omitted► Oxy-chlorine gas treatment can reduce Pd particle size from 17 to 8nm in Pd/CeO₂-Al₂O₃. ► Oxy-chlorine gas treatment over 5wt% Pd/CeO₂-Al₂O₃ increases significantly OSC. ► Oxy-chlorine gas treatment over 5wt% Pd/CeO₂-Al₂O₃ increases significantly CO oxidation rates and NO chemisorption. ► Oxy-chlorine gas treatment over 5wt% Pd/CeO₂-Al₂O₃ improves Pd–ceria support interactions in favour of OSC. ► Oxy-chlorine gas treatment for Pd redispersion on Pd/CeO₂-Al₂O₃ is superior to O₂/H₂ treatments.The present work reports on the effects of oxy-chlorine gas treatment (use of Cl₂/O₂/He gas mixture) applied on a 5wt% Pd/20wt% CeO₂-Al₂O₃ catalyst towards Pd redispersion. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HR-TEM), temperature programmed reduction in H₂ (H₂-TPR) and in situ diffuse reflectance infrared Fourier transformed spectroscopy (DRIFTS) NO chemisorption techniques were employed before and after use of the oxy-chlorine gas treatment to critically evaluate its efficiency. The composition ( xvol% Cl₂/18vol% O₂/He), temperature, and time on stream were investigated. The first two parameters were found to largely dictate optimum Pd redispersion, namely the use of a 2vol% Cl₂/18vol% O₂/He gas mixture at 500°C for 1h, where a significant reduction of an initial Pd mean particle size of 17.3–7.5nm was obtained. XPS studies revealed that after oxy-chlorine gas treatment followed by H₂ reduction at 500°C, complete elimination of Cl from the Pd surface was achieved. The oxygen storage capacity (OSC) of the catalyst measured following different oxy-chlorine gas treatments was found to significantly increase. Catalytic activity towards CO oxidation along with in situ DRIFTS NO chemisorption studies proved the large effect of the oxy-chlorine gas treatment on increasing the CO oxidation rate and the extent of NO chemisorption. Alternative treatment in oxygen gas atmosphere at high temperatures (500–850°C) followed by H₂ reduction (300–500°C) applied over the same catalyst failed to cause significant redispersion of Pd as observed with the oxy-chlorine gas treatment.

Keywords: Pd redispersion; X-ray photoelectron spectroscopy; Oxygen storage capacity; Oxy-chlorination treatment; CO oxidation; NO chemisorption

Tailoring MgO-based supported Rh catalysts for purification of gas streams from phenol by K. Polychronopoulou; K. Giannakopoulos; A.M. Efstathiou (pp. 360-375).

Effect of support chemical composition on the H₂ yield (%) obtained over the 0.1wt% Rh/40Mg-25Ce-25Zr-20X-O (X=La, Ba, Zn, Ca, Sr) catalysts in the 575–735°C range after phenol steam reforming (0.5% C₆H₅OH/40% H₂O/He; t=30min; GHSV=80,000h⁻¹). Results are also shown for the 0.1wt% Rh/50Mg-25Ce-25Zr-O and commercial 44wt% NiO/γ-Al₂O₃ catalysts.Display Omitted► La³⁺ addition in Rh/Mg-Ce-Zr-O largely enhances its phenol steam reforming activity. ► The beneficial role of La³⁺ is largely due to the enhanced concentration of active support labile O. ► Acid/basic surface properties of Mg-Ce-Zr-X-O (X=La³⁺, Sr²⁺, Ca²⁺, Ba²⁺, Zn²⁺) regulates phenol steam reforming activity. ► Steam is more effective than oxygen in removing “carbon” deposits formed after phenol steam reforming.The present work is focused on the sol–gel synthesis, characterization and catalytic performance evaluation of novel Mg-Ce-Zr-O-based mixed oxides supported Rh catalysts for the purification of H₂-rich gas streams from phenol through steam reforming in the 575–730°C range. Phenol is used as a model compound of tars, the former being one of the main constituents of tars formed during steam gasification and pyrolysis of biomass. Novel Rh catalysts (0.1wt%) supported on Mg-Ce-Zr-O-based mixed oxides modified by alkaline-earth, rare earth, and transition metal ions, having the general formula Mg-Ce-Zr-X-O (where X stands for La, Sr, Ba, Ca and Zn) were systematically studied. The physicochemical properties of the catalysts were evaluated using complementary bulk and surface characterization techniques, such as BET, XPS, in situ XRD, TEM/SAED and SEM/EDX. Transient techniques including H₂-TPR, TPD-CO₂ and TPD-NH₃ were employed in order to characterize redox behavior, surface basicity, and surface acidity of support, respectively. Among the catalysts examined, a 0.1wt% Rh/40Mg-20Ce-20Zr-20La-O was found to exhibit the highest hydrogen product yield, specific H₂ production rate (μmol/m²min), and the lowest CO/CO₂ product ratio (575–730°C), even when compared to a Ni-based commercial steam reforming of tars catalyst. At 655°C, a H₂ yield of ∼95% and a specific reaction rate of 100μmolH₂/m²min were obtained for a feed containing 0.5vol% phenol and 40vol% H₂O at a gas hourly space velocity of ∼80,000h⁻¹. This activity behavior is correlated with the largest concentration of basic sites and labile oxygen species (μmol/m²), and also with the largest acid/base site ratio present in the 40Mg-20Ce-20Zr-20La-O support composition. Steam was also found to be an efficient reagent for the removal of carbonaceous deposits (e.g., C_xH_y) formed on the catalyst surface during phenol steam reforming. The H/C atom compositional ratio of the carbonaceous deposits was found to depend on reaction temperature.

Keywords: Phenol steam reforming; Supported Rh catalysts; MgO-based solid supports; In situ; XRD; X-ray photoelectron spectroscopy; High resolution transmission electron microscopy; H; ₂; -TPR

Electrochemical activity of ruthenium and iridium based catalysts for oxygen evolution reaction by N. Mamaca; E. Mayousse; S. Arrii-Clacens; T.W. Napporn; K. Servat; N. Guillet; K.B. Kokoh (pp. 376-380).

Display Omitted► Ru- and Ir-based materials synthesized by Pechini–Adams method. ► Anode catalysts prepared free from carbon substrate. ► A single 5cm² PEM Water electrolysis. ► Good activity of Ru_xIr1−_xO₂ anodes towards OER.Powders of ruthenium and iridium-based materials were synthesized by the thermal decomposition process. The suitable heat treatment of the polymeric precursors allowed to recover metal oxides free from organic carbon, which can be oxidized to carbon dioxide during H₂O splitting at elevated potentials. The materials were examined by various physicochemical techniques in order to understand their electrochemical behavior as anodes in a 5cm² single proton exchange membrane water electrolyzer. Although the presence of Ir in the electrocatalyst composition contributes undoubtedly to its stability against ruthenium dissolution and the Faradaic efficiency of the PEM electrolysis cell, its great amount increases the overpotential value. The activity of the home made Ru_xIr1−_xO₂ anodes towards the oxygen evolution reaction occurs at ca. 1.5V at 25°C.

Keywords: Water electrolysis; Iridium; Ruthenium based electrocatalysts; Metal oxides; Pechini–Adams

Superior activity of MnO_x-CeO₂/TiO₂ catalyst for catalytic oxidation of elemental mercury at low flue gas temperatures by Hailong Li; Chang-Yu Wu; Ying Li; Junying Zhang (pp. 381-388).

Display Omitted► The combination of MnO_x and CeO₂ resulted in significant synergy for Hg⁰ oxidation. ► The MnO_x-CeO₂/TiO₂ catalyst was highly active for Hg⁰ oxidation even under SCR condition. ► NH₃ consumed surface oxygen and limited Hg⁰ adsorption, hence inhibited Hg⁰ oxidation. ► The deactivation of Hg⁰ oxidation by NH₃ could be completely recovered after stopping NH₃.TiO₂ supported Mn-Ce mixed oxides (Mn-Ce/Ti) synthesized by an ultrasound-assisted impregnation method were employed to oxidize elemental mercury (Hg⁰) at low temperatures in simulated low-rank (sub-bituminous and lignite) coal combustion flue gas and corresponding selective catalytic reduction (SCR) flue gas. The catalysts were characterized by BET surface area analysis, X-ray diffraction (XRD) measurement and X-ray photoelectron spectroscopy (XPS) analysis. The combination of MnO_x and CeO₂ resulted in significant synergy for Hg⁰ oxidation. The Mn-Ce/Ti catalyst was highly active for Hg⁰ oxidation at low temperatures (150–250°C) under both simulated flue gas and SCR flue gas. The dominance of Mn⁴⁺ and the presence of Ce³⁺ on the Mn-Ce/Ti catalyst were responsible for its excellent catalytic performance. Hg⁰ oxidation on the Mn-Ce/Ti catalyst likely followed the Langmuir–Hinshelwood mechanism, where reactive species on catalyst surface react with adjacently adsorbed Hg⁰ to form Hg²⁺. NH₃ consumed the surface oxygen and limited the adsorption of Hg⁰, hence inhibiting Hg⁰ oxidation over Mn-Ce/Ti catalyst. However, once NH₃ was cut off, the inhibited mercury oxidation activity could be completely recovered in the presence of O₂. This study revealed the possibility of simultaneously oxidizing Hg⁰ and reducing NO_x at low flue gas temperatures. Such knowledge is of fundamental importance in developing effective and economical mercury and NO_x control technologies for coal-fired power plants.

