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Applied Catalysis B, Environmental (v.103, #1-2)

Contents Continued (pp. i).

Editorial Board (pp. i).

IFC Editorial Board (pp. co2).

Contents (pp. co4).

Effect of the electronic state and copper localization in ZSM-5 pores on performance in NO selective catalytic reduction by propane by Oleg P. Krivoruchko; Tatyana V. Larina; Roman A. Shutilov; Vladimir Yu. Gavrilov; Svetlana A. Yashnik; Vladimir A. Sazonov; Irina Yu. Molina; Zinfer R. Ismagilov (pp. 1-10).

▪.► Cu( n)ZSM-5 prepared by incipient impregnation with CuCl₂ solution followed by hydrolytic polycondensation is active in NO SCR by propane. ► The fresh Cu( n)ZSM-5 contains (1) isolated Cu²⁺_Oh ions on ion-exchange zeolite sites; (2) isolated Cu²⁺_Oh ions on extraframework Al³⁺_Oh; (3) weakly bound linear Cu²⁺_Oh associates. The latter species transform to nanodispersed Cu₂(OH)₃Cl (4) during catalytic experiments. ► High catalytic activity in NO SCR by propane of Cu(0.5–1%)ZSM-5 is related to the isolated Cu²⁺_Oh ions on ion-exchange zeolite sites and on extraframework Al³⁺_Oh. ► Weakly bound linear Cu²⁺_Oh associates have lower activity. They are active in NO₂ SCR by propane, NO₂ being formed during NO disproportionation or oxidation on isolated Cu²⁺.This study was devoted to determination of localization of the individual copper species in the pores of ZSM-5 zeolite after post-synthetic zeolite modification by incipient wetness impregnation with CuCl₂ solution followed by hydrolytic polycondensation of the ions in the pores. A series of Cu( n)ZSM-5 samples, where n is the copper concentration varied from 0.5 to 5.0wt.%, were synthesized using this method. A commercial HZSM-5 zeolite having Si/Al=17 was used for the synthesis of the catalysts. After modification the Cu( n)ZSM-5 samples were dried and calcined in air at 110 and 450°C, respectively. The samples were studied by UV–vis–NIR DR spectroscopy, XRD and by measuring and processing the low-temperature (77K) adsorption of nitrogen and hydrogen. It was shown for the first time that at the concentration of 1.0wt.% or lower copper was localized in the form of isolated Cu²⁺_Oh cations in the ion-exchange positions in the zeolite micro- and mesopores as well as on oxygen complexes of extraframework aluminum in thin mesopores with D<3.2nm in the form of superficial spinel-like structures in octahedral oxygen coordination Cu²⁺_Oh. At the copper concentration above 1.0wt.% linear associates of weakly bound Cu²⁺_Oh ions with unusual orbital ordering were formed in addition to the two forms discussed above. These associates existing in the forms of one- and two-dimensional nanohydroxocompounds were localized partially in the zeolite micropores but mostly in thin mesopores.The effect of the individual copper species on the catalytic properties of Cu( n)ZSM-5 samples in selective catalytic reduction of NO by propane was also studied. It was found that isolated Cu²⁺_Oh cations in the ion-exchange positions and Cu²⁺_Oh cations localized on the oxygen complexes of extraframework aluminum had the highest catalytic activity in NO SCR by propane. The weakly bound linear associates of Cu²⁺_Oh ions had lower catalytic activity, compared with isolated Cu²⁺_Oh ions. When their amount was high, they caused steric hindrance for contact of the reagents with the more active sites. The Cu²⁺_Oh ion associates were found to transform to nanodispersed Cu₂(OH)₃Cl during catalytic experiments.

Keywords: Post-synthetic modification; HZSM-5; Modifying copper species; Localization; Extraframework aluminum; NO removal

Vapor phase catalytic degradation of bis(2-chloroethyl) ether on supported vanadia–titania catalyst by S. Chandra Shekar; Keshav Soni; Rajendra Bunkar; Manoj Sharma; Beer Singh; M.V.S. Suryanarayana; R. Vijayaraghavan (pp. 11-20).

The total oxidation activity of CEE increased with vanadia, which is attributed to the dehydrochlorination followed by cyclisation with acid sites to produce hydrofurans whereas the hydrolytic cleavage of –C–O bond over vanadia sites followed by extended oxidation to produce CO₂.Series of V₂O₅–TiO₂ catalysts with varying vanadium content are prepared by impregnation method. The catalyst composition is determined by XRD and Smart mapping (SEM–EDAX), respectively. The bulk reducibility of the catalyst is determined by the temperature programmed reduction (TPR). Catalyst activity and stability are elucidated in vapor phase catalytic degradation of bis(2-chloroethyl) ether (CEE). The factors affecting the process parameters such as gas hourly space velocity (GHSV), feed ratios, reaction temperature and vanadium content are studied for getting maximum degradation of CEE. Results reveal that vanadium content and reaction temperature have significant influence on the activity of catalyst, and the optimum vanadium content is identified for maximum degradation. The catalyst having monolayer coverage of vanadia (6% vanadium oxide) gave better performance for the degradation of CEE at 250°C and the total oxidation is predominant above 200°C. The GC–MS and ATD coupled GC–MS analyses reveal the degraded products are acetaldehyde, dihydrofurans, carbon dioxide, hydrochloric acid, trace amount of chloroacetaldehyde and chloroethanol, which confirms the proposed degradation path for total oxidation and partial oxidation. A 90% of CEE degradation is achieved at 300°C and GHSV of 19,000h⁻¹ over 6wt% of V₂O₅/TiO₂. A plausible surface mechanism is proposed based on the analyses results.

Keywords: CEE; TPR; Degradation mechanism; Vanadia–Titania

Solar photoelectro-Fenton degradation of paracetamol using a flow plant with a Pt/air-diffusion cell coupled with a compound parabolic collector: Process optimization by response surface methodology by Lucio Cesar Almeida; Sergi Garcia-Segura; Nerilso Bocchi; Enric Brillas (pp. 21-30).

Display Omitted▶ The coupling of a Pt/air cell with a solar compound parabolic collector photoreactor allows a quick degradation of paracetamol. ▶ Experimental variables like current, Fe²⁺ content and pH can be optimized by response surface methodology. ▶ Response surfaces for total organic carbon, energy cost and mineralization current efficiency describe the solar photoelectro-Fenton process.▶ The attack of hydroxyl radical on paracetamol gives aromatic products that are oxidized to carboxylic acids.▶ Carboxylic acids form Fe(III) complexes that are photolyzed by UV irradiation of sunlight.The degradation of 10L of 157mgL⁻¹ paracetamol solutions in 0.05M Na₂SO₄ has been studied by the solar photoelectro-Fenton (SPEF) method. A solar flow plant with a Pt/air-diffusion electrochemical cell and a compound parabolic collector (CPC) photoreactor was used operating under recirculation mode at a liquid flow of 180Lh⁻¹ with an average UV irradiation intensity of about 32Wm⁻². A central composite rotatable design coupled with response surface methodology was applied to optimize the experimental variables. Optimum SPEF treatment was achieved by applying a current of 5A, 0.40mM Fe²⁺ and pH 3.0 at 120min of electrolysis, being reduced total organic carbon (TOC) by 75%, with an energy cost of 93kWhkg⁻¹ TOC (7.0kWhm⁻³) and a mineralization current efficiency of 71%. Initial N was partially converted into NH₄⁺ ion. Under these optimized conditions, paracetamol decays followed a pseudo first-order kinetics. HPLC analysis of the electrolyzed solution allowed the detection of hydroquinone, p-benzoquinone, 1,2,4-trihydroxybenzene, 2,5-dihydroxy- p-benzoquinone and tetrahydroxy- p-benzoquinone. All aromatics were destroyed by the attack ofOH. Maleic, fumaric, succinic, lactic, oxalic, formic and oxamic acids were identified as generated carboxylic acids, which form Fe(III) complexes that are quickly photodecarboxylated under UV irradiation of sunlight. A reaction sequence involving all the detected byproducts was proposed for the SPEF degradation of paracetamol.

