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Applied Catalysis B, Environmental (v.119-120, #)

Contents (pp. co4).

Editorial Board (pp. co2).

Editorial Board (pp. i).

Contents (pp. i).

Ni/Al coprecipitated catalysts modified with magnesium and copper for the catalytic steam reforming of model compounds from biomass pyrolysis liquids by F. Bimbela; D. Chen; J. Ruiz; L. García; J. Arauzo (pp. 1-12).

Display Omitted► Copper as a promoter of coprecipitated NiAlMg catalysts tested in steam reforming of bio-oil model compounds. ► Copper shows a positive effect on removing encapsulating coke in catalytic steam reforming of acetic acid with S/C=5.6. ► Stable performance using 5% Cu catalyst with acetic acid (S/C=5.6) during 12h at a short space time. ► Higher performance of 0%Cu catalyst in steam reforming of acetic acid (S/C=14.7), acetol and butanol.Ni/Al coprecipitated catalysts modified with magnesium and copper have been prepared by a constant pH technique and tested in the catalytic steam reforming of model compounds (acetic acid, acetol and butanol) from biomass pyrolysis liquids at 650°C and atmospheric pressure. Catalysts with different copper contents, reduced at 650°C for 1h, were tested in the steam reforming of acetic acid with a steam/carbon (S/C) molar ratio of 5.6. The best performance and the highest hydrogen yield in these conditions were achieved with the 5% Cu catalyst. This catalyst reduced at 650°C during 10h showed a high activity, close to the thermodynamic equilibrium, and a stable performance during 12h in the steam reforming of acetic acid with a S/C=5.6, using a short space time of 1.00g catalystmin/g acetic acid. Copper as a promoter produces counterbalanced effects: a decrease in the initial reforming activity and an enhancement of the catalyst stability. The initial steam reforming activity decreased and the CH₄ yield increased concurrently with increasing the copper content, because of the Ni dilution effect. Copper has a positive effect inhibiting the formation of encapsulating coke, identified as the cause for deactivation in acetic acid steam reforming with a steam-to-carbon molar ratio (S/C) of 5.6. However, such a positive effect of copper has not been observed in acetic acid steam reforming with S/C=14.7 or in the steam reforming of acetol and butanol.

Keywords: Hydrogen; Bio-oil; Steam reforming; Nickel; Copper; Coprecipitated catalyst

Ultra-deep desulfurization via reactive adsorption on Ni/ZnO: The effect of ZnO particle size on the adsorption performance by Yuliang Zhang; Yongxing Yang; Hongxian Han; Min Yang; Lu Wang; Yongna Zhang; Zongxuan Jiang; Can Li (pp. 13-19).

Display Omitted► Both the desulfurization activities and the sulfur capacities of the Ni/ZnO adsorbents with smaller particle sizes are enhanced noticeably. ► The Ni/ZnO adsorbent with smaller ZnO particle size could remove sulfur at a lower operating temperature. ► The apparent activation energy of desulfurization via Ni/ZnO adsorbent with smaller ZnO particle size is much lower.The effect of ZnO particle size on the adsorptive desulfurization performance for Ni/ZnO (5wt% NiO) adsorbent was investigated using thiophene as a sulfur containing compound in model gasoline with a fixed bed reactor. The Ni/ZnO adsorbents with different ZnO particle sizes (8, 12, 20, 30nm) were prepared by an impregnation method and characterized by powder X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and transmission electron microscopy (TEM). It was found that the adsorption capacity of the Ni/ZnO adsorbent for thiophene significantly increased with the decrease of the ZnO particle sizes. Typically at a breakthrough sulfur level of 1mg/L, sulfur capacity of Ni/ZnO (8nm) from model gasoline (500mg/L) is much higher than that of Ni/ZnO (30nm) from 84mg sulfur per gram adsorbent to nearly 0mg sulfur per gram adsorbent. This higher desulfurization activity and sulfur capacity for Ni/ZnO with smaller ZnO particle sizes could be derived from higher Ni dispersion on ZnO and lower mass transfer limitations of sulfur to ZnO from Ni in H₂.

Keywords: Adsorptive desulfurization; Ni/ZnO adsorbent; Size effect

Lysine-aided PMMA-templating preparation and high performance of three-dimensionally ordered macroporous LaMnO₃ with mesoporous walls for the catalytic combustion of toluene by Yuxi Liu; Hongxing Dai; Yucheng Du; Jiguang Deng; Lei Zhang; Zhenxuan Zhao (pp. 20-31).

By using the PEG- and/orl-lysine-aided PMMA-templating strategy, we prepared three-dimensionally ordered macroporous (3DOM) LaMnO₃ with mesoporous skeletons. It is found that the excellent catalytic performance of porous LaMnO₃ for toluene combustion was associated with the high surface area and oxygen adspecies concentration, good low-temperature reducibility, and unique bimodal pore structure.Display Omitted► 3DOM LaMnO₃ with mesoporous walls are prepared byl-lysine-aided PMMA-templating method. ►l-Lysine addition is critical in the formation of 3DOM structure with mesoporous skeletons. ► Bimodal porous LaMnO₃ possess high surface area and oxygen adspecies content and good reducibility. ► 3DOM LaMnO₃ with mesoporous walls perform excellently in the combustion of toluene. ► Catalytic activity is related to surface area, oxygen adspecies, reducibility, and bimodal pore structure.Rhombohedrally crystallized three-dimensionally ordered macroporous (3DOM) perovskite-type oxides LaMnO₃ with mesoporous skeletons were prepared using the poly(ethylene glycol) (PEG)- and/orl-lysine-assisted poly(methyl methacrylate) (PMMA)-templating method. Physicochemical properties of the materials were characterized by numerous analytical techniques. Catalytic performance of the as-prepared LaMnO₃ samples was evaluated for the combustion of toluene. It is found that addition of appropriate amounts of PEG400 andl-lysine was beneficial for the generation of high-quality 3DOM-structured LaMnO₃ (denoted as LaMnO₃-PL-1, LaMnO₃-PL-2, and LaMnO₃-PL-3 derived with a PEG400/l-lysine molar ratio of 1.23, 0.61, and 0.31, respectively) with mesoporous skeletons and high surface areas (32–38m²/g). Among the LaMnO₃ samples, the LaMnO₃-PL-2 one possessed the largest surface area and the highest contents of surface Mn⁴⁺ and adsorbed oxygen species. 3DOM-structured LaMnO₃ showed better low-temperature reducibility than bulk LaMnO₃, with the LaMnO₃-PL-2 sample displaying the best low-temperature reducibility. Under the conditions of toluene concentration=1000ppm, toluene/O₂ molar ratio=1/400, and space velocity=20,000mL/(gh), the porous LaMnO₃ catalysts remarkably outperformed the nonporous bulk counterpart; over the best-performing LaMnO₃-PL-2 catalyst, the temperatures required for toluene conversion=50 and 90% were ca. 226 and 249°C, respectively. The apparent activation energies (58–61kJ/mol) for toluene combustion over the LaMnO₃-PL-1–3 catalysts were much lower than that (97kJ/mol) over the bulk LaMnO₃ catalyst. It is concluded that the large surface area, high oxygen adspecies content, good low-temperature reducibility, and unique bimodal pore structure were responsible for the good performance of 3DOM-architectured LaMnO₃ with mesoporous skeletons for toluene combustion.