Keywords: Mercury; Manganese oxide; Cerium oxide; Catalyst; Coal combustion

Improvement of photocatalytic activity of TiO₂ nanoparticles on selectively reconstructed layered double hydroxide by Ruijuan Lu; Xin Xu; Jiapeng Chang; Yue Zhu; Sailong Xu; Fazhi Zhang (pp. 389-396).

Display Omitted► Supported TiO₂ nanoparticles with a highly dispersion were fabricated. ► Using the selectively reconstructed layered double hydroxide as a precursor. ► It showed excellent photocatalytic activity for degradation of methylene blue. ► The heterojunction nanostructure formed between TiO₂ nanoparticle and LDH support. ► The support's skeleton Cu²⁺ can improve the photocatalytic activity.Supported TiO₂ nanoparticles have been successfully fabricated by selective reconstruction of a Cu²⁺, Mg²⁺, Al³⁺, Ti⁴⁺-containing layered double hydroxide (CuMgAlTi-LDH) precursor, synthesized by coprecipitation, through calcination and rehydration process. A systematic investigation of the structural characterization and the photodegradation tests of methylene blue (MB) dye molecules from solution under both UV and visible light irradiation for the resulting TiO₂/CuMgAl-RLDH sample were carried out. Anatase-type TiO₂ nanoparticles are found to be homogeneously distributed on the surface of the selectively reconstructed CuMgAl-RLDH support. And the direct evidence for the surface TiO₂/LDH heterojunction formed on CuMgAl-RLDH is presented. For MB photodegradation under UV light or visible light illumination, TiO₂/CuMgAl-RLDH sample has superior photocatalytic properties to the rehydrated single phase R-TiO₂, the physical mixture of R-TiO₂ and CuMgAl-RLDH, the composite CuTi/MgAl-RLDH synthesized by the rehydration of mixture of MgAl-MMO and CuTi-MMO, and the TiO₂/MgAl-RLDH prepared under the same procedure as TiO₂/CuMgAl-RLDH without containing Cu ions. The skeleton Cu²⁺ ions dispersed in the mainlayer of CuMgAl-RLDH support can enable the photocatalytic activity for MB photodegradation. The TiO₂/LDH heterojunction nanostructure is proposed to contribute the efficient spatial separation between the photogenerated electrons and holes, which can concomitantly improve the photocatalytic activity. Our method provides a novel approach to fabricate new modes of load-type doped semiconductor photocatalysts which are both active under illumination by UV and visible light.

Keywords: TiO; ₂; Photocatalysis; Layered double hydroxide; Junction; Doping

Water splitting on Rhodamine-B dye sensitized Co-doped TiO₂ catalyst under visible light by Thi Thu Le; M. Shaheer Akhtar; Dong Min Park; Jang Choon Lee; O-Bong Yang (pp. 397-401).

Display Omitted► Rhodamine B (Rh B) dye sensitized Co doped TiO₂ (Co/TiO₂) materials was prepared for photocatalytic water splitting under visible light. ► Rh B-Co/TiO₂ obtains a strong absorbance edge band at max. absorbance 550nm with lower band gap of 2.58eV. ► Water splitting with Rh B-Co/TiO₂ catalysts achieved nearly stoichiometric evolution of H₂ and O₂ evolution of ∼227.3μmol/g-catal/h and ∼98.9μmol/g-catal/h. ► 6 times higher H₂ evolution obtains as compared with Co/TiO₂ catalysts.An effective rhodamine B (Rh B) dye sensitized Co doped TiO₂ (Co/TiO₂) materials was prepared by simple physical absorption for photocatalytic water splitting under visible light. The prepared Rh B-Co/TiO₂ materials showed a strong absorbance edge band in the range of 450–600nm (max. absorbance at 550nm) and estimated a moderate band gap of 2.58eV, which lowered than that of Co/TiO₂ (2.75eV). Rh B-Co/TiO₂ catalysts showed the high activity towards photocatalytic water splitting under visible light irradiation. The reaction with Rh B-Co/TiO₂ catalysts achieved a nearly stoichiometic evolution of H₂ and O₂ evolution of ∼227.3μmol/g-catal/h and ∼98.9μmol/g-catal/h, respectively, which is 6 times higher than that of H₂ evolution (∼37.67μmol/g-catal/h) over Co/TiO₂ catalysts. The enhanced water splitting reaction may be facilitated by the absorbed Rh B near to Co atom. This synergic effect between the Rh B and Co is crucial to the water splitting reaction.

Keywords: TiO; ₂; nanoparticles; Rhodamine B dye; Dye sensitization; Photocatalyst; Water splitting

Highly active and reusable palladium nanoparticle catalyst stabilized by polydimethylsiloxane for hydrogenation of aromatic compounds in supercritical carbon dioxide by Hsing-Jung Chen; Hsin-Wang Liu; Weisheng Liao; Horng-Bin Pan; Chien M. Wai; Kong-Hwa Chiu; Jen-Fon Jen (pp. 402-408).

Display Omitted► The detoxification of PCBs and PAHs method can be achieved through Pd/PDMS-catalyzed hydrogenation in sc-CO₂ under mild conditions. And supercritical technique is eco-friendly and efficient. ► The Pd/PDMS catalyst is easy to prepare and clean, and can be reused without losing activity. ► The Pd nanoparticles show good dispersion in PDMS support. The Pd/PDMS catalyst is similar to a homogeneous catalysis environment in sc-CO₂. ► Reactants can contact more active site due to the high swelling ability of PDMS polymers in sc-CO₂. ► PDMS support shows good absorption and diffusion due to the strong interaction between PDMS and hydrophobic reactants.This study describes a hydrogenation method for degrading polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) in supercritical carbon dioxide catalyzed by palladium nanoparticles stabilized in polydimethylsiloxane (Pd/PDMS). The process of synthesizing metal nanoparticles embedded in PDMS polymers involves the preparation of a homogenous mixture of metal salt, silicone elastomer, and a curing agent, followed by hydrogen reduction. PCBs and PAHs can be effectively hydrogenated to saturated hydrocarbons with greater than 99% efficiency in an hour under 200atm of CO₂ containing 10atm of H₂ at 313K using Pd/PDMS catalysts. The proposed Pd/PDMS catalysts can be reused without losing their activity and are significantly more active than commercial catalysts and a previously reported Pd nanoparticle catalyst stabilized in high-density polyethylene.

Keywords: Polychlorinated biphenyls; Polycyclic aromatic hydrocarbons; Supercritical carbon dioxide; Polydimethylsiloxane; Catalytic hydrogenation

Red phosphorus: An elemental photocatalyst for hydrogen formation from water by Feng Wang; Wilson Kwok Hung Ng; Jimmy C. Yu; Haojun Zhu; Chuanhao Li; Lei Zhang; Zhifeng Liu; Quan Li (pp. 409-414).

Display Omitted► A new property of red phosphorus for photocatalytic hydrogen formation from water has been discovered. ► H₂ was formed from the reduction of water by photogenerated electrons. ► Theoretical calculations indicated that the reduction of water by photogenerated electrons would be energetically possible. ► A P-type semicondutor behavior of red phosphorus was observed.A novel property of red phosphorus for visible light driven photocatalytic H₂ formation from water by photogenerated electrons has been discovered. The detection of hydroxyl radicals and results from photoconductivity measurements confirmed the photogeneration of electrons and holes. Theoretical calculations also indicated that the reduction of water by photogenerated electrons would be energetically possible. A P-type semiconductor behavior of red phosphorus was observed. Our findings may provide insights for developing phosphorus-based photocatalysts.

Keywords: Elemental photocatalyst; Hydrogen formation; Red phosphorus; Semiconductor

Modelling the kinetics of NO oxidation and NO_x storage over platinum, ceria and ceria zirconia by Kirsten Leistner; André Nicolle; Patrick Da Costa (pp. 415-423).