Keywords: Paracetamol; Solar photoelectro-Fenton; Central composite rotatable design; Response surface methodology; Oxidation products

Pulsed Laser Deposition of Co-nanoparticles embedded on B-thin film: A very efficient catalyst produced in a single-step process by Nainesh Patel; Antonio Miotello; Valentina Bello (pp. 31-38).

Display Omitted▶ Spherical Co NPs partially embedded within B matrix are produced in a single-step deposition. ▶ This novel catalyst film used for hydrolysis of chemical hydrides. ▶ The catalytic activity is similar to Pt/C and significantly better than that with Pd/C catalyst powder.Advances in “ Nanotechnology” may open the way to replace expensive traditional noble-metal with cheaper new catalyst entries without losing efficiency. Here we show that Pulsed Laser Deposition of Co-nanoparticles partially embedded into B-thin film catalyst is a step towards this direction. Depending on the energy density, the laser process is able to produce well-dispersed spherical Co nanoparticles, with average size of 11–15nm, partially embedded within B-based film matrix in a single-step deposition. This novel catalyst film exhibits catalytic activity comparable to that observed with commercial Pt/carbon black catalyst and significantly better than that with Pd/carbon black powder for hydrogen production by hydrolysis of chemical hydrides. Availability of a large number of under-coordinated active atoms owing to the size and shape of Co nanoparticles, polycrystalline nature of nanoparticles with linear defects in form of grain boundaries, and optimum interaction with reactant provided by electron enrichment from B, are the main features acquired by the Co nanoparticles that exhibit high catalytic efficiency. Boron plays a crucial role in avoiding coarsening of Co nanoparticles during both the reaction course and the heat treatment while offering, at same time, high tolerance against deactivation and oxidation by electron transfer to Co.

Keywords: Co nanoparticles; H; ₂; production; Pulsed Laser Deposition; Thin film catalyst

H₂ oxidation and preferential CO oxidation over Au: New approaches by Mikhail Kipnis; Elvira Volnina (pp. 39-47).

.Display Omitted▶ H₂ oxidation and CO-PROX (∼1% O₂) can be performed in the mode of Au-catalyst surface ignition. ▶ Transfer into catalyst surface ignition starts at the exit from the catalyst bed with height ∼1.5cm. ▶ Key factors of CO-PROX: exothermic oxidation reactions CO and H₂, the character of interaction between Au and oxygen of reaction media. ▶ Self-activation of Au-catalysts is discovered for H₂-rich gases with or without CO.H₂ oxidation and preferential CO oxidation (CO-PROX) were studied over Au/Al₂O₃-catalysts with gold content 0.2–1wt.% in a flow reactor of quartz.It is established that the reactions of H₂ oxidation and CO-PROX can be performed in a mode of the catalyst surface ignition (CSI). If temperature/gas flow rate are varied within certain limits, this mode can be maintained. Oxygen is the key component in CSI mode in the case of H₂-rich gases; its residual content is below 70ppm. Residual content of CO in CSI mode depends on temperature, gradually decreasing upon a decrease in temperature in the “hot spot” of the reaction zone.In oxidation reactions conducted in CSI mode, the “hot spot” of the reaction zone is situated at the exit from the catalyst bed in two cases: when the catalysts are of low Au content, or when the temperature is lowered. This is a sign of catalyst deactivation at the entrance to the catalyst bed.Self-activation of the catalyst is found in both presence and absence of CO as a spontaneous overheat of the catalyst over time with “hot spot” drifting from the exit of the catalyst bed to the entrance.It is proposed that both deactivation and self-activation are caused by rival processes on the surface of gold: strong binding of oxygen and oxygen removal by desorption or consumption in exothermic oxidation processes. Thus, the positive effect of hydrogen on CO oxidation can be connected both with a change in ratio between different valent forms of gold and the conjugation of oxidation reactions.

Keywords: CO preferential oxidation; H; ₂; oxidation; Surface ignition; Gold

A photophysical approach to investigate the photooxidation mechanism of pesticides: Hydroxyl radical versus electron transfer by M.L. Marin; V. Lhiaubet-Vallet; L. Santos-Juanes; J. Soler; J. Gomis; A. Arques; A.M. Amat; M.A. Miranda (pp. 48-53).

Display Omitted► The role of OH has been investigated by laser flash photolysis. ► The reaction rate constants of five pesticides with OH have been determined. ► Results under photo-Fenton conditions are in agreement with OH involvement. ► The oxidation pattern using TiO₂ suggests a mixed mechanism. ► Using TPP, photoinduced electron transfer occurs within a ground state complex.The role of hydroxyl radical in different solar photocatalytic processes, namely photo-Fenton, titanium dioxide-based oxidation and organic photocatalysis (triphenylpyrylium) has been investigated. Using a methodology based on the flash photolytic generation of OH from N-hydroxypyridine-2(1H)-thione, followed by t-stilbene trapping, the reaction rate constants of different pesticides (dimethoate, methidathion, alachlor and pyrimethanyl) with this reactive oxygen species in deaerated acetonitrile have been determined. The results obtained under photo-Fenton conditions are in reasonable agreement with the estimated rate constants; hence the assumption that the photo-Fenton reaction mainly involves participation of the hydroxyl radical seems plausible. The oxidation pattern using titanium dioxide was also investigated; however, under these conditions no clear correlation could be found due to participation of an alternative electron transfer mechanism.Finally, pyrimethanil was the most reactive pesticide when photodegradation was carried out in the presence of TPP, in spite of its low reactivity towards hydroxyl radical. Laser flash photolysis experiments evidenced that the reaction occurs via photoinduced electron transfer within a ground state complex; this is in good correlation with the relative amount of pyranyl radical formation.

Keywords: Hydroxyl radical; Laser flash photolysis; Photo-Fenton; Titanium dioxide; Triphenylpyrylium

Low-temperature oxidation of ethanol over a Mn_0.6Ce_0.4O₂ mixed oxide by Huaju Li; Gongshin Qi; Tana; Xiaojing Zhang; Xiumin Huang; Wei Li; Wenjie Shen (pp. 54-61).

Display Omitted▶ A Mn_0.6Ce_0.4O₂ mixed oxide is highly active and stable for ethanol oxidation. ▶ Ethanol is totally converted to CO₂ at 463K and maintains for 120h on-stream. ▶ Solid solution enables effective activation of molecular oxygen in the feed gases. ▶ Migration of active oxygen species on the catalyst surface is of utmost importance.A Mn_0.6Ce_0.4O₂ mixed oxide exhibited rather high activity and stability for ethanol oxidation. Complete conversion of ethanol to CO₂ was obtained at a temperature as low as 463K and the activity maintained for 120h on-stream without obvious deactivation. The Mn_0.6Ce_0.4O₂ catalyst showed higher ethanol oxidation rate and better selectivity to CO₂ which was even superior to a Pt/Al₂O₃ catalyst. Temperature-programmed surface reaction and spectroscopic studies have revealed that ethoxy species were formed immediately upon ethanol adsorption on the catalyst at room temperature. These intermediates were further oxidized to acetate and carbonate species, and finally converted to CO₂ at elevated temperatures. The effective activation of molecule oxygen over the Mn_0.6Ce_0.4O₂ solid solution plays an essential role in determining the catalytic performance. Oxygen transfer from molecular oxygen to MnO₂ active sites through CeO₂ in the solid solution realized the effective activation of molecular oxygen. At lower temperatures, the oxidation of ethanol mainly produced acetaldehyde, and the direct oxidation of ethanol to CO₂ became the major route at higher temperatures, depending on the activation of molecular oxygen.