Keywords: Surfactant-assisted poly(methyl methacrylate)-templating method; Three-dimensionally ordered macroporous perovskite-type oxide; Lanthanum manganite; Mesoporous skeletons; Toluene combustion

Photolytic and photocatalytic degradation of fluoroquinolones in untreated river water under natural sunlight by Michela Sturini; Andrea Speltini; Federica Maraschi; Antonella Profumo; Luca Pretali; Epelde Aitziber Irastorza; Elisa Fasani; Angelo Albini (pp. 32-39).

Display Omitted► The photo(cata)lytic degradation of fluoroquinolones is studied in untreated river water. ► Realistic amounts (μgL⁻¹) of drugs are quickly removed (15min) from the matrix. ► Photocatalysis operates despite the presence of non-target matrix constituents. ► Fluoroquinolones byproducts are themselves photodegraded. ► TiO₂ photocatalysis is a convenient procedure for fluoroquinolones remediation.The photodegradation of some among the most frequently prescribed fluoroquinolone antibacterials (FQs) was investigated in untreated river water under solar light as well as under the same conditions in the presence of suspended TiO₂. The drugs considered included ciprofloxacin (CIP), danofloxacin (DAN), enrofloxacin (ENR), levofloxacin (LEV), marbofloxacin (MAR) and moxifloxacin (MOX), the last two belonging to the most recent FQ generation. The experiments were carried out in lab-scale batch reactor at concentrations (20–50μgL⁻¹) comparable to those actually measured in surface waters, and the course of the reaction was monitored by high pressure liquid chromatography (HPLC) with fluorescence detector (FD). A first order kinetics was obeyed upon both direct photolysis and TiO₂ heterogeneous photocatalysis. The photoproduced intermediates were identified by HPLC with electrospray ionization tandem mass spectrometry (ESI-MS/MS) and the degradation paths were identified. It was concluded that direct irradiation caused fluorine substitution and reductive elimination, while photocatalysis caused oxidative degradation of the amine side-chain (most efficient with tertiary amines and five-membered cyclic amines). The latter one was a minor process upon direct photolysis and involved hydrogen abstraction by excited states or photoproduced radicals. Photocatalytic decomposition occurred at a rate from two to five times faster than direct photolysis for all of the drugs, except for CIP, that is roughly proportional to the amine oxidation potential. The kinetic constants ranged from 0.061 to 0.66min⁻¹ in direct photolysis, from 0.22 to 2.78min⁻¹ in the presence of TiO₂. In the latter process, a 90% abatement of the concentration of these otherwise highly persistent drugs was obtained in ca. 15min. This supports the contention that TiO₂ photocatalysis under solar light is a convenient and efficient method for the remediation of pollutants at the μgL⁻¹ levels despite the presence of other non-target matrix constituents. Noteworthy, TiO₂ side-chain photo-oxidation was equally effective in the further degradation of the primary intermediates at a rate comparable to that of the parent compounds. The degradation proceeded further so that it could be expected that the antimicrobial activity, related to the FQ quinolone core more than to the substituent pattern, could be effectively eliminated.

Keywords: Abbreviations; AOP; advanced oxidation process; ACN; acetonitrile; CIP; ciprofloxacin; DAN; danofloxacin; DOM; dissolved organic matter; ENR; enrofloxacin; ESI-MS/MS; electrospray ionization tandem mass spectrometry; FD; fluorescence detector; FQs; fluoroquinolones; HPLC; high pressure liquid chromatography; LEV; levofloxacin; MAR; marbofloxacin; MOX; moxifloxacinFluoroquinolone; Photocatalysis; Photodegradation; Sunlight; Titanium dioxide

Electrocatalytic oxidation of glycerol on Pt/C in anion-exchange membrane fuel cell: Cogeneration of electricity and valuable chemicals by Zhiyong Zhang; Le Xin; Wenzhen Li (pp. 40-48).

Display Omitted► Pt/C with a small diameter (2.5nm) and narrow distribution (2–4nm) was synthesized. ► Chemicals and electricity cogeneration from glycerol in fuel cell was demonstrated. ► Valuable tartronic acid (50%) was produced on Pt/C catalyst in alkaline solution. ► Potential can regulate the product distribution of glycerol electro-oxidation. ► The concentrations of KOH and glycerol strongly affect oxidation product yields.Electrocatalytic oxidation of glycerol for cogenerating electricity and higher-valued chemicals on a Pt/C anode catalyst (2.4nm) in an anion-exchange membrane fuel cell (AEMFC) was investigated. The peak power density of an anion-exchange membrane – direct glycerol fuel cell (AEM-DGFC) with 1.0mg_Ptcm⁻² anode and non-PGM catalyst cathode can reach 124.5mWcm⁻² at 80°C and 58.6mWcm⁻² at 50°C, while the highest selectivity of C₃ acids (glyceric acid+tartronic acid) can reach 91%. The study found that higher pH reaction media could enhance fuel cell output power density (electricity generation) and selectivity of C₃ acids, while lower glycerol concentration could improve the selectivity of deeper-oxidized products (mesoxalic acid and oxalic acid). The fuel cell reactor with the Pt/C anode catalyst demonstrated an excellent reusability, and successfully obtained tartronic acid with a selectivity of 50% and mesoxalic acid with a selectivity of 7%, which are high compared to heterogeneous catalytic glycerol oxidation in batch reactors. It is found that the anode overpotential can regulate the oxidation product distribution, and that higher anode overpotentials favor CC bond breaking, thus lowering the C₃ acids selectivity. The reaction sequence of glycerol electro-oxidation detected in an electrolysis half cell with an on-line sample collection and off-line HPLC analysis agrees with the results obtained from single fuel cell tests. However, inconsistencies between the two systems still exist and are possibly due to different reaction environments, such as electrode structure, glycerol:catalyst ratio, and residence time of reactants.