The effect of zirconium content on NO oxidation over Ce_xZr1−_xO₂.Display Omitted► Microkinetic parameters of NO_x oxidation/storage over ceria. ► Impact of zirconium content on NSR kinetics of Ce_xZr1−_xO₂. ► Modelling NO_x oxidation/storage over Pt/CeO₂.The kinetics of NO_x oxidation and storage were studied over Pt/Al₂O₃, Ce_xZr1−_xO₂ and Pt/CeO₂. A detailed kinetic mechanism involving lumped nitrate and nitrite species was proposed for the interaction of NO_x and O₂ with ceria(–zirconia) and its parameters estimated using oxidation and adsorption/desorption experiments. Important trends in the behaviour of ceria–zirconia catalysts ( x=0–0.84), platinum and Pt/CeO₂ were reproduced over a wide range of temperatures. Thus zirconium affects redox behaviour of the oxide, ultimately decreasing its ability to oxidise NO to NO₂. NO_x storage is described via the accumulation of nitrates on the oxide surface. Oxidation and storage over Pt/CeO₂ can be reproduced by fitting ceria and platinum-related parameters separately. While oxidation behaviour is mainly dictated by Pt, nitrate storage occurs on CeO₂ and is shown to be more efficient under a NO+O₂ flow than NO₂. However when considering an equal number of active sites, Pt/CeO₂ stores NO_x less efficiently than Pt/BaO/Al₂O₃.

Keywords: Ceria; Zirconia; Platinum; NO; _x; Kinetics

Kinetics of the NO/H₂/O₂ reactions on natural gas vehicle catalysts—Influence of Rh addition to Pd by Y. Renème; F. Dhainaut; P. Granger (pp. 424-432).

Display Omitted► Competition in favour of the NO/H₂ reaction on Rh/Al₂O₃ under lean conditions. ► Rh addition to Pd favours the NO/H₂ reaction but has a detrimental effect on the production of N₂. ► Importance to avoid direct interactions of Pd and Rh in NGV catalysts to get optimal efficiencies.This paper reports an extensive kinetic study of the NO/H₂ reaction on monometallic and bimetallic Pd and Rh based catalysts. The presence of oxygen in the feed has been examined and found to strongly alter the kinetic behaviour of noble metals according to the extent of the H₂/O₂ reaction which competes with the NO/H₂ reaction. Rate measurements have been discussed based on two different mechanisms which essentially differ from the nature of the NO dissociation step. On Pd/Al₂O₃, the predominant H₂/O₂ reaction depletes the surface hydrogen concentration inducing a dissociation step on a nearest-neighbour vacant site whereas hydrogen assists the dissociation of NO on Rh/Al₂O₃. Regarding Pd-Rh/Al₂O₃, none competitive adsorptions would likely occur with NO preferentially adsorbed on Rh. Such a result is supported by the weak partial pressure dependencies of the selectivity to N₂O formation similarly to Rh/Al₂O₃ which demonstrates that only Rh is involved in the formation of N₂ and N₂O on Pd-Rh/Al₂O₃. Nevertheless, it was found that Rh incorporation to Pd has a strong detrimental effect on the formation of nitrogen which suggests that structural might alter the adsorptive properties of rhodium in interaction with palladium.

Keywords: Kinetics; NO/H; ₂; reaction; N; ₂; O selectivity; Pd and Rh based catalysts; Reaction mechanism; Bimetallic catalysts

NO₂ adsorption on Fe- and Cu-zeolite catalysts: The effect of the catalyst red–ox state by Massimo Colombo; Isabella Nova; Enrico Tronconi (pp. 433-444).

Display Omitted► Fe-zeolite: dynamics of NO₂ adsorption influenced by the initial catalyst red–ox state. ► Oxidized sample: three moles of NO₂ consumed for one mole of NO released. ► Reduced sample: significantly higher NO evolution during NO₂ adsorption. ► The same qualitative results obtained also over a Cu-zeolite catalyst. ► NO₂ first oxidizes the catalyst, then formation of nitrates occurs.In the present work we investigate the adsorption of NO₂ onto a Fe- and a Cu-promoted zeolite SCR catalyst in the absence of gaseous water, with a particular focus on the effect of the catalyst red–ox state. For both catalytic systems, results from the analysis of the gas phase during step changes of the NO₂ concentration, combined with literature FTIR information, emphasize an important role of the catalyst red–ox state in the dynamics of NO₂ adsorption: the molar ratio of released NO to adsorbed NO₂ is close to 1/3 in the case of oxidized catalysts, in line with a two-steps mechanism leading to the formation of surface nitrates, but is greater when the catalyst is partially reduced. Furthermore the initial catalyst red–ox state influences the amount of nitrates that can be adsorbed on the catalyst surface, the pre-reduced sample exhibiting a greater storage capacity. The Cu-zeolite catalysts are able to store a greater amount of nitrates and are more easily reduced in comparison with the Fe-zeolite.

Keywords: Adsorption; Diesel exhaust aftertreatment; Nitrogen oxides; Urea SCR; Zeolite catalysts

Dual layer automotive ammonia oxidation catalysts: Experiments and computer simulation by A. Scheuer; W. Hauptmann; A. Drochner; J. Gieshoff; H. Vogel; M. Votsmeier (pp. 445-455).

Display Omitted► A bi-functional dual layer design improves selectivity of NH₃-oxidation catalysts. ► A mechanistic model for NH₃ oxidation on platinum is presented. ► Diffusion effects in the dual layer catalyst are studied by a 2-D numerical model. ► The model well reproduces the experimental results for the dual layer catalyst.Today, platinum based ammonia oxidation catalysts are applied in automotive exhaust systems to avoid ammonia slip from the SCR catalyst. In this paper we present a dual layer catalyst design with an additional SCR layer on top of the Pt/Al₂O₃ layer. Laboratory experiments show that the additional SCR layer significantly reduces NO formation, improves N₂ selectivity but also reduces the overall NH₃ conversion.A mechanistically based kinetic model for NH₃ oxidation on platinum is presented. The model is parameterised using experiments with a single layer Pt/Al₂O₃ catalyst and well describes the NH₃ conversion and the selectivities for the products N₂, N₂O and NO. Additionally NO oxidation to NO₂ is included in the model.Based on the mechanistic model for the platinum layer and a previously published model for the SCR layer, a 2-D model of the dual layer catalyst is set up. This model takes into account the diffusion and reaction in the two washcoat layers of one monolith channel. The 2-D model reproduces the experimental data well, with the mechanisms for the two layers parameterised in separate experiments and no additional parameters adjusted for the dual layer model.Finally, the model is used to study the effect of some design parameters such as catalyst size, NO oxidation capacity of the Pt-layer and the thickness or diffusion coefficient of the SCR layer.

Keywords: Catalysis; Automotive; Dual layer; Ammonia oxidation; Platinum

High efficiency production of substitute natural gas from biomass by Luc P.L.M. Rabou; Lex Bos (pp. 456-460).

Display Omitted► Production of SNG from biomass through gasification at 800–900°C. ► Conversion of biomass producer gas requires removal of 10ppmv thiophene. ► Benzene and ethylene must be converted to methane to obtain high efficiency. ► HDS of thiophene in biomass producer gas is possible at atmospheric pressure. ► HDS catalyst also promotes water–gas shift and hydrogenation of ethylene.The Energy research Centre of the Netherlands (ECN) is developing technology for the production of Substitute Natural Gas (SNG) from biomass with 70% efficiency. An essential step in the process is the removal of thiophene, while benzene and toluene must be retained and converted into methane. Experimental results are presented which show that thiophene can be reduced from 10ppmv to 0.1ppmv by commercial hydrodesulphurization (HDS) catalysts at atmospheric pressure. The catalysts also promote the water gas shift and hydrogenation reactions. The operating temperature of 550°C is too high and the Gas Hourly Space Velocity (GHSV) of 100h⁻¹ too low for practical application. Future SNG installations will operate at higher pressure, which should promote the catalytic activity at lower temperature and result in higher GHSV values. The catalyst used for conversion of benzene did work initially, but degraded within 50h.

Keywords: Biomass; Gasification; Methanation; Hydrodesulphurization; Hydrogenation

Controlled synthesis of highly active mesoporous Co₃O₄ polycrystals for low temperature CO oxidation by Yingjun Feng; Liang Li; Shufan Niu; Yan Qu; Qian Zhang; Yongsheng Li; Wenru Zhao; Hua Li; Jianlin Shi (pp. 461-466).