Keywords: Mn; _0.6; Ce; _0.4; O; ₂; mixed oxide; Solid solution; Ethanol oxidation; Molecular oxygen; Activation

Catalytic decomposition of N₂O over highly active supported Ru nanoparticles (≤3nm) prepared by chemical reduction with ethylene glycol by Vasilis G. Komvokis; Maria Marti; Andreas Delimitis; Iacovos A. Vasalos; Kostas S. Triantafyllidis (pp. 62-71).

Display Omitted▶ Catalysts with highly dispersed Ru nanoparticles (1–3nm) by ethylene glycol reduction. ▶ Decomposition of N₂O over nano-Ru/γ-Al₂O₃ is a structure–sensitive reaction. ▶ Nano-Ru/γ-Al₂O₃ is highly active for N₂O decomposition (combustion off-gases). ▶ Nano-Ru/γ-Al₂O₃ is deactivated by water and NO (reversibly) and SO₂ (irreversibly). ▶ Nano-Ru/γ-Al₂O₃ can be regenerated under thermal treatment with hydrogen.In the present work we studied the N₂O decomposition activity of nano-Ru/γ-Al₂O₃ catalysts prepared by in situ reduction with ethylene glycol (EG), in comparison to catalysts prepared via typical incipient wetness procedure. The metal content, particle size, dispersion and reduction characteristics of the supported Ru catalysts were studied by means of ICP-AES, XRD, HRTEM, TPR-H₂ and TPD-H₂. The EG reduction method favored the formation of almost spherical metallic Ru nanoparticles with the size of 1–3nm (HRTEM) and dispersion of 70–35% (TPD-H₂), at Ru loading levels of 0.4–1wt.%. The impregnated-calcined catalysts exhibited larger Ru nanoparticles (10–80nm, TEM) with very low degree of dispersion (∼10%). The activity of the EG-prepared catalysts for the decomposition of N₂O in oxygen rich feeds and in the absence or presence of NO, H₂O, SO₂, CO and CO₂, was significantly higher compared to that of the impregnated-calcined samples and comparable with that of the most active catalytic systems reported in the literature for the treatment of combustion processes off-gases. The superior activity of the former catalysts, especially of the sample with low Ru content (0.4wt.% Ru, 1–2nm particle size), was attributed both to the high dispersion of Ru (70% dispersion), i.e., the high surface area of Ru metal available for reaction, and to the higher intrinsic activity and lower apparent activation energy of the very small supported Ru nanoparticles prepared by the EG reduction method. The EG-prepared nano-Ru/γ-Al₂O₃ catalysts could retain their high N₂O decomposition activity (higher than 90%) for long time-on-stream by applying intermediate, short term regenerations in reducing atmosphere at moderate temperatures (i.e., 500°C); treatment of the partially deactivated catalysts under reducing (H₂/He) atmosphere leads to elimination of Ru(SO₄)₂ that is usually formed during reaction via reduction of Ru⁴⁺ to active Ru metallic phase.

Keywords: Nitrous oxide – N; ₂; O; Decomposition; Ethylene glycol; Ruthenium nanoparticles; Supported catalysts; Regeneration

Formaldehyde production from methanol and methyl mercaptan over titania and vanadia based catalysts by Niina Koivikko; Tiina Laitinen; Satu Ojala; Satu Pitkäaho; Alexei Kucherov; Riitta L. Keiski (pp. 72-78).

Display Omitted► VOC emissions can be utilized to produce useful chemicals. ► Methanol and methyl mercaptan can be simultaneously converted to formaldehyde. ► Highest conversions and selectivities were gained with V₂O₅/SiO₂+TiO₂ catalyst. ► Temperature over 300°C is required for high formaldehyde production. ► No signs of catalyst deactivation due to sulphur was observed.The results of selective oxidation of CH₃OH and CH₃SH to produce formaldehyde are presented and the effect of the reaction conditions on the CH₂O yield is evaluated. The yield of formaldehyde was evaluated by thermodynamic calculations by using the HSC Chemistry^® and Aspen Plus^® simulation programmes. Oxidation of CH₃OH and CH₃SH was investigated by calculating the system equilibrium composition. Based on the modelling results, the yield of formaldehyde was almost zero with all the reactants present, i.e. the CH₃OH, CH₃SH and CH₃OH+CH₃SH mixture, which was also supported by the experiments. Catalytic experiments were performed over TiO₂, V₂O₅/SiO₂ and V₂O₅/(SiO₂+10% TiO₂) catalysts to evaluate the effect of feed concentration, reaction temperature and catalyst loading on the formaldehyde yield. Both CH₃OH and CH₃SH were oxidized separately and as mixtures. The V₂O₅/(SiO₂+10% TiO₂) catalyst was the most active catalyst in formaldehyde production. At optimal reaction conditions, 88% yield of CH₂O was achieved at 413°C in a feed mixture of 1000ppm of CH₃OH+CH₃SH with the space velocity of 94,000h⁻¹. The catalysts showed no activity loss when tested for 6h.

Keywords: Catalytic oxidation; Vanadium pentoxide; Methanol; Methyl mercaptan; Environmental catalysis

A Niobia-Ceria based multi-purpose catalyst for selective catalytic reduction of NO_x, urea hydrolysis and soot oxidation in diesel exhaust by Maria Casapu; Andreas Bernhard; Daniel Peitz; Max Mehring; Martin Elsener; Oliver Kröcher (pp. 79-84).

Display Omitted► A new niobia-ceria based catalyst for the SCR of NO_x with NH₃ is reported. ► The catalyst exhibits a similar catalytic activity compared to the conventional vanadia-based SCR catalysts. ► The niobia-ceria catalyst may simultaneously act as an excellent urea hydrolysis and a good soot oxidation catalyst.We report about a novel niobia-ceria based catalyst that may be applied for the selective catalytic reduction (SCR) of NO_x as well as the catalytic regeneration of diesel particulate filters (DPF) in diesel engines. The material proved to be active in model gas experiments for a series of important reactions in these processes: (1) the SCR of NO with NH₃, (2) the hydrolysis of urea to NH₃ and (3) the oxidation of soot. The catalyst was able to convert 72% NO already at 250°C and showed almost full NO reduction between 300 and 450°C. The new niobia-ceria exhibited a similar urea hydrolysis activity as compared to a conventional TiO₂ catalyst. A significant decrease of the soot oxidation temperature was also noticed with this catalyst.

Keywords: Selective catalytic reduction; Urea hydrolysis; Soot oxidation; Cerium oxide; Niobium oxide

Photodegradation kinetics of stearic acid on UV-irradiated titania thin film separately followed by optical microscopy and Fourier transform infrared spectroscopy by M.N. Ghazzal; N. Barthen; N. Chaoui (pp. 85-90).

Display Omitted► Stearic acid (SA) deposited on TiO2 film forms islands of variable sizes and heights. ► Upon UV light, overall SA decomposes according to a pseudo first-order kinetics. ► However, the decomposition of an individual SA island is of the zero-order type. ► Collective effect of islands disappearance explains the pseudo first-order kinetics.We use optical microscopy for observing the photocatalytical decomposition of SA on titania film during exposure to a simulated solar illumination. The titania films were prepared via sol–gel and deposited on a borosilicate glass substrate by dip-coating. A low amount of SA was deposited by dipping the titania film in a methanolic SA solution. Optical micrographs showed that the deposited SA forms islands with variable heights and sizes and that upon UV-irradiation, these latter decomposed gradually from the edges towards the center. The SA photodecomposition as evaluated by measuring the integrated IR absorbance of SA in the 2700–3000cm⁻¹ region, proceeded according to a pseudo first-order kinetics with respect to SA. By contrast, it was of the zero-order type when monitoring the decomposition of an individual SA island by microscopy. From these results, we showed that the pseudo first-order kinetics is the result of a collective effect of many independent and parallel zero-order reactions with variable durations. This scenario describes well both the experimental data and those reported in literature.