Keywords: Glycerol oxidation; Cogeneration; Fuel cell; Valuable chemicals; Electrocatalysis

In-situ plasma regeneration of deactivated Au/TiO₂ nanocatalysts during CO oxidation and effect of N₂ content by Hong-Yu Fan; Chuan Shi; Xiao-Song Li; Shuo Zhang; Jing-Lin Liu; Ai-Min Zhu (pp. 49-55).

Display Omitted► Au/TiO₂ catalysts can be in-situ, rapidly and reversibly regenerated by O₂ plasma. ► N₂ addition caused an extra catalyst poisoning during plasma regeneration. ► The poisoning effect became much weaker at 80% N₂. ► The poisoning effect was mainly attributed to N₂O₅ formed in N₂/O₂ plasma.Driven by excellent CO oxidation capability of gold nanocatalysts at room temperature, a TiO₂ supported Au nanocatalyst (Au/TiO₂) was synthesized by deposition–precipitation method. To solve the deactivation issue of Au/TiO₂ catalyst during CO oxidation, in-situ regeneration by N₂/O₂ plasma was employed. Pure O₂ plasma could reversibly regenerate the deactivated Au/TiO₂ catalyst, however, N₂ addition resulted in an extra catalyst poisoning during regeneration. The extra poisoning effect was the most severe at 10% N₂ and became much weaker at 80% N₂. To investigate the formation of any surface poisoning species [NO_y]_s on Au/TiO₂ catalyst, gaseous product of N₂/O₂ plasma over fresh Au/TiO₂ catalyst was on-line analyzed by FT-IR, followed by catalyst characterization with temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The Au/TiO₂ catalysts before and after plasma regeneration were also measured by transmission electron microscopy (TEM), in order to exclude the poisoning effect arisen from the change in gold particle size or morphology.

Keywords: Gold catalyst; Deactivation; Plasma regeneration; N; ₂; content; CO oxidation

Selective dehydration of methanol to dimethyl ether on ZSM-5 nanocrystals by Ali A. Rownaghi; Fateme Rezaei; Matteo Stante; Jonas Hedlund (pp. 56-61).

Display Omitted► Study the influence of nanoscale crystal size, porosity and morphology of ZSM-5 on catalytic performance. ► Selective dehydration of methanol to dimethyl ether at mild conditions. ► The ZSM-5 nanocrystals showed methanol conversion and DME selectivity of 53% and 90% at 270°C, respectively. ► Development of catalyst with high resistance to coke formation.The effects of crystal size and mesoporosity on the performance of various synthesized ZSM-5 zeolites in catalytic dehydration of methanol to dimethyl ether (DME) reaction have been investigated. The reactions were carried out in a continuous flow fixed-bed reactor at temperatures between 180 and 320°C and 1.1bar. It was found that methanol conversion enhances by decreasing crystal size and increasing the reaction temperature. Uniform nanocrystal catalysts showed highest activity and stability for methanol dehydration to dimethyl ether in the temperature range studied. On the other hand, both the activity and selectivity of large crystals were low. The high activity and DME yield for the nanocrystals is due to smaller mass transport resistance for the Nano-ZSM-5 sample, due to the small crystal size. Furthermore, it was found that the selective dehydration of methanol to dimethyl ether on ZSM-5 catalyst is based on the product selectivity inside the pore channels; in other words, the selectivity to dimethyl ether should be 100% if there is no acid site on the external surface. From this evidence, it is concluded that in methanol dehydration to DME, the reaction activity is related to the crystal size, whereas the DME selectivity is determined by the uniformity of Al distribution, which determines acidity of external surface and low mass transport resistance of small crystal size. Therefore, a decrease in the number of acid sites on the external surface and reduction in crystal size are key ways to enhance catalytic selectivity and activity, respectively.

Keywords: ZSM-5 nanocrystals; Crystal size; External surface area and acidity; Methanol to dimethyl ether; Reaction temperature; Catalytic stability

Supported Co₃O₄-CeO₂ catalysts on modified activated carbon for CO preferential oxidation in H₂-rich gases by Ting Bao; Zhongkui Zhao; Yitao Dai; Xiaoli Lin; Ronghua Jin; Guiru Wang; Turghun Muhammad (pp. 62-73).

Display Omitted► Optimized Co₃O₄-CeO₂/AC may be a robust and promising catalyst for CO PROX reaction. ► The active species reducibility and dispersity strongly affect catalytic properties. ► H₂O₂ treatment markedly improves the catalytic activity of Co₃O₄-CeO₂/AC catalyst. ► Optimal component and preparation parameters are essential to Co₃O₄-CeO₂/AC. ► Formation of Co-Ce-O phase via Co–Ce interaction benefits for CO PROX reaction.CO preferential oxidation (PROX) reactions were performed over the supported Co₃O₄-CeO₂ catalysts on modified activated carbon (AC) for eliminating the trace CO from H₂-rich gases. The effects of support modification by H₂O₂ oxidation treatment, catalyst calcination temperature, Ce/Co atomic ratio ( n_Ce/Co), Co₃O₄-CeO₂ loading and reaction parameters on catalytic properties of the Co₃O₄-CeO₂/AC catalysts were investigated. Various characterization techniques like scanning electron microscopy (SEM), X-ray diffraction (XRD) and H₂ temperature-programmed reduction (H₂-TPR) were employed to reveal the relationship between catalysts nature and catalytic performance. Results illustrate that the supported Co₃O₄-CeO₂ catalyst on modified AC exhibits excellent catalytic properties, which highly depends on dispersity and reducibility of Co₃O₄ affected by the time of support treatment ( t_p), calcination temperature, n_Ce/Co and loading. The supported 35wt% Co₃O₄-CeO₂ catalyst (1:8 of n_Ce/Co) on the modified AC with H₂O₂ oxidation treatment for 6h demonstrates the best catalytic properties and the almost complete CO transformation takes place in a wide temperature range of 125–190°C. Moreover, it is also found that the developed catalyst exhibits an outstanding catalytic stability, and 100% CO conversion can be maintained as the time on stream evolutes up to 1800min even in the presence of CO₂ and H₂O in the feed. The optimized Co₃O₄-CeO₂/AC may be a robust and promising catalyst for eliminating trace CO from H₂-rich gases.

Keywords: Activated carbon; Modification; Cobalt oxide; Ceria; CO preferential oxidation; Hydrogen

Visible-light-activation of TiO₂ nanotube array by the molecular iron oxide surface modification by Yoshihiro Muramatsu; Qiliang Jin; Musashi Fujishima; Hiroaki Tada (pp. 74-80).