Display Omitted► Polycrystal mesoporous Co₃O₄ has been successfully fabricated using a simple but efficient controlled thermal decomposition method. ► The resulting nanosized Co₃O₄ crystallites connected together to form mesoporous structure. ► Material calcined at 300°C at a heating rate of 0.5°C/min possessed high surface area. ► It's full CO conversion can be reached at as low as −70°C.Polycrystalline mesoporous Co₃O₄ has been successfully fabricated using a simple but efficient controlled thermal decomposition approach and their catalytic activities for low temperature CO oxidation were evaluated. In such a synthesis, micrometer-sized polyhedral cobalt oxalate crystals were first prepared and used as precursor. Mesoporosity was then generated via the pyrolysis of the cobalt oxalate precursor and the resultant nano-sized Co₃O₄ crystallites connected together to form mesoporous structure within the original micrometer-sized particles. The as-prepared material by calcination at 300°C at a heating rate of 0.5°C/min possessed high surface area and showed extraordinarily high catalytic activity for low temperature CO oxidation, the full CO conversion can be achieved at as low as −70°C.

Keywords: Cobalt oxide; Catalyst; Mesoporous materials; CO oxidation

Investigation of catalytic mechanism of formaldehyde oxidation over three-dimensionally ordered macroporous Au/CeO₂ catalyst by Baocang Liu; Changyan Li; Yifei Zhang; Yang Liu; Wenting Hu; Qin Wang; Li Han; Jun Zhang (pp. 467-475).

Novel 3DOM Au/CeO₂ catalysts were created via a colloidal crystal template method coupled with a precursor complexion process, and their catalytic mechanism for enhanced HCHO catalytic oxidation was revealed in detail.Display Omitted► 3DOM Au/CeO₂ catalyst was created via a colloidal crystal template method coupled with a precursor complexion process. ► The catalytic mechanism of the catalyst for enhanced HCHO catalytic oxidation was revealed in detail. ► The weak absorption ability of CO₂ and the existence of Au active species in ionic and metal states in 3DOM Au/CeO₂ catalyst improve the catalytic activity. ► The carbonate and hydrocarbonate formed on the surface of 3DOM Au/CeO₂ catalyst may account for its deactivation.A colloidal crystal template method coupled with a precursor complexion process was developed to create three-dimensionally ordered macroporous (3DOM) Au/CeO₂ catalyst. The resultant Au/CeO₂ catalyst possesses well-defined 3DOM structure, and shows enhanced catalytic performance for formaldehyde (HCHO) oxidation with 100% HCHO conversion at ∼75°C. The catalytic mechanism of HCHO catalytic oxidation over 3DOM Au/CeO₂ catalyst was systematically investigated by means of gas chromatograph (GC), H₂-temperature programmed reduction (H₂-TPR), temperature programmed surface reaction (TPSR), CO₂-temperature programmed desorption (TPD), and Fourier transform infra-red (FT-IR) spectroscopy. GC results indicate that HCOOH intermediate is generated during HCHO catalytic oxidation. TPD and TPSR tests show that the weak absorption ability of CO₂ over 3DOM Au/CeO₂ catalyst and the existence of Au active species in ionic and metallic states in 3DOM Au/CeO₂ catalyst largely improve the catalytic activity, favoring the enhanced HCHO catalytic oxidation. FT-IR tests prove that the carbonate and hydrocarbonate formed on the surface of 3DOM Au/CeO₂ catalyst during HCHO catalytic oxidation may account for its deactivation. Based on the above investigation, a new catalytic mechanism of enhanced HCHO catalytic oxidation over 3DOM Au/CeO₂ catalyst is proposed. The mechanism may afford the scientific guidance for preparing high efficiency oxide supported noble metal catalysts and present a solution for solving their deactivation problem.

Keywords: Three-dimensionally ordered macroporous material; Au/CeO; ₂; catalyst; Formaldehyde oxidation; Catalytic mechanism

Synchrotron radiation PXRD investigation of V₂O₅/TiO₂ catalysts for 1,2-dichlorobenzene oxidation: Implication of structure modification by Hsi-Yan Chang; Shao-Pin Wang; Jen-Ray Chang; Hwo-Shuenn Sheu; Shin-Guang Shyu (pp. 476-484).

V₂O₅/TiO₂ activity can be enhanced by adding MoO₃ and introducing sulfur-containing compounds to the reaction system. MoO₃ disperses vanadia and forms MoV₂O₈ during the reaction, which plays critical roles in the activity enhancement.Display Omitted► Catalytic activity enhancement by adding MoO₃ and sulfur-containing compound. ► MoO₃ disperses vanadia and forms MoV₂O₈ during the reaction. ► Higher pre-exponential factors were observed. ► Structure change in vanadia species leads to reduction in apparent activation energy.V₂O₅/TiO₂ catalysts were prepared by depositing vanadia on nano-particles of anatase TiO₂ and tested for oxidation of 1,2-dichlorobenzene. Activity of the catalyst can be enhanced by adding MoO₃ to the catalysts and introducing sulfur-containing compounds to the reaction system. Kinetic studies indicate that addition of MoO₃ reduces the apparent activation energy slightly and increases the pre-exponential factors at reaction temperatures higher than 350°C; in contrast, introduction of sulfur-containing compounds only increases the pre-exponential factors. XRD and FT-IR results indicate that MoO₃ disperses vanadia species and induces formation of crystalline MoV₂O₈ during the reaction, whereas introduction of sulfur-containing compounds leads to no significant structure change. Based on these characterizations and analyses of the kinetic results, we suggest that increased catalyst acidity results in higher pre-exponential factors, while structure change in vanadia species leads to reduction in apparent activation energy.

Keywords: Oxidation reaction; PXRD; FT-IR; 1,2-Dichlorobenzene; Rietveld refinement; V; ₂; O; ₅; /TiO; ₂

Photoelectrocatalytic degradation of refractory organic compounds enhanced by a photocatalytic fuel cell by Yanbiao Liu; Jinhua Li; Baoxue Zhou; Shubin Lv; Xuejin Li; Hongchong Chen; Quanpeng Chen; Weimin Cai (pp. 485-491).

Display Omitted► We established a novel composite system for efficient organic pollutant treatment. ► The removal efficiency of organics was evidently enhanced by the fuel cell system. ► Various important parameters influencing the removal of organics were studied.A novel composite photoelectrocatalytic system, composed of a photoelectrocatalytic reactor and a photocatalytic fuel cell (PFC), was established with the aim to efficiently degrade refractory organic compounds. The PFC is device, in which the organic “substrates” were photodecomposed and the chemical energy of organic “substrates” was converted into electrical energy simultaneously. Within the composite system, the electricity produced by PFC, rather than external power supply, was exerted on the photoelectrocatalytic reactor to serve as potential bias. The organic compound degradation performance and affecting factors of the composite system were also studied. The experimental results demonstrate that the removal efficiency of organic compound in the photoelectrocatalytic reactor was evidently enhanced by the PFC system. The kinetic constant of the photoelectrocatalytic process was found to be ∼1.75 times that of the pure photocatalytic process. Furthermore, the performance of the photoelectrocatalytic reactor was found to increase with the illumination area (of the anode) of PFC and decrease with the external resistor and electrolyte concentration. The category and concentration of the substrate in PFC system were also key factors influencing the efficiency of organic compound removal in the photoelectrocatalytic reactor. The composite system provides a novel way for utilizing of the electrical energy generated from the PFC system and has potential applications for the treatment of various refractory organic pollutants.

Keywords: Photoelectrocatalysis; TiO; ₂; nanotube array; Photocatalytic fuel cell

Preparation of meso-macroporous carbon nanotube-alumina composite monoliths and their application to the preferential oxidation of CO in hydrogen-rich gases by Suhong Lu; Yuan Liu (pp. 492-501).

.Display Omitted► CNT-Al₂O₃ monoliths possess interconnected macropores and meso-pores. ► Carbon nanotubes can be uniformly distributed in the alumina matrix. ► CNT content and calcination temperature affect on mesopore structure, mechanical strength and thermal conductivity. ► CNT-Al₂O₃-supported Pt-Ni shows good catalytic performance for CO preferential oxidation.A series of carbon nanotube (CNT)-alumina composite monoliths with meso-macroporous structures were successfully synthesized by imbibing macroporous monolithic polystyrene foams with carbon nanotube-alumina hydrosols. These composite monoliths possessed interconnected spherical macropores that mainly ranged in 10–40μm and adjustable mesopores of several nanometers. CNTs were uniformly dispersed throughout the alumina matrix. The CNT content and the calcination temperature markedly influenced the mesoporous structure, mechanical strength and thermal conductivity of the composite monoliths, but they did not significantly influence the phase transitions of alumina. The Pt-Ni/CNT-Al₂O₃ monoliths that were calcined at 1300°C exhibited high activity and selectivity with small Pt loading of 0.75wt.% for the preferential oxidation of CO. The residual concentration of CO was purified to less than 100ppm in the temperature range of 120–180°C in CO₂ and water-containing hydrogen-rich gases at a volume space velocity of 10,400h⁻¹. This type of composite monolith could potentially be used as a catalyst support for many different reactions.