Keywords: Titanium oxide; Thin film; Photocatalysis; Self-cleaning surface; Stearic acid

Calcined zirconium sulfate supported on MCM-41 silica as acid catalyst for ethanolysis of sunflower oil by I. Jiménez-Morales; J. Santamaría-González; P. Maireles-Torres; A. Jiménez-López (pp. 91-98).

Display Omitted▶ Calcination of zirconium sulfate supported on MCM-41 silica leads to stable sulfated zirconia. ▶ The resulting catalysts are active in the ethanolysis of sunflower oil. ▶ Their activity is maintained after three catalytic cycles. ▶ These acid catalysts simultaneously catalyze the esterification of fatty acids and the transesterification of triglycerides.Stable sulfated zirconia can be prepared by impregnation with zirconium sulfate on a mesoporous silica type MCM and ulterior calcination at 750°C. The thermal decomposition of this salt leads to the formation of monoclinic/tetragonal zirconia with some sulfate ions strongly retained, which are acidic and enable to produce the ethanolysis of sunflower oil at 200°C. With only 14.6wt% of catalyst containing 30% of zirconium sulfate, 91.5wt% of biodiesel formation is attained. The catalysts are stable and no leaching of sulfate species to the reaction medium is found. Moreover, these catalysts give rise to the simultaneous esterification of FFAs and the transesterification of triglycerides even with 9% of FFAs. The activity of this catalyst is still maintained in the presence of 5wt% of water and after three catalytic cycles without any treatment.

Keywords: Zirconium sulfate; Transesterification; Sunflower oil; Mesoporous silica; Sulfated zirconia; Ethanolysis

Visible light photocatalytic activities of S-doped TiO₂-Fe³⁺ in aqueous and gas phase by Víctor M. Menéndez-Flores; Detlef W. Bahnemann; Teruhisa Ohno (pp. 99-108).

Display Omitted► Visible light photocatalytic activity of S-doped TiO₂-Fe³⁺. ► Decomposition of toxic and recalcitrant pollutants in aqueous and gas phase. ► The photocatalyst present high stability to be reused without further treatments.The photocatalytic activity of a sulfur-doped titanium dioxide material with adsorbed ferric oxide was analyzed for the degradation of different model compounds. Dichloroacetic acid (DCA) was decomposed in the aqueous phase and NO_x was decomposed in the gas phase. The stability of the photocatalyst was examined as a function of the recycling times by degradation of DCA at pH 3. The photocatalyst showed quite high photoactivity under visible light illumination. The best performance for decomposing DCA was obtained at pH 3. Results of inductively coupled sequential plasma (ICPS) analysis indicated that this photocatalyst is stable and appropriate for long-term commercial applications.

Keywords: Photocatalysis; S-doped TiO; ₂; -Fe; ³⁺; Visible light activity

Influence of the characteristics of carbon materials on their behaviour as heterogeneous Fenton catalysts for the elimination of the azo dye Orange II from aqueous solutions by Filipa Duarte; F.J. Maldonado-Hódar; Luis M. Madeira (pp. 109-115).

Display Omitted► Azo-dye Orange II is degraded by a complex heterogeneous Fenton process, where adsorption and oxidation co-exist. ► Three commercial activated carbons (Norit RX 3 Extra, Merck and Kynol) were studied as Fenton catalysts (impregnated with 7wt.% of iron). ► Activated carbons’ performance depends on their textural properties, and in this case, mainly on the size of the micropores and metal dispersion. ► Norit activated carbon showed to have the more appropriate textural properties for the removal of OII from aqueous solution, either by adsorption or by a catalytic Fenton-like process.This work deals with the elimination of the azo-dye Orange II (OII) by the heterogeneous Fenton's process. Three different commercial activated carbons (ACs), Norit RX 3 Extra, Merck and Kynol, were used as Fe-supports to develop Fenton catalysts (7wt.% Fe/C). Both supports and catalysts were characterized by several techniques (N₂ and CO₂ adsorption, XRD, TEM). The elimination of the dye is a complex heterogeneous process with co-existence of adsorption and oxidation. Adsorption and catalytic experiments were carried out with only 0.1gL⁻¹ of solid in a slurry batch reactor at 30°C, pH 3 and initial dye concentration of 0.1mM. The decolorization was followed continuously by the absorbance measurement; mineralization and leaching levels were evaluated by TOC and atomic absorption analyses, respectively. Correlations of ACs characteristics with their adsorptive or catalytic performances were established, in order to select the best support. All the ACs are microporous materials and the OII adsorption is favoured by an increase of the micropore width. Although the carbon surface proves to be catalytically active, the main OII elimination process in pure ACs is adsorption, while for the Fe-catalyst it is determined by the Fenton oxidation. The Fe-Norit is the most active catalyst, which is associated to its high surface area located on large micropores that favours both the OII adsorption and the Fe-dispersion. However, this catalyst presented the highest tendency to the leaching. Anyway, the leaching values remain quite low even in this case (<1.7% of the total Fe), guarantying the possible reuse of the catalysts.

Keywords: Orange II; Heterogeneous Fenton; Activated carbons; Leaching; Norit RX 3 Extra

Displacement reaction of Pt on carbon-supported Ru nanoparticles in hexachloroplatinic acids by Yu-Chi Hsieh; Li-Chung Chang; Pu-Wei Wu; Yun-Min Chang; Jyh-Fu Lee (pp. 116-127).

Display Omitted▶ Displacement reaction of Pt on Ru nanoparticles to form PtRu nanoparticles. ▶ Adjusting the pH value of hexachloroplatinic acids affects the extent of displacement reaction. ▶ X-ray absorption spectroscopy provides structural determination on PtRu formation. ▶ CO stripping and H₂ oxidation confirm desirable PtRu structure.The displacement reaction of Pt on Ru to form a Ru core and Pt shell (Ru@Pt) bimetallic structure is investigated by immersing the carbon-supported Ru nanoparticles in hexachloroplatinic acids with pH of 1, 2.2, and 8, followed by a hydrogen reduction treatment. Results from inductively coupled plasma mass spectrometry suggest that the dissolution of Ru is mostly caused by the reduction of Pt cations. Images from transmission electron microscopy demonstrate a uniform distribution of Ru@Pt in size of 3–5nm. Spectra from X-ray absorption near edge structure and extended X-ray absorption fine structure confirm that the pH value of hexachloroplatinic acid determines the type of ligands complexing the Pt cations that affects their activity and consequently the severity of displacement reaction and alloying degree of Ru@Pt nanoparticles. As a result, the samples from pH 1 bath reveal a desirable core–shell structure that displays a reduced onset potential in CO stripping and stable catalytic performance for H₂ oxidation while the samples from pH 8 bath indicate the formation of Pt clusters on the Ru surface that leads to poor CO stripping and H₂ oxidation characteristics.

Keywords: Displacement reaction; PtRu bimetallic nanoparticles; Hexachloroplatinic acid; Methanol oxidation; X-ray absorption spectroscopy

Compared activity and stability of Pd/Al₂O₃ and Pd/AC catalysts in 4-chlorophenol hydrodechlorination in different pH media by Zahara M. de Pedro; Elena Diaz; Angel F. Mohedano; Jose A. Casas; Juan J. Rodriguez (pp. 128-135).