Display Omitted► TiO₂ nanotube arrays (NTA) were formed by a two-step anodization on Ti plate. ► The TiO₂-NTA shows a UV-light-activity comparable with that of TiO₂ particles. ► The surfaces of TiO₂-NTA were modified with molecular iron oxides. ► The iron oxide-surface modification significantly increases the UV-light-activity. ► The iron oxide-surface modification causes a high level of visible-light-activity.Uniform and adhesive TiO₂ nanotube arrays (TiO₂-NTAs) have been prepared by a two-step anodization in ethylene glycol solution containing NH₄F. The UV-light-activity of TiO₂-NTAs prepared by changing the electrolytic voltage and calcination temperature was studied for the degradation of 2-naphthol. Further, the surface of TiO₂-NTA has been modified with iron oxide species at a molecular scale by the chemisorption–calcination cycle technique. The iron oxide-surface modification endows TiO₂-NTA with a high level of visible-light-activity, concomitantly increasing the UV-light-activity. Under optimum conditions, the iron oxide-surface modified TiO₂-NTA exhibits a UV-light-activity comparable with that of highly active TiO₂ particles (P-25, Degussa).

Keywords: TiO; ₂; nanotube array; Iron oxide; Surface modification; Visible-light-photocatalyst; Environmental purification

Oxidation of ethylbenzene to acetophenone by a Mn catalyst supported on a modified nanosized SiO₂/Al₂O₃ mixed-oxide in supercritical carbon dioxide by M. Arshadi; M. Ghiaci; A. Rahmanian; H. Ghaziaskar; A. Gil (pp. 81-90).

Display Omitted► The Mn catalysts immobilized on functionalized nanosized SiO₂-Al₂O₃ used as catalysts. ► The Mn catalysts were studied in the oxidation of ethylbenzene to acetophenone. ► Without organic solvent in supercritical carbon dioxide. ► The conversion and selectivity reached to 91 and 98%, respectively. ► Electrochemical behavior of the Mn nanocatalysts was studied.The selective oxidation of ethylbenzene to acetophenone with tert-butyl hydroperoxide in the presence of an SiO₂/Al₂O₃-supported manganese catalyst occurs with a conversion of 91% and a selectivity of 98%, in the absence of an organic solvent, in supercritical carbon dioxide. The catalysts could be reused at least eight times without significant loss of activity. This procedure simplifies the isolation of the reaction products and has the advantage of using only carbon dioxide as a solvent under mild conditions. The electrochemical data for Mn nanocatalysts immobilized at the surface of multi-walled carbon nanotubes were also studied. The results indicate that the Mn catalysts anchored on the modified SiO₂/Al₂O₃ mixed-oxide via 2-aminoethyl-3-aminopropyltrimethoxysilane (2-AE-3-APTMS) have an easily oxidizable environment, lower oxidation potential and lower charge-transfer resistance, thus leading to a higher catalytic activity and selectivity than when 3-aminopropyltrimethoxysilane (3-APTES) is used.

Keywords: Supercritical carbon dioxide; Mn nanocatalyst; Ethylbenzene; Acetophenone; Oxidation

Effect of periodic lean/rich switch on methane conversion over a Ce–Zr promoted Pd-Rh/Al₂O₃ catalyst in the exhausts of natural gas vehicles by Djamela Bounechada; Gianpiero Groppi; Pio Forzatti; Kauko Kallinen; Toni Kinnunen (pp. 91-99).

Display Omitted► Rich pulses in a constant lean feed gas stabilize catalytic performances. ► Symmetric oscillations around λ=1.00 stabilize and enhance catalytic performances. ► Higher CH₄ conversions are obtained under rich than under lean conditions. ► The presence of O₂ in the rich phase plays a key role in CH₄ conversion enhancement. ► The activity enhancement is likely ascribable to a more active mixed PdO/Pd⁰ state.The behavior of a commercial Ce–Zr promoted Pd-Rh/Al₂O₃ catalyst for the abatement of methane from the exhausts of natural gas vehicles (NGVs) is studied in presence of large amounts of water under both stationary conditions and by periodically switching from lean to rich feed. Under stationary conditions with both stoichiometric ( λ=1.00) and lean ( λ=1.02) feed catalyst deactivation is observed after prolonged exposure to the reaction mixture. Periodic rich pulses in a constant lean feed gas result in the stabilization of catalytic performances.A higher methane conversion than those obtained with stoichiometric and lean feed mixtures is observed under rich conditions, during an experiment carried out by performing lean pulses ( λ=1.02) in a constant rich feed gas ( λ=0.98). The analysis of reactants conversion and products distribution suggests that different chemistries are involved under lean and rich conditions. Only reactions of complete oxidation of H₂, CO, CH₄ and NO occur under excess of oxygen, whereas under rich conditions NO reduction, CH₄ steam reforming and water gas shift also occur.The effect of symmetric oscillation of the exhausts composition around stoichiometry is also addressed by periodically switching from slightly rich to slightly lean composition with different oscillation amplitudes (Δ λ=±0.01, ±0.02 and ±0.03). Higher and more stable methane conversion performances are obtained than those observed under constant λ operations. The presence of a more active PdO/Pd⁰ state is suggested to explain the enhancement of catalytic performances.

Keywords: Natural gas vehicle; Methane oxidation; Pd/Rh-based catalyst; Periodic operation

The effect of the morphological characteristics of TiO₂ supports on the reverse water–gas shift reaction over Pt/TiO₂ catalysts by Sung Su Kim; Hyun Hee Lee; Sung Chang Hong (pp. 100-108).

Display Omitted► The Pt/TiO₂ catalyst shows a great activity in the RWGS reaction. ► Catalytic activity was highly dependent on TiO₂ support's reducibility. ► Reducibility of TiO₂ support was also dependent on TiO₂ crystallite size. ► TiO₂ crystallite size is a key factor in the RWGS reaction over Pt/TiO₂ catalyst.The effect of the morphological characteristics of a TiO₂ support on the reverse water–gas shift reaction over Pt/TiO₂ catalysts was examined. The activity of Pt catalysts with 6 different types of TiO₂ supports varied during the reverse water–gas shift reaction. Analysis using H₂ Temperature Programmed Reduction (TPR) and Temperature Programmed Desorption (TPD) confirmed that the active sites of the Pt/TiO₂ catalyst included both the Pt sites and the TiO₂ sites, which were reducible, and the difference in the activity of the Pt/TiO₂ catalysts was dependent on the reducibility of the TiO₂ supports. X-ray diffraction (XRD) analysis showed that the TiO₂ crystallite size was a key factor that dictated the reducibility of the TiO₂ sites.