Keywords: Carbon nanotube; Alumina; Composite; Monolith; Preferential oxidation

Facile synthesis of pure TiO₂(B) nanofibers doped with gold nanoparticles and solar photocatalytic activities by Jesty Thomas; Minjoong Yoon (pp. 502-508).

.Display Omitted► We develop a new facile synthetic route for purely crystallized TiO₂(B) nanofibers. ► We examine the optoelectronic natures of free and Au-doped TiO₂(B) nanofibers (Au-T_BNF). ► Au-doping increases visible light absorption and long-lived charge-separation. ► The solar photocatalytic efficiency of Au-T_BNF is greater than that of anatase analogs. ► Au-T_BNF would be very useful as an environmentally sustainable solar photocatalysts.Pure and highly crystallized gold nanoparticles-doped-TiO₂(B) nanofibers (Au-T_BNFs), with thickness of 50–200nm and length of several microns, were successfully synthesized by combination of low-temperature (150°C) hydrothermal reaction of titanium (IV) isopropoxide (Ti[OC₃H₇]₄) and sonication of the ensued precipitate with gold nanoparticles followed by post-heat treatment at 300°C. Formation of pure TiO₂(B) was confirmed by X-ray diffraction, high resolution transmission electron microscopy and Raman spectroscopy. The UV–vis diffuse reflectance spectra (DRS) of Au–TiO₂(B) nanofibers exhibited surface-state absorption beyond 400nm with band gap energy at 2.94eV and broad gold plasma resonance band around 550nm. The photoluminescence (PL) emission spectra of the Au-T_BNFs exhibited structural emission band around 410nm with shoulders around 464nm and 540nm. Analysis of these optical properties revealed that the surface state absorption is attributed to the indirect transition. These results suggest that coupling of the surface charge carriers with the lattice phonon of Au-T_BNFs is so strong that the charge recombination is mostly nonradiative as supported by the significantly quenched emission of Au-T_BNFs as compared to that of free T_BNFs. These optoelectronic properties were well correlated with highly efficient solar photocatalytic activities of Au-T_BNFs for oxidation of methylene blue (MB).

Keywords: TiO; ₂; (B) nanofibers; Gold nanoparticles; Doping; Solar photocatalysis; Visible light photocatalysts; Optoelectronic properties

Quantitative determination of average rhodium oxidation state by a simple XANES analysis by Ken-ichi Shimizu; Tomonori Oda; Yoshinori Sakamoto; Yuichi Kamiya; Hisao Yoshida; Atsushi Satsuma (pp. 509-514).

Display Omitted► Rh L₃-edge XANES analysis as a simple method to quantify the average Rh oxidation state. ► A linear relationship between the Rh oxidation state and the white line intensity. ► Characterized by CO-titration, X-ray diffraction, and Rh K-edge XAS supports the conclusion. ► The effect of the oxidation state on the Rh₂O_x/SiO₂-catalysed CO oxidation is demonstrated.Quantitative determination of average rhodium oxidation state for supported rhodium catalyst was examined by using Rh L₃-edge XANES (X-ray absorption near-edge structure) spectra. A series of Rh-loaded SiO₂ catalysts (Rh₂O_x/SiO₂) containing different amount of Rh metal and Rh₂O₃ phases were prepared, and the average oxidation number ( x) was determined by the amount of CO₂ formed during CO reduction treatment as the final step of catalyst preparation. L₃-edge XANES spectra of these samples were recorded, and the white line area intensity of the spectra was evaluated. A good linear relationship was confirmed between the white line area intensity and the average oxidation number ( x), indicating that the oxidation state of Rh species in structurally unknown Rh samples could be quantitatively determined by a simple L₃-edge XANES analysis. The effect of the oxidation number ( x) on the Rh₂O_x/SiO₂-catalysed CO oxidation was discussed, in order to demonstrate a utility of this method in a catalytic study.

Keywords: XANES; Rhodium; Characterization; Oxidation state; Heterogeneous catalysis

Oxygen reduction reaction (ORR) activity and durability of carbon supported PtM (Co, Ni, Cu) alloys: Influence of particle size and non-noble metals by Kaushik Jayasayee; J.A. Rob Van Veen; Thirugnasambandam G. Manivasagam; Serdar Celebi; Emiel J.M. Hensen; Frank A. de Bruijn (pp. 515-526).

Display Omitted► Fresh non-noble metal-rich alloys show enhanced oxygen reduction activity. ► The specific activity of the aged Pt/C and PtM/C annealed at a similar temperature is quite comparable. ► The alloying effect is almost completely lost due to dissolution of about 90–95at% non-noble metals. ► Alloy surface only consists of Pt after the durability tests, and only a weak particle-size effect remains.Carbon supported platinum and platinum alloys (PtCo, PtNi and PtCu) for PEMFC cathodes were prepared and studied for their oxygen reduction reaction activity and durability under potential cycling at 80°C in 0.5M HClO₄. Catalysts with different metal alloy composition and particle size were synthesized by annealing at different temperatures to discriminate between the effects of alloying and particle size on the electrocatalytic activity and durability. XRD was used for the structural characterization of pristine catalysts, while the bulk compositions were analyzed by EDS before and after durability tests. XPS was employed to determine the surface composition of selected alloys after durability tests. The particle size of the fresh and aged catalysts was determined by TEM. Rapid dealloying, particularly from non-noble metal rich alloys, was already witnessed for the alloys potentially cycled at room temperature. Significant particle growth depending on the initial particle size was observed for both Pt and Pt alloys after the durability tests. For the alloys with similar initial particle size, the initial electrocatalytic activity depends on the initial alloy composition. Although a 3-fold enhancement in the ORR activity was observed for the non-noble metal rich alloys after initial dealloying, the specific activity of Pt and Pt alloys becomes quite similar at the end of the durability tests. Annealing of Pt/C and Pt alloys at 950°C results in catalysts with the highest specific and mass activity and with the highest stability.

Keywords: Pt alloys; ORR activity; PEMFC; Fuel cells; Durability

Removal of natural organic matter for drinking water production by Al/Fe-PILC-catalyzed wet peroxide oxidation: Effect of the catalyst preparation from concentrated precursors by Luis Alejandro Galeano; Pedro Fernando Bravo; Cristian Darío Luna; Miguel Ángel Vicente; Antonio Gil (pp. 527-535).

.Display Omitted► Preparation of Al/Fe-pillared clays from concentrated precursors is evaluated. ► An improved hydrolysis ratio for concentrated Al/Fe metal precursors is found. ► Pillaring in ethanol suspension is less susceptible against the clay concentration. ► The clay catalysts display high NOM removals by CWPO for drinking water production. ► High activity and catalyst stability are shown even under pH of reaction 7.5.Catalytic wet peroxide oxidation (CWPO) has been assessed at semi-batch lab scale for the removal of natural organic matter (NOM) from raw surface water currently employed as feedstock in a drinking water treatment's plant. The peroxide solution has been stepwise added and its catalytic activation carried out by Al/Fe-pillared clays prepared from concentrated or diluted both, metal precursor solutions and clay suspensions (aqueous or ethanolic). An improved hydrolysis ratio (OH/(Al+Fe)) of 1.6 was found by Ferron analyses for the preparation of the concentrated metal precursor ([Al+Fe]=0.628mol/dm³), without significant metal loss by precipitation. Increased concentration of the pillaring precursor solution led to: (i) slightly decreased and (ii) more broadly distributed XRD-basal spacings, but also (iii) higher cationic compensation on the starting clay. Ethanol as suspension medium enabled the oligomer intercalation to be less susceptible against the clay concentration. It was achieved up to 96% of chemical oxygen demand (COD) removal in 4h and total color removal in less than 45min of reaction for a selected catalyst, under very mild conditions of room temperature and atmospheric pressure. The clay catalysts displayed high chemical stability against iron leaching. In addition, the solid prepared from the concentrated metal precursor in a 25% (w/v) ethanolic suspension successfully performed in a high demanding catalytic test, which involved very high humic substrate-to-catalyst ratio, prolonged time of reaction (24h) and close to neutral pH of reaction (7.5), identical to that featured by the raw surface water.

Keywords: CWPO; Natural organic matter; Pillared clay; Drinking water; Humic substances

Hydrogen from ethylene glycol by supercritical water reforming using noble and base metal catalysts by D.J.M. de Vlieger; A.G. Chakinala; L. Lefferts; S.R.A. Kersten; K. Seshan; D.W.F. Brilman (pp. 536-544).