Display Omitted► The highest reaction rate with Pd/Al₂O₃ catalyst took place at pH ≈8.5. ► Pd/Al₂O₃ suffered a similar loss of activity in plain water and NaOH solution. ► Deactivation of Pd/Al₂O₃ was associated with the formation of Pd–Cl complexes. ► A higher activity and stability was exhibited by Pd/AC catalyst.Hydrodechlorination of 4-chlorophenol using Pd/A₂O₃ as catalyst at mild conditions (30°C, 1atm) was carried out in plain water, buffered (CH₃COOH/NaCH₃COO, NaH₂PO₄/Na₂HPO₄ and NaHCO₃/Na₂CO₃) and alkaline NaOH media at different pH. The highest reaction rate was achieved when the process was carried out at alkaline NaOH solution of pH=8.5. Continuous long term experiments ( τ: 5.4kg_cath/mol) were performed in plain water and alkaline medium using Pd/Al₂O₃ and Pd/AC as catalysts. The former showed an appreciable loss of activity upon time on stream, which was associated with the formation of palladium chloride complexes. However, a residual activity remained practically stable, reaching very similar 4-chlorophenol conversion (36%) in both reaction media. The Pd/AC catalyst maintained a constant activity at a 70% 4-chlorophenol conversion once the steady state was reached. This suggests that the AC supported catalyst is less susceptible to the chloride poisoning produced during the reaction.

Keywords: Catalytic hydrodechlorination; 4-Chlorophenol; Pd/Al; ₂; O; ₃; Pd/AC; pH

Nanocomposites of poly(1-naphthylamine)/SiO₂ and poly(1-naphthylamine)/TiO₂: Comparative photocatalytic activity evaluation towards methylene blue dye by Sadia Ameen; M. Shaheer Akhtar; Young Soon Kim; Hyung Shik Shin (pp. 136-142).

Display Omitted► The effective PNA/SiO₂ and PNA/TiO₂ nanocomposites exhibit a potential viability to degrade the MB dye by ∼28% and ∼60% respectively under visible light illumination. ► Remarkable photocatalytic activity of PNA/TiO₂ nanocomposite attributes to the efficient high charge separation of ē–h⁺ pairs in the excited states of coupled PNA and TiO₂ nanomaterials. ► The SiO₂ and TiO₂ are low-price, eco-friendly oxides with high chemical and thermal stability, and have abilities to deliver the effective photocatalytic activities towards organic pollutants.The in situ polymerization of 1-naphthylamine monomer with silica (SiO₂) and titania (TiO₂) was adopted for the preparation of distinct poly 1-naphthylamine (PNA)/SiO₂ and PNA/TiO₂ nanocomposites. The absorption spectra of the nanocomposites showed a considerable red shift compared to pristine PNA which indicated the decrease in the orbital overlap between the π-electrons of the naphthyl rings with the lone pair of the nitrogen atom in the PNA molecules. The structural and the surface characterizations presented an effective interaction through the hydrogen bonding between imine (–NH) of PNA and hydroxyl (–OH) group of nanomaterials (SiO₂/TiO₂). The prepared nanocomposites showed a significant photocatalytic activity for the degradation of methylene blue (MB) dye under visible light illumination. It was found that MB dye degraded more efficiently by ∼60% over the surface of PNA/TiO₂ nanocomposites than PNA/SiO₂ (∼28%) and pristine PNA (9%) might due to the existence of high photogenerated ē–h⁺ pairs charge separation.

Keywords: Poly 1-naphthylamine; Nanocomposite; XPS analysis; Photocatalytic activity

Catalytic oxidation of benzene over CuO/Ce1−_xMn_xO₂ catalysts by Ting-Yi Li; Shu-Jen Chiang; Biing-Jye Liaw; Yin-Zu Chen (pp. 143-148).

Display Omitted► Incorporating manganese into CeO₂ to form Ce1−_xMn_xO₂ solution increased the mobility of lattice oxygen and considerably improved the performance of Ce1−_xMn_xO₂ and even the catalysts of CuO/Ce1−_xMn_xO₂ in the oxidation of benzene. ► The oxidation of benzene over CuO/Ce1−_xMn_xO₂ proceeded along three paths: (a) benzene that had been adsorbed on Ce_0.7Mn_0.3O₂ was oxidized by the release of oxygen from Ce_0.7Mn_0.3O₂, (b) benzene adsorbed on CuO was oxidized by oxygen that was released from CuO, or (c) benzene adsorbed on CuO was oxidized by oxygen that was released from Ce_0.7Mn_0.3O₂. ► The redox interaction between CuO and Ce_0.7Mn_0.3O₂ facilitated the activation of surface oxygen for reaction. The defective oxygen sites on the dispersed MnO_x enhanced the adsorption and oxidation of benzene.Ce1−_xMn_xO₂ ( x=0.1–0.6) mixed oxides were used as supports for preparing 7%CuO/Ce1−_xMn_xO₂ catalysts by impregnation, for use in the total oxidation of benzene. At x=0.1 and 0.2, most of manganese was fixed in the fluorite structure of CeO₂ to form a solid solution. When x exceeds 0.3, some of the manganese appeared as well dispersed MnO_x. The redox interaction between CuO and Ce_0.7Mn_0.3O₂ facilitated the activation of surface oxygen for the oxidation of benzene. The defective sites of oxygen on the dispersed MnO_x also enhanced the adsorption and oxidation of benzene. 7%CuO/Ce_0.7Mn_0.3O₂ catalyst was a good candidate for replacing noble metal catalysts for the removal of benzene in low concentrations at low temperature.

Keywords: Benzene; CuO catalyst; CeO; ₂; oxide; Ce–Mn–O mixed oxides; Oxidation

NO reduction property of apatite-type La₈A₂Si₆O₂₆ (A=Ca, Sr, Ba) supported Pt catalyst by Atsunori Ono; Mitsuaki Abe; Sumio Kato; Masataka Ogasawara; Takashi Wakabayashi; Yuunosuke Nakahara; Shinichi Nakata (pp. 149-153).

Display Omitted▶ The composition of support affected the reduction property of Pt on the catalyst. ▶ The oxidized Pt species on fresh catalysts were reduced during C₃H₆–NO–O₂ reaction. ▶ The composition of apatites affected catalytic activity for reactions involving C₃H₆.Apatite-type silicate (La₈A₂Si₆O₂₆ (A=Ca, Sr, Ba)) supported Pt catalysts were prepared and their catalytic activities were investigated for NO reduction. La₈A₂Si₆O₂₆ were obtained by the sol–gel method. Pt/La₈A₂Si₆O₂₆ (A=Ca, Sr, Ba) catalysts loaded with 1mass% of Pt were prepared by the impregnation method. The maximum NO conversions for C₃H₆–NO–O₂ reaction over Pt/La₈A₂Si₆O₂₆ catalyst were 37%, 41% and 50% for A=Ca, Sr and Ba, respectively. The reduction properties of Pt on the catalysts were evaluated by temperature programmed reduction (TPR). The composition of the apatite-type support affected the reduction property of Pt on the catalyst, resulting in promotion of catalytic activity for C₃H₆–NO–O₂ reaction below 300°C.

Keywords: Apatite-type silicate; NO reduction; Pt catalyst

Influence of Ba precursor on structural and catalytic properties of Pt–Ba/alumina NO_x storage-reduction catalyst by Nobutaka Maeda; Atsushi Urakawa; Renu Sharma; Alfons Baiker (pp. 154-162).