Keywords: Pt; TiO; ₂; CO; ₂; RWGS; SMSI

Enhanced photocatalytic activity of hierarchical macro/mesoporous TiO₂–graphene composites for photodegradation of acetone in air by Wenguang Wang; Jiaguo Yu; Quanjun Xiang; Bei Cheng (pp. 109-116).

Hierarchical macro/mesoporpous TiO₂–graphene composites with low loadings (0.05wt.%) of graphene showed an enhanced photocatalytic activity in photodegradation of acetone in air.Display Omitted► Hierarchical macro/mesoporpous TiO₂–graphene composites with low loadings (0–0.2wt.%) of graphene were prepared. ► The prepared samples showed enhanced photocatalytic activity in photodegradation of acetone in air. ► At graphene content=0.05wt.%, the TiO₂–graphene composites exhibited the highest photocatalytic activity, which exceeds that of pure TiO₂ by a factor of 1.7. ► The transient photocurrent response experiment confirmed the transfer of photogenerated electrons from TiO₂ to graphene.Graphene, a single layer of graphite, possesses a unique two-dimensional structure, high conductivity, superior electron mobility and extremely high specific surface area, and can be obtained on a large scale at low cost. Thus, it has been regarded as an excellent catalyst support. Recently, graphene-based semiconductor photocatalysts have attracted more attention due to their enhanced photocatalytic activity. In this work, hierarchical macro/mesoporpous TiO₂–graphene composites with low loadings (0–0.2wt.%) of graphene were first produced by a simple one-step hydrothermal method using tetrabutyl titanate as the titanium precursor. The prepared composite samples presented enhanced photocatalytic activity in photodegradation of acetone in air. Graphene content exhibited an obvious influence on photocatalytic activity and the optimal graphene addition content was determined. At the optimal graphene concentration (0.05wt.%), the prepared composites showed the highest photocatalytic activity, exceeding that of pure TiO₂ and Degussa P-25 by a factor of 1.7 and 1.6, respectively. The enhanced photocatalytic activity is due to graphene as an excellent electron acceptor and transporter, thus reducing the recombination of charge carriers and enhancing the photocatalytic activity. The transient photocurrent response experiment further confirmed the transfer of photogenerated electrons from TiO₂ to graphene and the suggested mechanism.

Keywords: Hierarchical; Macro/mesoporous; Graphene; Titania; Photocatalytic activity

Identification of active sites for CO and CH₄ oxidation over PdO/Ce1−_xPd_xO2−_δ catalysts by Lian Meng; Jian-Jun Lin; Zhi-Ying Pu; Liang-Feng Luo; Ai-Ping Jia; Wei-Xin Huang; Meng-Fei Luo; Ji-Qing Lu (pp. 117-122).

Display Omitted► PdO/Ce1−_xPd_xO2−_δ contains surface PdO_x ( x=1–2) and Ce1−_xPd_xO2−_δ solid solution. ► Surface PdO_x are more active for CO oxidation than Pd⁴⁺ cations in Ce1−_xPd_xO2−_δ. ► Pd⁴⁺ cations in Ce1−_xPd_xO2−_δ are more active for CH₄ oxidation than surface PdO_x. ► A portion of Pd⁴⁺ in Ce1−_xPd_xO2−_δ transform to surface PdO_x at high temperature.A PdO/Ce1−_xPd_xO2−_δ catalyst containing surface PdO_x ( x=1–2) species and Ce1−_xPd_xO2−_δ solid solution was prepared by a solution combustion method. It was found that the surface PdO_x species could be removed by nitric acid treatment. Also, partial Pd⁴⁺ cations in the CeO₂ lattice migrated to the surface to form surface PdO_x species after high temperature calcination (500°C). The catalyst was tested for catalytic CO and CH₄ oxidation. For CO oxidation, the specific reaction rate of the surface PdO_x species (673.4μmolCOgPd−1 s−1) was 249 times as high as that of the Ce1−_xPd_xO2−_δ solid solution (2.7μmolCOgPd−1 s−1), due to the fact that the surface PdO_x species provided CO chemisorption sites. While for CH₄ oxidation, the specific reaction rate of the Ce1−_xPd_xO2−_δ solid solution (7.5μmolCH4gPd−1 s−1) was higher than that of the PdO/Ce1−_xPd_xO2−_δ catalyst (2.8μmolCH4gPd−1 s−1), due to the covered Ce1−_xPd_xO2−_δ surface by surface PdO_x species.

Keywords: PdO; _x; species; Ce; 1−; _x; Pd; _x; O; 2−; _δ; solid solution; Active site; Specific reaction rate; Acid treatment

N-doped carbon prepared by pyrolysis of dicyandiamide with various MeCl₂· xH₂O (Me=Co, Fe, and Ni) composites: Effect of type and amount of metal seed on oxygen reduction reactions by Chang Hyuck Choi; Sung Hyeon Park; Seong Ihl Woo (pp. 123-131).

Display Omitted► N-doped carbon was prepared as a catalyst towards oxygen reduction reaction. ► Co, Fe, and Ni chlorides were used as seeds for carbonization of dicyandiamide. ► The type of seed metal alters the degree of sp²-bonding of carbon. ► Increasing degree of sp²-bonding of carbon improves catalytic activity. ► Amount of seed precursor does not significantly affect the ORR activity.N-doped carbon was prepared from dicyandiamide as the source for both carbon and nitrogen. Dicyandiamide was pyrolyzed at 900°C on various metal chlorides (MeCl₂· xH₂O, Me=Co, Fe, and Ni) to clarify the effects of metal type on the properties of the N-doped carbon. The results showed that electrochemical and physical characteristics of the N-doped carbon were altered by the type of metal seed. The N-doped carbon from Co showed the best performance in oxygen reduction reactions (ORRs) and the order of ORR activity was N-doped carbon from Co>Fe>Ni. Raman and XPS studies revealed that the metal type during pyrolysis step determined degree of sp²-carbon network, and ORR activity of N-doped carbon was improved as the degree of sp²-carbon network increased. The effects of the amount of metal precursor on activity of ORRs and rate of H₂O₂ formation were faint but the carbonization yield of dicyandiamide increased as the amount of metal precursor increased. The catalysts optimized by altering the type and amount of metal seed showed a 0.60V (vs. Ag/AgCl) onset potential and a 42% oxygen reduction reactivity at 0.40V (vs. Ag/AgCl) compared to that of a commercial Pt/C catalyst.

Keywords: Nitrogen doped carbon; Oxygen reduction reaction; Metal seeds; Polymer electrolyte membrane fuel cells

Modelling photo-Fenton process for organic matter mineralization, hydrogen peroxide consumption and dissolved oxygen evolution by A. Cabrera Reina; L. Santos-Juanes Jordá; J.L. García Sánchez; J.L. Casas López; J.A. Sánchez Pérez (pp. 132-138).