Display Omitted► Catalytic reforming of ethylene glycol in supercritical water is studied in the presence Pt based mono- and bi-metallic catalysts (PtNi). ► Pt catalyst showed the highest hydrogen yields compared to Ir and Ni. ► Addition of Ni to the Pt in a PtNi bimetallic catalyst improved hydrogen yields by suppressing methane formation. ► Bimetallic catalysts were found to be more active and stable than the mono-metallic catalysts.Catalytic reforming of ethylene glycol (5 and 15wt%) in supercritical water (450°C and 250bar) in the presence of alumina supported mono- and bi-metallic catalysts based on Ir, Pt and Ni was studied. Pt catalyst showed the highest hydrogen yields compared to Ir and Ni. Varying the Pt loading (0.3–1.5wt%) showed that the intrinsic reforming activities improved with decreasing Pt loadings. However, a lower Pt loading had a large negative effect on the H₂ selectivity and catalyst stability. It was found that the presence of Ni in a Pt–Ni bimetallic catalyst improved hydrogen yields by suppressing methane formation. Moreover, the presence of Ni also enhanced catalyst stability. Results reported here were obtained at WHSV of 18h⁻¹. The Pt–Ni/Al₂O₃ having a total metal loading of 1.5wt% (molar ratio Pt:Ni=1), is identified as a promising catalyst for the reforming of ethylene glycol in supercritical water and may prove suitable for various other SCWG applications.

Keywords: Sustainable; Renewable; Supercritical water; Reforming; Hydrogen; Catalysts; Ethylene glycol

Mild solar photo-Fenton: An effective tool for the removal of Fusarium from simulated municipal effluents by M. Inmaculada Polo-López; Irene García-Fernández; Theodora Velegraki; Athanasia Katsoni; Isabel Oller; Dionissios Mantzavinos; Pilar Fernández-Ibáñez (pp. 545-554).

. Sources of hydroxyl radicals for fungal spore under solar photo-Fenton process include (a) external photo-Fenton process with exogenous iron, and (b) internal Fenton reactions with endogenous iron.Display Omitted► Sunlight coupled with iron ions and/or hydrogen peroxide to inactivate F. solani in municipal wastewater was studied. ► Biology of the microorganism is critical to evaluate the disinfection efficiency and mechanisms. ► Mild solar photo-Fenton may be an alternative wastewater treatment for the removal of NOM and pathogens.In this work, the efficacy of natural solar radiation (up to 21.1kJ/L of UV energy dose) combined with homogeneous iron (5 and 10mg/L Fe²⁺) and/or hydrogen peroxide (10 and 20mg/L) to treat a simulated municipal effluent in a solar bottle reactor was assessed. Emphasis was given on the inactivation of resistant spores with Fusarium solani serving as the test species in a matrix containing 25mg/L of dissolved organic carbon, 65mg/L of inorganic carbon and pH about 8. Processes like dark Fenton oxidation (5mg/L Fe²⁺ and 10mg/L H₂O₂ at pH 3), solar radiation alone (at 21.1kJ/L and pH 3–8) and H₂O₂ oxidation alone (up to 20mg/L in the dark) led to no or inadequate disinfection, thus showing the resistance of F. solani. Solar irradiation in the presence of 10mg/L peroxide led to complete inactivation (i.e. ≤2CFU/mL which is the detection limit) with 11.9kJ/L at pH 3 and 16.9kJ/L at pH 4–8, but no mineralization occurred. When the process was added 5mg/L Fe²⁺, complete inactivation required 17.1kJ/L at pH 3 but this was accompanied by 36% mineralization. Interestingly, doubling the concentration iron and peroxide hindered inactivation but promoted mineralization; these results demonstrate a competitive effect between spores and the effluent organic matter for hydrogen peroxide, hydroxyl radicals and other ROS and highlight the importance of the nature of the microorganism. Finally, the implications for wastewater treatment are also discussed.

Keywords: Solar disinfection; Fusarium solani; Mineralization; Wastewater; Competition

Synthesis of vanillin in water by TiO₂ photocatalysis by Vincenzo Augugliaro; Giovanni Camera-Roda; Vittorio Loddo; Giovanni Palmisano; Leonardo Palmisano; Francesco Parrino; Maria Angela Puma (pp. 555-561).

The photoproduction of vanillin is reported in aqueous medium starting from trans-ferulic acid, isoeugenol, eugenol or vanillyl alcohol by using both commercial and home prepared TiO₂ samples as the photocatalysts and batch photoreactors. Crystals of vanillin were obtained by pervaporation under ambient temperature with a high degree of purity.Display Omitted► Photocatalytic synthesis of vanillin. ► Trans-ferulic acid, isoeugenol, eugenol, vanillyl alcohol, used as substrates. ► Commercial and home prepared TiO₂ samples for partial photo-oxidation.The photoproduction of vanillin is studied in aqueous medium starting from trans-ferulic acid, isoeugenol, eugenol or vanillyl alcohol by using both commercial and home prepared TiO₂ samples as photocatalysts and batch Pyrex photoreactors. The photo-oxidation at room temperature of these compounds produces vanillin with a selectivity ranging from 1.4 to 21mol% with respect to the converted substrate. An investigation on the intermediates was performed in the case of trans-ferulic acid; for this substrate the most important intermediates were homovanillic acid, vanillyl mandelic acid, trans-caffeic acid, formic acid, acetic acid, and oxalic acid. The carbon mass balance, including CO₂ derived from the mineralization, was made for all of the substrates at irradiation times corresponding to the highest selectivity to vanillin. High closure of the carbon balance was obtained with vanillyl alcohol (ca. 90%) and trans-ferulic acid (ca. 80%).

Keywords: Titanium dioxide; Photocatalysis; Vanillin; Partial oxidation

A non-NH₃ pathway for NO_x conversion in coupled LNT-SCR systems by Jin Wang; Yaying Ji; Zhengwang He; Mark Crocker; Mark Dearth; Robert W. McCabe (pp. 562-570).

Display Omitted► NO_x reduction was studied in a combined LNT-SCR system. ► Propene and ethene function as NO_x reductants over the SCR catalyst. ► NH₃ and propene can co-adsorb in the SCR catalyst. ► Contributions of NH₃ and C₃H₆ to NO_x conversion are additive under lean-rich cycling.NO_x storage-reduction experiments were performed using a coupled LNT-SCR system consisting of a low-precious metal loaded Pt/Rh LNT catalyst and a commercial Cu–zeolite SCR catalyst. Cycling experiments revealed that when a CO+H₂+C₃H₆ mixture or C₃H₆ by itself was used as the reductant, the NO_x conversion over the SCR catalyst exceeded the conversion of NH₃ over the same catalyst. This is explained by the presence of propene, which slipped through the LNT catalyst and reacted with the LNT NO_x slip. Separate experiments, conducted under continuous flow and lean-rich cycling conditions, confirmed the ability of propene, as well as ethene, to function as a NO_x reductant over the SCR catalyst. Cycling experiments also revealed that the SCR catalyst was able to store propene, such that NO_x reduction by stored propene continued into the lean phase (after the switch from rich conditions). According to adsorption experiments, significant co-adsorption of NH₃ and propene occured in the SCR catalyst, while under lean-rich cycling conditions the contributions of NH₃ and C₃H₆ to NO_x conversion were found to be essentially additive. These findings suggest that under actual driving conditions, NO_x reduction by non-NH₃ reductants (olefins and possibly other hydrocarbons) in the SCR catalyst can contribute to the mitigation of lean and rich phase NO_x.

Keywords: LNT-SCR; Lean NO; _x; trap; NO; _x; storage/reduction catalyst; SCR; Hydrocarbon

A hierarchically structured and multifunctional membrane for water treatment by Hongwei Bai; Zhaoyang Liu; Darren Delai Sun (pp. 571-577).

Display Omitted► The hierarchical TiO₂/ZnO nanomaterials were fabricated. ► A multifunctional membrane was assembled by using these hierarchical TiO₂/ZnO nanomaterials. ► This multifunctional membrane shows good properties in high photocatalytic activity, high flux and high antibacterial capacity. ► This multifunctional membrane is a good candidate for producing clean water.Currently, the biggest challenge for filtration membrane application is the severe membrane fouling problem, which consequently results in low flux and high energy cost. Herein, a novel kind of multifunctional membrane was fabricated via integrating the advantages of conventional polymer membrane as supporting layer and “forest” like hierarchically structured TiO₂/ZnO nanomaterials as functional layer. This membrane has shown multifunctional properties, such as, high photocatalytic activity, high flux and high antibacterial capacity, which make it as a good candidate to tackle the challenge of producing clean water at a constant high flux with no membrane fouling problem and energy saving manner. The outstanding performance of this novel membrane would bring enough benefits to filtration membrane industry for clean water production and environmental protection.