Display Omitted► Influence of Ba precursor on the structure and stability of Ba components. ► Influence of Ba precursor on the state of Pt. ► Crystallite size changes induced by NSR cycles. ► Influence of Ba crystallite size and the state of Pt on the NSR mechanisms. ► Morphological changes (melting) of Ba species by H₂O vapor.The effect of the choice of barium precursor (nitrate or acetate), in the preparation of Pt–Ba/γ-Al₂O₃ NSR catalysts, on their structure and catalytic behavior has been investigated by means of X-ray diffraction (XRD), temperature-programmed desorption (TPD), temperature-programmed reduction (TPR), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and catalytic tests. XRD patterns showed that the type of Ba precursor and repeated NSR cycles influence the crystallinity of Ba species. Depending on the Ba precursor, remarkable differences in Ba(NO₃)₂ crystallite sizes as well as availability of the Pt for hydrogen chemisorption were observed. TPD and TPR studies showed that the catalyst prepared using the Ba acetate-precursor route is more efficient in the decomposition and reduction of Ba nitrates at lower temperatures. The catalyst prepared by the Ba acetate-precursor route showed both enhanced NO_x storage ability and selectivity toward nitrogen in the reduction process, which is attributed to the intimate contact of the small crystallites of the Ba-component and the Pt particles. Environmental transmission electron microscopy (ETEM) measurements revealed that introduction of H₂O vapor induces morphological changes of the Ba phase leading to partial liquefaction as a result of the formation of hygroscopic barium hydroxides. The interplay of this liquid-like behavior of the Ba phase together with the chemical transformations occurring during NO_x storage and reduction can lead to remarkable structural changes affecting the NSR performance.

Keywords: NO; _x; storage-reduction; Ba storage component; Barium acetate; Barium nitrate; Pt–Ba/alumina; Crystallite size; Influence of H; ₂; O; ETEM

A highly active carbon-supported PdSn catalyst for formic acid electrooxidation by DandanTu; Bing Wu; Bingxing Wang; Chao Deng; Ying Gao (pp. 163-168).

Display Omitted► High active and stable PdSn/C catalyst for formic acid electrooxidation. ► High dispersed PdSn/C catalyst for formic acid electrooxidation. ► Kinetic parameters were obtained for formic acid electrooxidation at PdSn/C catalyst. ► The activation energy at different potential for formic acid oxidation was obtained.A carbon-supported PdSn (PdSn/C) catalyst was prepared by a chemical reduction method with the aid of microwave radiation and was characterized by X-ray diffraction spectroscopy and energy dispersive spectroscopy. Formic acid electrooxidations on PdSn/C and Pd/C catalysts were investigated and compared in an acidic medium by voltammetry and chronoamperometry. The results show that the performance of the PdSn/C-3 catalyst which ratio of Pd:Sn is about 3:1 for formic acid oxidation is greatly improved compared with that of Pd/C; thus, PdSn/C-3 is a promising candidate as an anode catalyst in direct formic acid fuel cells. Additionally, the value of the apparent activation energy shows that the activity of formic acid oxidation on the PdSn/C is sensitive to the temperature at relatively high potentials.

Keywords: Formic acid; Tin; Palladium; Electrocatalysis

Catalytic performance on iron-based Fischer–Tropsch catalyst in fixed-bed and bubbling fluidized-bed reactor by Suk-Hwan Kang; Jong Wook Bae; Joo-Young Cheon; Yun-Jo Lee; Kyoung-Su Ha; Ki-Won Jun; Dong-Hyun Lee; Byung-Woo Kim (pp. 169-180).

Display Omitted► Fischer–Tropsch synthesis (FTS) was investigated in fixed-bed reactor (FBR) and bubbling fluidized-bed reactor (BFBR). ► Co-production of C₂–C₄ olefins and clean fuels is maximized in BFBR. ► High CH₄ and CO₂ selectivities were induced from the inhibition of iron carbide formation. ► K/FeO_x catalysts can be a good candidate for applying in BFBR.Fischer–Tropsch synthesis (FTS) for the co-production of C₂–C₄ olefins and clean fuels such as gasoline and middle distillate from syngas was investigated on four different iron-based catalysts in a fixed-bed and a bubbling fluidized-bed reactor. The catalysts were prepared by wet-impregnation using the Al₂O₃, SiO₂ and iron ore (FeO_x) supports with the active components of Fe, K and (or) Cu, and each K/FeCuAlO_x catalyst was prepared by a co-precipitation method. Except for the catalyst impregnated on SiO₂, CO conversion of the other catalysts is similar regardless of the type of reactor. However, the yield of light olefins in the range of C₂–C₄ hydrocarbons and clean fuels is closely related to the formation of active iron carbide species and to surface acidity. The impregnated K/FeO_x catalyst is found to be one of the promising catalysts to be applied in a bubbling fluidized-bed reactor for middle temperature FTS reaction due to its high resistance to catalyst attrition with a high catalytic performance.

Keywords: Fischer–Tropsch synthesis; Iron-based catalyst; Light olefin; Clean fuel; Fixed-bed reactor; Bubbling fluidized-bed reactor

Synthesis, characterization, and photocatalytic properties of Ag modified hollow SiO₂/TiO₂ hybrid microspheres by Wei Zhao; Lili Feng; Rong Yang; Jie Zheng; Xingguo Li (pp. 181-189).

Display Omitted▶ Ag modified hollow SiO₂/TiO₂ hybrid spheres. ▶ High surface area and small particle size of the photocatalyst. ▶ Dye sensitization. ▶ Effective degradation of RhB under visible light irradiation.Well-defined Ag modified hollow SiO₂/TiO₂ hybrid spheres were successfully prepared through a two-step hydrothermal synthesis based on polystyrene templates followed by calcination. The employed protocol involves successive coating of the functionalized polystyrene (PS) template with SiO₂ and TiO₂ layers, followed by Ag doping using AgNO₃ as the Ag source. Finally, a calcination process is carried out for the elimination of the PS core, thermal decomposition of AgNO₃ to yield Ag nanoparticles and crystallization of the amorphous TiO₂ layer simultaneously to acquire the final products. With this method, a complete, homogeneous and smooth hollow SiO₂/TiO₂ hybrid structure with uniformly dispersed Ag nanoparticles was formed. Photocatalytic properties of the fabricated Ag modified hollow SiO₂/TiO₂ hybrid spheres has been investigated for the degradation of rhodamine B (RhB). Ag deposition significantly enhanced the RhB photodegradation under visible light irradiation due of the Schottky barrier formed at the Ag–TiO₂ interface, which serve as the electron trap, facilitating the separation of electrons and holes.

Keywords: Key words; TiO; ₂; Hollow spheres; Ag modified; Photocatalysis

Ozonation of model organic compounds catalysed by nanostructured cerium oxides by Carla A. Orge; José J.M. Órfão; Manuel F.R. Pereira; Andréa M. Duarte de Farias; Raimundo C. Rabelo Neto; Marco A. Fraga (pp. 190-199).

Display Omitted► Nanoflower, nanocube and nanoparticles ceria-shaped catalysts. ► Nanocatalysts for ozonation of organic compounds in water. ► The nanostructure determines the concentration of surface redox couple sites. ► Nanoparticle and nanocube shaped ceria performed best for ozonation of oxalic acid.Cerium oxides prepared by the precipitation method and hydrothermal synthesis, with distinct morphologies and particle size, were tested as catalysts in the ozonation of selected organic compounds. Oxalic acid, aniline and a reactive dye were used as representative of organic pollutants. In the case of oxalic acid, an increase in the catalytic activity with the increase of the percentage of Ce(III) on the surface was observed. Both single and catalytic ozonation allowed the total removal of aniline after 30min of reaction; the cerium oxide prepared by the precipitation method was the best catalyst for promoting the mineralization of aniline solutions. TOC removals close to 100% were obtained in all cases when cerium oxides were used as catalysts in the ozonation of the reactive dye tested.

Keywords: Cerium oxide; Nanocube; Nanoparticles; Nanostructure; Catalytic ozonation

ZnO/La₂O₂CO₃ layered composite: A new heterogeneous catalyst for the efficient ultra-fast microwave biofuel production by Lei Jin; Yashan Zhang; James P. Dombrowski; Chun-Hu Chen; Anthony Pravatas; Linping Xu; Christopher Perkins; Steven L. Suib (pp. 200-205).