Display Omitted► A kinetics model for TOC mineralization using the photo-Fenton process is proposed. ► The model shows predictive capabilities regarding dissolved oxygen evolution. ► Variable ranges were 4–25mM for TOC, 0.089–0.44mM for Fe²⁺ and 9–45mM for H₂O₂. ► The influence of light intensity was considered explicitly within the model. ► The model was later applied to a pollutant mixture successfully.A kinetics model with lumped components and TOC fractionation is proposed to track paracetamol degradation, as a model pollutant, using the photo-Fenton process. The proposed structure shows acceptable predictive capabilities regarding hydrogen peroxide consumption, TOC mineralization and dissolved oxygen evolution. The number of model parameters is considered assumable in calibrating other pollutants and degradation mixtures when applying this technology. This study covers a pollutant load range between 4 and 25mM of TOC. The Fe²⁺ initial load varied between 0.089 and 0.44mM whilst the initial H₂O₂ concentration tested ranged from 9mM to 45mM. The influence of light intensity was considered explicitly within the model whilst temperature and pH conditions were held constant. The fixed structure model, containing 9 kinetic parameters and 3 stoichiometric coefficients, was later applied to a pollutant mixture with a successful prediction of hydrogen peroxide and TOC profiles.

Keywords: Photo-Fenton kinetics; Dissolved oxygen; Paracetamol; Photocatalysis

Facile synthesis of tremelliform Co_0.85Se nanosheets: An efficient catalyst for the decomposition of hydrazine hydrate by Cheng-Cheng Liu; Ji-Ming Song; Jing-Feng Zhao; Hua-Jun Li; Hai-Sheng Qian; He-Lin Niu; Chang-Jie Mao; Sheng-Yi Zhang; Yu-Hua Shen (pp. 139-145).

Tremelliform Co_0.85Se nanosheets have been successfully synthesized by a hydrothermal reaction between Co(NO₃)₂·6H₂O and Na₂SeO₃ at 140°C free of any surfactants or templates. The as-prepared Co_0.85Se nanosheets have efficient catalytic decomposition for hydrazine hydrate at room temperature.Display Omitted► Tremelliform Co_0.85Se nanosheets with the thickness of ca. 10nm have been synthesized. ► A single Co_0.85Se nanosheet is single-crystalline structure. ► The Co_0.85Se nanosheets have high catalytic activity and reusability for decomposition of hydrazine hydrate at room temperature.Tremelliform Co_0.85Se nanosheets have been successfully synthesized through a hydrothermal reaction of Co(NO₃)₂·6H₂O, Na₂SeO₃ and N₂H₄·H₂O without using any surfactant or structure-directing agents. The hydrothermal reaction products were confirmed as pure phase of Co_0.85Se. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations further showed that the obtained products were flexible tremelliform nanosheets, which were composed of the slices with thickness of ca. 10nm. Additionally, detailed investigation indicated that the formation of the tremelliform Co_0.85Se nanosheets was strongly dependent on the reaction temperature, reaction time and reactant ratios. The obtained tremeliform Co_0.85Se nanosheets displayed ferromagnetic properties at room temperature according to the magnetic measurement. More interesting, the as-prepared Co_0.85Se nanosheets showed efficient catalytic performance for decomposition of hydrazine hydrate at room temperature. In addition, the stability and reversibility of Co_0.85Se nanosheets as catalysts are also excellent, indicating that these nanomaterials can be used as long term catalysts in wastewater treatment.

Keywords: Tremelliform; Cobalt selenide; Catalytic decomposition; Hydrazine hydrate; Hydrazine compounds

Effect of Au supported TiO₂ with dominant exposed {001} facets on the visible-light photocatalytic activity by Shuying Zhu; Shijing Liang; Quan Gu; Liyan Xie; Jixin Wang; Zhengxin Ding; Ping Liu (pp. 146-155).

Novel Au/TiO₂ nanosheet photocatalyst with dominant exposed {001} facets is successfully prepared for the first time. Compared with the other plasmonic photocatalyst Au/TiO₂, such as Au/P25, Au/anatase TiO₂, and Au/rutile TiO₂, our photocatalyst shows much higher photocatalytic activity for the degradation of RhB.Display Omitted► Novel Au/TiO₂ with dominant exposed {001} facets is successfully prepared. ► SPR effect of Au NPs ensures the catalysts work under the visible light irradiation. ► Au/TiO₂-001 samples show superior visible light photocatalytic activities for RhB. ► Relationship between photoelectric response and photoactivity was investigated. ► Roles of (001) facet on the photocatalysis and photoelectrochemistry are discussed.Novel visible-light-driven plasmonic photocatalyst Au/TiO₂ nanosheets with a high percentage of exposed {001} facets were fabricated by hydrothermal treatment of tetrabutyl titanate and hydrofluoric acid, followed by the polyol reduction process (denoted by Au/TiO₂-001). The prepared samples were characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, N₂-sorption, UV-vis diffuse reflectance spectroscopy, and photoluminescence spectra. The variations of photoelectric response after depositing Au nanoparticles (NPs) on TiO₂-001 nanosheets were investigated by the photoelectrochemical experiment. The results display that the Au NPs with average diameter of ca. 5nm were deposited on (001) facet of TiO₂ nanosheets in the form of metallic state. The samples exhibited a strong absorption in the visible light region due to the surface plasmon resonance (SPR) effect of Au NPs. For the photocatalytic degradation of rhodamine B (RhB) in aqueous solution, the Au/TiO₂-001 showed superior photocatalytic activities compared with bare TiO₂-001 and other Au deposited photocatalysts, such as Au/P25 (Degussa TiO₂), Au/anatase TiO₂, and Au/rutile TiO₂. The enhanced photocatalytic activities can be explained by its unique morphology, larger surface area, and smaller crystallite. Meanwhile, TiO₂ dominated {001} facets with higher electron mobility and better adsorption of pollutant molecule may be another reason for the higher photocatalytic activity. In addition, the Au NPs are believed to play an essential role in enhancing the photoreactivity because they are able to generate photoelectrons and enhance the visible light absorption intensity. The effects of the Au content, the calcination temperature of TiO₂-001, the supporter, and the reaction atmosphere on photocatalytic activities were investigated in detail. The decomposition mechanism of RhB over Au/TiO₂-001 under visible light irradiation and the active species in the photocatalytic process had also been discussed. It is hoped that our work could render guided information for steering toward the design and application of noble metal/semiconductor nanocompositions with high visible-light photocatalytic activity.