Keywords: Antibacterial; Hierarchical; Membrane; Photocatalytic activity; Permeate flux

Design and high efficient photoelectric-synergistic catalytic oxidation activity of 2D macroporous SNO₂/1D TiO₂ nanotubes by Peiqiang Li; Guohua Zhao; Mingfang Li; Tongcheng Cao; Xiao Cui; Dongming Li (pp. 578-585).

Display Omitted► 2D macroporous SnO₂/1D TiO₂ NTs prepared using the soft template method. ► Prepared anode presents excellent photocatalytic and electrocatalytic properties. ► 2D macroporous SnO₂/1D TiO₂ NTs with synergistic photoelectrocatalytic function.A novel catalyst was constructed by assembling 1D TiO₂ nanotubes (TiO₂ NTs) photocatalyst and 2D macroporous SnO₂ electrocatalyst, which presents simultaneously the outstanding photocatalytic and electrocatalytic properties, and was applied to the photoelectric synergistic catalytic oxidation of biorefractory pollutants. Liquid crystal soft template was prepared by block copolymer self-assembly, and the macroporous SnO₂ membrane grew orderly on the TiO₂ NTs using the soft template by one-step assembly. The macroporous SnO₂ has the pore size distribution between 150 and 400nm, small particle size (14.2nm), and high loading amount (27.3gm⁻²). The band gap of the 2D macroporous SnO₂/TiO₂ NTs is 2.93eV. Compared with the general TiO₂ NTs and the SnO₂/TiO₂NTs, the 2D macroporous SnO₂/TiO₂ NTs possess better optical absorption and photocatalytic properties, with a photoelectric conversion efficiency of 35.2% at 365nm. Moreover, the hybrid anode presents smaller surface impedance and solution interface impedance, larger electrochemical surface absorption volume and lower electrochemical reaction activation energy. In the photoelectrocatalytic process, the 2D macroporous SnO₂/TiO₂ NTs exhibited higher removal rate for 2,4-dichlorophenoxyacetic acid, the initial instantaneous current efficiency was 100%, and COD removal rate reached 90.1% within 3h. The study showed that the intermediates was generated faster and removed quickly on the prepared catalyst.

Keywords: One-dimentional titanium oxide nanotubes; Two-dimentional macroporous SnO; ₂; Photoelectric-synergistic catalyst; 2,4-dichlorophenoxyacetic acid

Application of Ni supported over mixed Mg–Al oxides to crystal violet wet air oxidation: The role of the reaction conditions and the catalyst by Gabriel Ovejero; Araceli Rodríguez; Ana Vallet; Sylvius Willerich; Juan García (pp. 586-594).

Display Omitted► Ni supported over hydrotalcite calcined precursors as catalyst. ► Catalytic wet air oxidation in batch reactor for crystal violet removal. ► Effects of temperature, pressure, pH and initial dye concentration were tested. ► The catalyst proved to be stable and efficient for the dye degradation.This study explores the ability of nickel catalysts supported over Mg–Al mixed oxides (Ni/HT) by incipient wetness impregnation technique for the catalytic wet air oxidation of aqueous crystal violet solutions. The effect of operational conditions such as temperature, pressure, pH, presence of the catalyst and initial dye concentration has been tested. It has been demonstrated that Ni/HT is an efficient catalyst for the CWAO of crystal violet (CV) at mild reaction conditions. The reaction which was carried out at its natural pH, showed to be the most efficient when Ni/HT was employed. The catalyst does not lose any of its activity in the recycling experiments performed, when CV degradation is considered.

Keywords: Catalyst; Colour; Dye; Nickel; Wastewater

Dynamic changes on the surface during the calcination of rapid heat treated TiO₂ photocatalysts by Zs. Pap; É. Karácsonyi; Zs. Cegléd; A. Dombi; V. Danciu; I.C. Popescu; L. Baia; A. Oszkó; K. Mogyorósi (pp. 595-604).

Display Omitted► Rapid heat treatment results in high UV-activity photocatalysts. ► Surface purity determines the activity at 400°C. ► Surface anchored species influences the measured photoactivity. ► High UV activity for short/medium calcination times at 550 and 600°C. ► Special oxygen forms appear at the surface for the best catalysts.Titanium dioxide photocatalysts were prepared by a newly developed synthesis method that involves rapid heating with short, medium and long exposures of the sol–gel prepared amorphous starting materials (RHSE, RHME and RHLE series) at different temperatures and calcination times. These materials were characterized by various methods, such as XRD, TEM, DRS, IR, nitrogen adsorption and XPS techniques. The detailed study of these catalysts revealed that at low calcination temperatures (e.g. 400°C) the highest activity will be achieved if a long calcination (90–120min) is applied because of the surface purification from the deposited organics. At higher temperatures (e.g. 550°C) shorter calcination times (5–10min) proved to be effective to achieve high UV activity. At this temperature an unidentified oxygen type was detected from the O1s XPS of the samples which seems to be related to the presence of Ti³⁺. At 600°C both short (10min) and medium calcination (30–90min) times were found to be beneficial for the phenol degradation under UV irradiation due to the very effective sensitization (10min of calcination) and surface OH-group preservation (60min of calcination).

Keywords: Titania; Photocatalysis; Phenol; Rapid crystallization; Surface quality

Influence of H₂S on ZrO₂-based gasification gas clean-up catalysts: MeOH temperature-programmed reaction study by E. Inkeri Kauppi; E. Hanne Rönkkönen; Sanna M.K. Airaksinen; Søren B. Rasmussen; Miguel A. Bañares; A. Outi I. Krause (pp. 605-613).

Display Omitted► ZrO₂-based catalysts are active in tar removal during gasification gas clean-up. ► The effect of H₂S on catalyst activity differs for ZrO₂ and Y₂O₃-ZrO₂in comparison with SiO₂-ZrO₂. ► Study by characterization methods using MeOH and H₂S probes. ► Adsorption sites for H₂S differed for the three studied catalysts. ► Effect of H₂Son the activity during gas clean-up was correlated with the reactions of H₂S on the surfaces.Addition of H₂S in the gasification gas stream has been found to improve naphthalene and ammonia conversion over ZrO₂ and Y₂O₃-ZrO₂ catalysts, whereas over SiO₂-ZrO₂ such effect has not been observed. The differences in the properties of the catalysts were studied by spectroscopic (MeOH-DRIFTS) and temperature-programmed methods (H₂S-TPD and MeOH-TPSR). Methanol was also used to probe the changes after sulfidation of the catalysts. H₂S adsorption sites were found to be different on the ZrO₂ and Y₂O₃-ZrO₂ catalysts compared with the ones on the SiO₂-ZrO₂ catalyst. Sulfur was also found to be more reactive on the ZrO₂ and Y₂O₃-ZrO₂ catalysts than on SiO₂-ZrO₂. It was suggested, that the positive effect of H₂S on naphthalene conversion during gasification gas clean-up is connected with the reactions of adsorbed sulfur on their surface. In contrast, on SiO₂-ZrO₂ the lack of such an effect may be related to limited reactivity of sulfur on the surface.

Keywords: Zirconia catalyst; Effect of H; ₂; S; MeOH adsorption; MeOH-DRIFTS

Iron-catalyzed nitrogen removal as N₂ from PAN-derived activated carbon by Yasuhiro Ohshima; Naoto Tsubouchi; Yasuo Ohtsuka (pp. 614-620).

Display Omitted► Fine particles of FeOOH are precipitated onto PAN-derived activated carbon as a model of coal char. ► The resulting sample is heated in an inert gas at 10°C/min up to 1000°C with a fixed bed quartz reactor. ► Nanoscale iron particles can promote N₂ formation from heterocyclic nitrogen at 600–1000°C. ► The in situ XRD analyses during heating show the formation of solid solution of Fe and N (and/or C). ► The iron-catalyzed N₂ formation may proceed through a mechanism involving the solid solution.Polyacrylonitrile-derived activated carbon as a model of coal char has been heated in high-purity He at 10°C/min up to 1000°C with a flow-type fixed bed quartz reactor, and the catalysis of N₂ formation by precipitated iron has been investigated by use of XPS, TEM and XRD methods. Fine iron particles with the average size of 15nm increase remarkably the formation rate between 600 and 1000°C, and N₂ yield up to 1000°C reaches about 65% at 1.9mass% Fe. The XPS and XRD measurements after heat treatment exhibit that nitrogen functionality does not change significantly, but carbon crystallization occurs through the dissolution of iron nanoparticles into the carbon substrate. The in situ XRD analyses during heating reveal the formation of austenite that is solid solution of Fe and N (and/or C). Interestingly, the catalysis of N₂ formation by iron and the formation of austenite occur at almost the same temperature range of 600–1000°C. It is thus likely that nanoscale iron particles move in the carbon matrix and react with heterocyclic nitrogen in order to produce the solid solution, which is subsequently decomposed into N₂.