Display Omitted▶ First example of low temperature active heterogeneous catalysts for environmentally friendly biodiesel production without a leaching problem. ▶ New and simple synthesis method for preparing La₂O₂CO₃ layered materials. ▶ No leaching of Zn or La was found in the biodiesel product. ▶ First time reporting La₂O₂CO₃ layered materials as active catalyst for transesterification reaction. ▶ Rapid reaction time for almost complete biodiesel conversion (5min) at low reaction temperatures (85°C).The search for solid state materials with high catalytic activities and with no leaching into the reaction medium is one of the key steps toward reducing the cost of producing biodiesel. We report a high biodiesel yield (>95%) in less than 5min under mild reaction conditions (<100°C) on a ZnO/La₂O₂CO₃ heterogeneous catalyst, showing no catalyst leaching into the reaction medium. The ZnO/La₂O₂CO₃ catalyst is prepared by a co-precipitation method and characterized by X-ray diffraction (XRD), thermogravimetric analyses (TGA), transmission electron microscopy (SEM), and transmission electron microscopy (TEM). The fatty acid methyl ester (FAME) yields as function of different amounts of catalyst was also investigated. Less than 1.0wt.% catalyst can be used in the reaction to get higher than a 95% FAME yield under mild reaction conditions. The catalytic performance is maintained after storing the catalyst in Ar for a month and no catalyst leaching into the products was found based on XRF analysis. The catalyst has a higher reaction rate than the homogeneous KOH catalyst with the assistance of microwave irradiation. All of these results promote the industrial application of the synthesized ZnO/La₂O₂CO₃ as an ideal catalyst for fast biodiesel production, avoiding many of the issues found in both commercial and independently published catalysts.

Keywords: Heterogeneous catalyst; Biodiesel; Low temperature; Leaching; Biofuel

Dispersion, reduction and catalytic performance of CuO supported on ZrO₂-doped TiO₂ for NO removal by CO by Chuanzhi Sun; Jie Zhu; Yuanyuan Lv; Lei Qi; Bin Liu; Fei Gao; Keqin Sun; Lin Dong; Yi Chen (pp. 206-220).

Display Omitted► The dispersion capacity (DC) of copper oxide on the surface of TZ is about 1.1mmol CuO/100m² TZ, which is basically in agreement with the value predicted by the incorporation model. When the CuO loadings are lower than DC, the activities increase very fast with the amounts of CuO increasing, whereas when the CuO loadings are higher than DC, the activities increase very slowly, implying that the crystalline copper oxide species on TZ support take low effect for the NO+CO reaction. ► Compared with the copper oxides supported on pure TiO₂ and ZrO₂ surface-modified TiO₂, copper oxides supported on ZrO₂-doped TiO₂ exhibit significantly different reduction properties. ► The ZrO₂ doping improves the adsorption stability of NO_x, which is an important factor of NO conversion. ► Cu-TZ catalysts have superior activity and selectivity to common Cu–TiO₂ catalysts for the NO+CO reaction.CuO catalysts supported on ZrO₂-doped TiO₂ (hereafter denoted as TZ) and pure anatase TiO₂ were characterized by HRTEM, XRD, UV–vis DRS, TPR, XPS, in situ FT-IR and activity test for the removal of NO by CO. The results indicate that: (1) CuO species can be highly dispersed on the surface of TZ support, and the dispersion capacity (DC) is about 1.1mmol/100m² TZ, which can be explained by the incorporation model. (2) The reduction temperature of CuO supported on TZ is lower than that supported on pure anatase TiO₂, ZrO₂ and ZrO₂ surface-modified anatase TiO₂ supports. Furthermore, the activity of Cu-TZ is also the highest among them measured by a relative turn over frequency (TOF) value of NO. (3) The ZrO₂ doping into TiO₂ improves the adsorption stability of NO_x (especially the bridged nitrate/nitro) and decreases the active temperature of Cu⁺–CO species, both of which are the key intermediates for NO conversion. On the other hand, the ZrO₂ doping into TiO₂ promotes the formation of Cu⁺/Cu⁰ species at high temperatures, which has a crucial effect on N₂O reduction.

Keywords: Cu-TZ; Cu–TiO; ₂; NO; +; CO reaction; In situ FT-IR; N; ₂; O; Nitrate

Highly dispersed Ag nanoparticles on modified carbon nanotubes for low-temperature CO oxidation by Yong-Ming Dai; Tsung-Chi Pan; Wen-Jay Liu; Jih-Mirn Jehng (pp. 221-225).

Display Omitted► A simple and easy method has been used to deposit highly dispersed Ag nanoparticles (NPs) on CNTs through functionalized of the carbon nanotubes (FCNTs). ► This is an important process for obtaining a highly dispersed Ag NPs on the FCNTs due to the presence of the surface oxygen-containing functional groups. ► The Ag NPs and their dispersion can enhance the efficiency of the CO oxidation reaction. ► These results imply that the Ag/FCNTs composites have a potential application in CO oxidation reaction at lower temperature.This study used a simple and easy method to prepare a highly dispersed Ag nanoparticles (NPs) on modified carbon nanotubes (MCNTs). The Ag NPs were easily attached to the MCNT support by anchoring them to the functional groups. Oxygen functionalities on the HNO₃-activated MCNT wall (FCNTs) provide nucleation centers for metal ions and can stabilize metal NPs on the support surface. This is an essential process for obtaining highly dispersed Ag NPs on FCNTs due to the presence of surface oxygen-containing functional groups. In addition, an Ag NP active site with a smaller particle size and higher dispersion rate exhibits higher activity for CO oxidation at low reaction temperatures. The catalytic results suggest that the Ag/FCNTs catalysts have a high potential for application in low-temperature CO oxidation.

Keywords: Modified carbon nanotubes (MCNTs); Functional groups; Ag nanoparticles; Low temperature CO oxidation

Low irradiance toluene degradation activity of a cementitious photocatalytic material measured at constant pollutant concentration by a successive approximation method by Alberto Strini; Luca Schiavi (pp. 226-231).

.Display Omitted► The successive approximation method allows activity measurements at predefined and constant concentration. ► The proposed measurement method allows the direct degradation rate comparison. ► The presented calibration method corrects the irradiance measurements for the radiometer spectral sensitivity. ► The toluene degradation activity of a titania cement material is measured at low irradiance. ► Evidences of non-linear irradiance-activity relationship at ambient irradiance and concentration levels are observed.Photocatalytic materials for air depollution have received increasing attention in the last years, particularly for outdoor applications where the sun is used as freely accessible UV-A source. The naturally available irradiance at an outdoor catalytic material surface is, however, extremely variable according to the time of the day, the season and the local weather. The relationship between irradiance and activity is therefore of great importance in the characterization of a photocatalytic depolluting material. This work illustrates the investigation carried out on the toluene photodegradation activity of a cementitious photocatalytic material versus the UV-A irradiance in the 100–850μWcm⁻² range. The photoactivity measurements were carried out using a stirred flow reactor. A specific successive approximation method was developed in order to bring all activity measurements to the same predefined pollutant concentration ensuring uniform conditions across the experiment. The study was repeated at four different pollutant concentrations lying between 0.25 and 1.0μmolm⁻³, showing evidences of a non-linear behaviour at low irradiances. A correction method for the irradiance measurement is also described, allowing the adjustment for the error caused by the specific spectral sensitivity of the utilized radiometric sensor.