Keywords: TiO; ₂; nanosheets; Au nanoparticles; {0; 0; 1} facets; Plasmonic photocatalyst; Visible light

Photocatalytic activity of a porphyrin/TiO₂ composite in the degradation of pharmaceuticals by Sharon Murphy; Carla Saurel; Anne Morrissey; John Tobin; Michael Oelgemöller; Kieran Nolan (pp. 156-165).

Indoor (left) and solar photocatalytic reactions (right) showing the degradation of famotidine using TCPP–TiO₂ composite materials. TCPP–TiO₂-A (●) and -B (♦), photolysis (■) P-25 TiO₂ (▴). [TCPP–TiO₂] or [P-25 TiO₂]=0.031g, [FAM]=0.083mM.Display Omitted► Porphyrin/TiO₂ composite prepared via an adsorbed method of preparation. ► Porphyrin/TiO₂ composite tested on famotidine, tamsulosin and solifenacin. ► Elimination of famotidine with visible light superior than P-25 TiO₂. ► Composite was ineffective for tamsulosin and solifenacin. ► HPLC traces of famotidine photocatalytic experiments shows mineralisation is not occurring.Two separate methods were used to prepare a tetra(4-carboxyphenyl)porphyrin (TCPP)-TiO₂ composite. In method A TCPP was absorbed onto TiO₂ in methanol at room temperature, whilst in method B TCPP was absorbed onto TiO₂ in dimethylformamide (DMF) at reflux. Both composites exhibited the same physical and chemical characteristics as shown by FT-IR, SEM and UV–vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of both composites was then determined by HPLC monitoring of the photo-degradation of the pharmaceutical Famotidine under both visible and solar light irradiation. The recyclability of the composites was also examined by recovery of the composite post-reaction, although the absorbed TCPP was found to partially degrade, the recycled composite still exhibited catalytic behaviour. All reactions were monitored by HPLC which revealed that the photodegradation of Famotidine by the TCPP–TiO₂ composites does not lead to complete mineralisation, but instead generates a range of intermediates/products. Investigation of these products by LC–MS–MS and DI–MS analysis found that one major degradation product was formed, the S-oxide of Famotidine. The TCPP–TiO₂ composites were also screened in the photo-degradation of the pharmaceuticals tamsulosin and solifenacin using the optimised conditions developed for famotidine. However, the composites were found to be ineffective for the photo-catalytic degradation of these compounds, demonstrating that this class of composite are only effective for specific compounds.

Keywords: TiO; ₂; Tetra-(4-carboxyphenyl)porphyrin; Famotidine; Photocatalysis; Visible light

Palladium nanoparticles supported on manganese oxide–CNT composites for solvent-free aerobic oxidation of alcohols: Tuning the properties of Pd active sites using MnO_x by Hui Teng Tan; Yuanting Chen; Chunmei Zhou; Xinli Jia; Jixin Zhu; Jing Chen; Xianhong Rui; Qingyu Yan; Yanhui Yang (pp. 166-174).

Display Omitted► MnO_x–CNT composite was prepared via a facile grafting method. ► MnO_x acts as a “nano-ligand” to tune the properties of Pd active sites. ► Electronic interaction was enhanced due to the presence of MnO_x. ► MnO_x also improves the stability of Pd nanoparticles during the reaction. ► An excess amount of MnO_x leads to poor activity due to the strong of SMSI.The manganese oxide-multi-walled carbon nanotube (MnO_x/CNT) composite was successfully synthesized following a surface deposition method. Subsequently, the palladium nanoparticles were homogeneously deposited onto this MnO_x/CNT hybrid material followed by being reduced under H₂ atmosphere. The catalytic activity in solvent-free benzyl alcohol oxidation was correlated with MnO_x loading, indicating the important role of manganese oxide in tuning the properties of Pd catalytic active site, e.g., dispersion and electron density. In the presence of reducible MnO_x on CNT, the electron transfer and oxygen activation were greatly enhanced because of the synergistic interaction between Pd metallic nanoparticles and the hybrid support materials. Due to this strong metal support interaction (SMSI), the Pd/MnO_x/CNT catalysts were remarkably stable against deactivation.

Keywords: Manganese–CNT; Palladium; Solvent-free; Alcohol oxidation; SMSI

Nanostructured δ-FeOOH: An efficient Fenton-like catalyst for the oxidation of organics in water by Izabela S.X. Pinto; Pedro H.V.V. Pacheco; Jakelyne Viana Coelho; Eudes Lorençon; José D. Ardisson; José D. Fabris; Patterson P. de Souza; Klaus W.H. Krambrock; Luiz C.A. Oliveira; Márcio C. Pereira (pp. 175-182).

Display Omitted► δ-FeOOH with different surface areas and mesoporous structure is easily prepared. ► δ-FeOOH can activate H₂O₂ to produce highly reactive radical species. ► δ-FeOOH is efficient to promote oxidation of organics in the presence of H₂O₂.δ-FeOOH nanoparticles were prepared by the precipitation of Fe(OH)₂ followed by rapid oxidation with H₂O₂. Samples with different surface areas and particle sizes were obtained by controlling the final pH of the reaction medium. The samples were characterized by X-ray powder diffractometry,⁵⁷Fe Mössbauer spectroscopy, saturation magnetization measurements, total Fe chemical analyses and BET surface area measurements. The catalytic activities of these samples for H₂O₂ decomposition were strongly influenced by the δ-FeOOH surface area. EPR was used to monitor catalytic H₂O₂ decomposition in the presence of methanol, indicating that the mechanism of decomposition involves radicals in accord with the Haber–Weiss mechanism. Methylene blue and indigo carmine were used to simulate the degradation of contaminants. Monitoring these experiments with ESI-MS revealed that δ-FeOOH can activate H₂O₂ to produce reactive radicals, which can further promote the oxidation of the dyes. The dye degradation rates depended on the amount of Fe²⁺ generated in situ on the δ-FeOOH surface.

Keywords: Iron oxyhydroxide; Catalysis; Oxidation; Dyes; Fenton

NO_x storage and reduction properties of model ceria-based lean NO_x trap catalysts by Chuan Shi; Yaying Ji; Uschi M. Graham; Gary Jacobs; Mark Crocker; Zhaoshun Zhang; Yu Wang; Todd J. Toops (pp. 183-196).