Keywords: PAN-derived activated carbon; Heat treatment; Nitrogen removal; N; ₂; formation; Fe catalyst

Zn-containing ionic liquids bearing dialkylphosphate ligands for the coupling reactions of epoxides and CO₂ by Jin Kyu Lee; Young Jin Kim; Young-Seop Choi; Hyunjoo Lee; Je Seung Lee; Jongki Hong; Eun-Kyung Jeong; Hoon Sik Kim; Minserk Cheong (pp. 621-627).

Display Omitted► Synthesis of Zn-containing room temperature ionic liquids (Zn-RTILs). ► Zn-RTILs as highly active catalysts for the cycloaddition of CO₂ with epoxides. ► Mechanistic investigation on the roles of Zn-RTILs by computational calculations. ► Reduction of ethylene carbonate decomposition by a catalyst during the distillation.Zn-containing room temperature ionic liquids (Zn-RTILs), prepared from the reactions of ZnBr₂ with 1-alkyl-3-methylimidazolium dialkyphosphates ([RMIm][R₂PO₄]), were highly active for the coupling reactions of CO₂ with epoxides, producing corresponding cyclic carbonates in high yields. FAB-mass spectral and computational results suggest that [ZnBr(R₂PO₄)₂]⁻ could be an active species for the coupling reaction. Decomposition of cyclic carbonates into epoxides and CO₂ during the product recovery process via vacuum distillation was almost negligible even in the presence of a Zn-RTIL up to 130°C.

Keywords: Carbon dioxide utilization; Cyclic carbonates; Ionic liquids; Zinc bromide; Epoxides

The electrocatalytic dechlorination of chloroacetic acids at electrodeposited Pd/Fe-modified carbon paper electrode by Angzhen Li; Xu Zhao; Yining Hou; Huijuan Liu; Liyuan Wu; Jiuhui Qu (pp. 628-635).

. The dechlorination of chloroacetic acids at Pd/Fe-modified carbon paper electrode proceeded by direct and indirect reduction. Indirect reduction by atomic H* was the primary process to realize the complete dechlorination of chloroacetic acids by Pd/Fe-modified carbon paper cathode.Display Omitted► Electrodeposited Pd/Fe-C cathode exhibited high dechlorination ability. ► Stepwise dechlorination of TCAA and DCAA to MCAA was achieved by direct reduction. ► Chloroacetic acids were reduced to acetic acid via indirect reduction by H*. ► Pd(0) nanoparticles of Pd/Fe-C cathode played a significant role in forming H*. ► Fe(0) nanoparticles of Pd/Fe-C cathode could enhance the transport of electrons.Pd/Fe-modified carbon paper (Pd/Fe-C) electrode was prepared from PdCl₂ and FeSO₄ via electrodeposition onto carbon paper. It was observed that the diameters of electrodeposited Pd/Fe particles were around 20nm with a uniform distribution on carbon paper, which is smaller than Pd/Fe particles of impregnated and calcined electrode. The electrodeposited Pd/Fe-C electrode exhibited higher activity in dechlorination of chloroacetic acids than impregnated and calcined electrode. Under optimal experiment conditions of Pd:Fe molar ratio of 2:1 at −1.5V (vs SCE), 95% of trichloroacetic acid (TCAA) with the initial concentration of 500μg/L was removed within 20min at pH 3. The dechlorination of chloroacetic acids followed the order of TCAA>dichloroacetic acid (DCAA)>monochloroacetic acid (MCAA). MCAA cannot be dechlorinated at C and Fe-C electrodes via direct reduction. However, a part of chloroacetic acids was directly dechlorinated to acetic acid at Pd-C and Pd/Fe-C electrodes via indirect reduction. The Pd(0) and Pd(II) species were detected by X-ray photoelectron spectroscopy. Compared with the individual Pd-C electrode, in situ formation of Fe(0) decreased the interface impedance as observed by electrochemical impedance spectroscopy analysis. In conclusion, the presence of Pd(0) nanoparticles played a significant role in forming atomic H* to realize indirect reduction process which could achieve the complete dechlorination of chloroacetic acids.

Keywords: Pd/Fe-modified carbon paper electrode; Electrocatalytic dechlorination; Chloroacetic acids; Direct reduction; Indirect reduction

Reaction mechanism of visible-light responsive Cu(II)-grafted Mo-doped SrTiO₃ photocatalyst studied by means of ESR spectroscopy and chemiluminescence photometry by Yoshio Nosaka; Shinichiro Takahashi; Yasufumi Mitani; Xiaoqing Qiu; Masahiro Miyauchi (pp. 636-640).

The reaction mechanisms of visible-light responsive Cu(II)-grafted Mo-doped SrTiO₃ (Cu(II)/MoSTO) photocatalyst and related photocatalysts were analyzed by means of ESR spectroscopy for detecting trapped carriers at 77K and chemiluminescence photometry for O₂⁻ and H₂O₂ in aqueous suspension. On the irradiation of visible light, the reduction of grafted Cu²⁺ ions was observed by ESR measurements for both Cu(II)/MoSTO and Cu(II)/STO (Cu(II)-grafted undoped SrTiO₃) photocatalysts. One electron reduction product for O₂, i.e., O₂⁻, was detected in aqueous suspension by 442-nm irradiation for the Cu(II)-grafted samples. On the other hand, the amount of H₂O₂ detected as the two electron reduction product of O₂ was a very small scale, indicating possible further reduction of H₂O₂ into H₂O. From the ESR observations of crystalline defects, it was concluded that the Mo doping to increase visible-light response also increase the electron–hole recombination to some extent, while the Cu(II) grafting functioned as a trap of excited electrons to decrease the recombination.

Keywords: Visible light responsive photocatalyst; Mo doped SrTiO; ₃; Cu(II) graft; ESR; Superoxide radical

Strategies for enhanced CWPO of phenol solutions by N. Inchaurrondo; J. Cechini; J. Font; P. Haure (pp. 641-648).

A commercial CuO/alumina catalyst is used in the catalytic wet peroxide oxidation (CWPO) of 1g/l phenol solutions in a batch reactor. The effect of temperature, catalyst load, hydrogen peroxide concentration and dosage strategies on phenol mineralization, hydrogen peroxide consumption efficiencies and catalyst stability was studied.Simultaneous high mineralization and hydrogen peroxide consumption efficiencies are obtained with a proper oxidant dosage strategy. Total H₂O₂ added is close to the stoichiometric requirement. Phenol is completely abated with the first dose while subsequent peroxide additions complete the mineralization.(A) Phenol and TOC conversion vs. time. (B) H2O2 consumption and pH evolution vs. time.Display Omitted► Commercial CuO/alumina catalyst for CWPO of phenol solutions. ► Faster mineralization rates at higher temperatures, catalyst and H₂O₂ concentrations. ► Comparable results obtained with stoichiometric H₂O₂ dosage strategy.The performance of a commercial CuO/alumina catalyst used in the catalytic wet peroxide oxidation (CWPO) of 1g/l phenol solutions is investigated in a batch reactor. The effect of temperature, catalyst load, hydrogen peroxide concentration and dosage strategies on phenol mineralization, hydrogen peroxide consumption efficiencies and catalyst stability was studied. Experiments were performed at 298, 323 and 343K, using catalyst loads of 1g/l or 25g/l and concentrations of hydrogen peroxide 1.3, 2.6 and 3.9 times the stoichiometric requirement added at once or in distributed doses. The critical goal of the CWPO in terms of Process Intensification is to achieve total phenol mineralization working at optimal hydrogen peroxide consumption efficiencies while retaining catalyst stability. The present work highlights the complexity of this objective and shows viable working alternatives.Results indicate that high temperatures and concentrations of catalyst and hydrogen peroxide (added at once) can be employed when fast mineralization and high pH values are required in order to prevent catalyst leaching, although oxidant consumption efficiencies are then low. However, simultaneous high mineralization and hydrogen peroxide consumption efficiencies are obtained with a proper oxidant dosage strategy at high temperature, using high catalyst load. Then, hydrogen peroxide degradation into non-oxidising (parasitic) species is minimized with final TOC conversions close to 90%. The drawback of this strategy is that the rate of reaction is lower because of the limited amount of oxidant available.

Keywords: Phenol CWPO; H; ₂; O; ₂; addition; CuO catalyst

Commentary on the article: “A new kinetic model for heterogeneous photocatalysis with titanium dioxide: Case of non-specific adsorption considering back reaction, by S. Valencia, F. Cataño, L. Rios, G. Restrepo and J. Marín, published in Applied Catalysis B: Environmental, 104 (2011) 300–304” by J.F. Montoya; J. Peral; P. Salvador (pp. 649-650).

Keyword; TiO; ₂; photocatalysis

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Applied Catalysis B, Environmental (v.111-112, #)