Keywords: Activity/irradiance relationship; Constant concentration activity measurement; Radiometer spectral sensitivity correction; Cementitious photocatalytic material; Toluene air depollution

The influence of the local structure of Fe(III) on the photocatalytic activity of doped TiO₂ photocatalysts—An EXAFS, XPS and Mössbauer spectroscopic study by Éva G. Bajnóczi; Nándor Balázs; Károly Mogyorósi; Dávid F. Srankó; Zsolt Pap; Zoltán Ambrus; Sophie E. Canton; Katarina Norén; Ernő Kuzmann; Attila Vértes; Zoltán Homonnay; Albert Oszkó; István Pálinkó; Pál Sipos (pp. 232-239).

▪.► Fe-doped TiO₂ samples were prepared with sol–gel and flame synthesis. ► For sol–gel samples, photocatalytic activity passes through a maximum with the Fe-content. ► For the flame synthesised samples, Fe-doping deactivated them. ► Local structure of Fe(III) was found to be different in the two series. ► Presence of vacancies and haematite-like local structure was found to be beneficial for the photocatalytic performance.Fe(III)-doped TiO₂ based heterogeneous photocatalysts were prepared by the sol–gel technique (S samples) or flame hydrolysis (F samples). In photocatalytic phenol decomposition, the undoped F-sample performed much better, than the undoped S one. However, for the S samples, photocatalytic activity first increased with the increasing Fe(III) concentration, and then passed through a maximum, while Fe(III)-doping in F samples significantly decreased it, even at the smallest dopant level. Since the same dopant caused opposite photocatalytic effects in the two series, their structure was systematically compared to identify the underlying chemical and/or physical reasons.The photocatalysts were first characterized by AAS, DRS, XRD and TEM methods and it has been shown that the differences in the photocatalytic activity cannot be explained by the minor variations in the bulk structural properties of TiO₂.Mössbauer and XP spectroscopic measurements performed on representative samples qualitatively proved that the local structure of Fe(III) is different in the two series. To quantify these effects, Fe-K edge X-ray absorption measurements were performed. From the pre-edge and XANES region it was learnt that Fe(III) was present in a distorted octahedral environment in both series, however, the extent of distortion is much more significant within the S than within the F one. Information obtained from the EXAFS region indicated that the structure of Fe₂O₃ was much more ordered in the F-series then in the S one and vacancies were more abundant in the S than in the F series. Moreover, the geometry around Fe(III) systematically varied within the S-series, which could explain, why photocatalytic activity passed through a maximum with the increasing Fe(III) concentration in these samples.

Keywords: TiO; ₂; Fe(III) doping; EXAFS; XPS; Mössbauer; Local structure; Photocatalysis

Carbon auto-doping improves photocatalytic properties of biotemplated ceramics by Kai Gutbrod; Peter Greil; Cordt Zollfrank (pp. 240-245).

Display Omitted► Carbon can be doped automatically into the titania lattice during biotemplating. ► Band edge shift into VIS range by carbon auto-doping into the titania lattice. ► Carbon auto-doping increases the photocatalytic activity of titania. ► 800°C is the optimum temperature for the preparation of biotemplated photocatalysts.Biotemplated porous ceramics based on titania are promising candidates for the photo induced degradation of organic compounds in polluted streaming media, such as water or gas vapors. Reactors in various shapes can easily be produced by stringing a natural tissue template. Porous biotemplated ceramics were processed by vacuum infiltration of a titanium(IV)-isopropoxide-based sol into freeze dried stems of soft rush ( Juncus effuses) and subsequent calcination between 400 and 800°C. The solution of carbon in titania during calcination drastically improved the surface dependent photocatalytic activity, which was evaluated in comparison to commercially available titania powders. The biotemplated ceramics calcined below 600°C showed the anatase phase, whereas calcination at higher temperatures leads to a mixture of anatase and rutile. The carbon content as measured by energy dispersive X-ray spectroscopy was reduced from 31.0mol% after calcination at 400°C–1.6mol% after calcination at 800°C. The auto-formation of Ti–OC/Ti–OCO bonds due to the temperature induced substitution of oxygen atoms by carbon atoms from the biotemplate and the formation of interstitial carbon was verified by X-ray Photoelectron Spectroscopy measurements. The lowest band edge energy, calculated from UV/vis-spectrometry measurements was found at 419nm (2.96eV) for the biotemplated samples calcined at 800°C. The specific surface varied between 0.5m²/g and 45m²/g.

Keywords: Photocatalysis; Carbon auto-doping; Titanium dioxide; Biotemplating

Optimized water treatment by combining catalytic Fenton reaction using diamond supported gold and biological degradation by Roberto Martín; Sergio Navalon; Mercedes Alvaro; Hermenegildo Garcia (pp. 246-252).

Display Omitted► A new heterogeneous Fenton catalyst based on diamond supported gold nanoparticles is used. ► Chemical Fenton treatment is combined with biodegradation for treatment of phenol aqueous solutions. ► The Fenton reaction has been used to increase the biodegradability of bioreluctant phenol solutions. ► Lack of ecotoxicity and toxicity versus Vibrio Fisheri after mild Fenton treatment is achieved.Recently it has been reported that gold nanoparticles supported on Fenton treated diamond nanoparticles (Au/DNP) is a highly efficient catalyst to promote the generation of hydroxyl radicals from H₂O₂ [S. Navalon, R. Martin, M. Alvaro, H. Garcia, Angew. Chem. Int. Ed. 49 (2010) 8403–8407]. In the present work we have optimized a series of experimental parameters including initial pH, reaction temperature, H₂O₂ concentration, phenol to gold mol ratio and oxygen pressure to achieve biodegradability of aqueous phenol solutions with the minimum H₂O₂ concentration and attain a complete lack of toxicity (determined by the Vibrio fischeri bioluminescence assay). The results presented show how to combine mild Fenton degradation of bioreluctant phenol with consecutive biological treatment in such a way that the amount of H₂O₂ is kept to the minimum value. It was determined that the best conditions are pH 4, 50°C, H₂O₂ to phenol molar ratio 4 and 320mgL⁻¹ (1wt% Au) catalyst under oxygen atmosphere. Au/DNP exhibits a remarkable stability under these conditions and can be used up to four times without observing any loose of catalytic activity as determined by the temporal profiles of phenol degradation and H₂O₂ decomposition.

Keywords: Gold nanoparticles supported on diamond nanoparticles; Heterogeneous Fenton reaction; Waste water biodegradability; Vibrio fischeri; toxicity; Phenol degradation

Facile fabrication of hollow Pt/Ag nanocomposites having enhanced catalytic properties by Mee Rahn Kim; Dong Ki Lee; Du-Jeon Jang (pp. 253-260).

Display Omitted► Hollow Pt/Ag composite nanospheres show highly enhanced catalytic properties. ► Hollow Pt/Ag nanospheres have been prepared through a galvanic replacement reaction. ► Hollow Pt/Ag nanostructures catalyze the degradation of rhodamine B efficiently in the presence of KBH₄. ► Their catalytic performances depend highly on the sizes of the nanostructures.Hollow Pt/Ag composite nanospheres, which show highly enhanced catalytic properties, have been prepared through a galvanic replacement reaction of silver nanoparticles dispersed in Pt n⁺-added water. Pt n⁺, prepared in advance by the partial reduction of Pt⁴⁺ with weak reducing agents, is readily reduced galvanically to form porous Pt shells, and concomitantly produced Ag⁺ diffuses out to produce hollow Pt/Ag nanocomposites finally. The residual silver has been further eliminated from the composites with 0.5M HNO₃(aq) to produce hollow Pt nanospheres. Hollow Pt/Ag composite nanostructures have been found to catalyze the degradation of rhodamine B efficiently in the presence of KBH₄, although their catalytic performances depend highly on the metals, sizes, and shapes of the nanostructures.

Keywords: Catalysis; Galvanic displacement; Nanocomposite; Silver; Platinum

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Applied Catalysis B, Environmental (v.103, #1-2)