Display Omitted► Model BaO- and CeO₂-containing LNT catalysts were prepared. ► The use of ceria as a support was beneficial for the dispersion of BaO. ► The presence of ceria improved catalyst regeneration at low temperature. ► Ceria was beneficial for NO_x storage capacity at 200°C and 300°C. ► A Pt/BaO/CeO₂/Al₂O₃ catalyst showed the best performance during lean-rich cycling.Three kinds of model ceria-containing LNT catalysts, corresponding to Pt/Ba/CeO₂, Pt/CeO₂/Al₂O₃ and Pt/BaO/CeO₂/Al₂O₃, were prepared for comparison with a standard LNT catalyst of the Pt/BaO/Al₂O₃ type. In these catalysts ceria functioned as a NO_x storage component and/or a support material. The influence of ceria on the microstructure of the catalysts was investigated, in addition to the effect on NO_x storage capacity, regeneration behavior and catalyst performance during lean/rich cycling. The Pt/Ba/CeO₂ and Pt/BaO/CeO₂/Al₂O₃ catalysts exhibited higher NO_x storage capacity at 200 and 300°C relative to the Pt/BaO/Al₂O₃ catalyst, although the latter displayed better storage capacity at 400°C. Catalyst regeneration behavior at low temperature was also improved by the presence of ceria, as reflected by TPR measurements. These factors contributed to the superior NO_x storage-reduction performance exhibited by the Pt/Ba/CeO₂ and Pt/BaO/CeO₂/Al₂O₃ catalysts under cycling conditions in the temperature range 200–300°C. Overall, Pt/BaO/CeO₂/Al₂O₃ (which displayed well balanced NO_x storage and regeneration behavior), showed the best performance, affording consistently high NO_x conversion levels in the temperature range 200–400°C under lean-rich cycling conditions.

Keywords: Ceria; Barium; Lean NO; _x; trap catalyst; Storage; Reduction

Preparation of the new polyaniline/ZnO nanocomposite and its photocatalytic activity for degradation of methylene blue and malachite green dyes under UV and natural sun lights irradiations by Volkan Eskizeybek; Fahriye Sarı; Handan Gülce; Ahmet Gülce; Ahmet Avcı (pp. 197-206).

Photodegradation of dyes under natural sunlightDisplay Omitted► The polyaniline matrix was synthesized first time in aqueous diethylene glycol solution medium. ► The ZnO nanoparticles were synthesized in de-ionized water by arc-discharge method. ► The photocatalytical activity of the PANI/ZnO nanocomposite under UV and natural sunlight irradiations were studied. ► The photocatalyst amount was used as lower with respect to literature but higher photodegradation rates have been obtained.A new polyaniline (PANI) homopolymer and PANI/ZnO nanocomposite have been successfully synthesized in aqueous diethylene glycol solution medium via the chemical oxidative polymerization of aniline. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, FTIR spectra, UV–vis spectroscopy measurements were used to characterize the resulting PANI homopolymer and PANI/ZnO nanocomposite photocatalysts. The photocatalytic activities of PANI homopolymer and PANI/ZnO nanocomposites were investigated by the degradation of methylene blue (MB) and malachite green (MG) dyes in aqueous medium under natural sunlight and UV light irradiation and the efficiency of the catalysts have been discussed in detail. Results indicate that the addition of the ZnO nanoparticles to the PANI homopolymer enhance the photocatalytic efficiency under natural sunlight irradiation and a little amount of PANI/ZnO nanocomposite photocatalyst (0.4g/L) degrades both of the dye solutions (MB or MG) with 99% efficiency after 5h of irradiation under natural sunlight.

Keywords: Polyaniline; ZnO; Polyaniline/ZnO nanocomposite; Photocatalysis; Natural sunlight; UV light

On the reducibility of sulfated Pt/Ce_XZr1−_XO₂ solids: A coupled thermogravimetric FT-IR study using CO as the reducing agent by P. Bazin; O. Saur; O. Marie; M. Daturi; J.C. Lavalley; A.M. Le Govic; V. Harlé; G. Blanchard (pp. 207-216).

Display Omitted► We propose a mechanism for sulfate reduction by CO over ceria–zirconia oxides using FTIR and ATG. ► The mechanism involves a migration step between bulk-like and surface sulfate species. ► The platinum promoting effect would be directly linked with the better oxide reducibility. ► The oxide reduction is always concomitant to the sulfates one. ► The higher OSC of sulfated Ce-based catalyst is due to the replacement of some oxygen by sulfur atoms.The reducibility of sulfate species by CO was studied over ceria and Ce_0.63Zr_0.37O₂ mixed oxide with or without platinum, using infrared spectroscopy and thermogravimetry. The mechanism for sulfate reduction appeared to be based on three main points. Firstly, the exchange between surface and bulk-like sulfate species is required. The sulfate reduction indeed occurs at the oxide surface and bulk-like species need to migrate toward the surface to be further reduced. Secondly, it was observed that surface sulfate species are more easily reduced by CO on the reduced oxide. Therefore, platinum loading which favors the oxide reduction, also favors the sulfate reduction by CO. Finally, the reduction of sulfated Pt-free samples occurs in only one step, which is linked to the own reducibility of the surface sulfate species, probably through a direct interaction with CO. The amount of sulfur stored from sulfate reduction with CO is markedly more important than the one detected from reduction with H₂. Furthermore, the oxygen storage capacity (OSC) for sulfated samples is higher than the one for sulfate-free samples. This is tentatively explained by the partial replacement of oxygen by sulfur atoms in the compound lattice.

Keywords: Three way catalysts; Oxygen storage capacity; Ceria–zirconia; Platinum; Sulfate; Sulfur dioxide; Carbon monoxide; IR spectroscopy; Thermogravimetry

Highly stable ytterbium promoted Ni/γ-Al₂O₃ catalysts for carbon dioxide reforming of methane by Mohamad Hassan Amin; Kshudiram Mantri; Jarrod Newnham; James Tardio; Suresh K. Bhargava (pp. 217-226).

The addition of Yb to Ni(20wt%)/γ-Al₂O₃ (prepared via a sol–gel method) led to significant increases in activity and stability in this material for catalysing carbon dioxide reforming of methane. The improved properties of the Ni(20wt%)-Yb(2wt%)/γ-Al₂O₃ catalyst were most likely due predominantly to the Yb facilitating the formation of nickel particles with a lower average diameter. The aforementioned catalyst also experienced significantly lower carbon deposition compared to the un-doped catalyst.Display Omitted► Highly active and stable Yb promoted Ni/γ-Al₂O₃ sol–gel prepared catalysts for CO₂ reforming of CH₄ at 700°C. ► Optimal Yb doping for catalysts investigated was 1–2wt%. ► Average Ni particle diameter was lowest in catalyst doped with 2wt% Yb. ► Catalyst with 2wt% Yb experienced significantly lower carbon deposition compared to un-doped catalyst.The influence of Yb on Ni(20wt%)/γ-Al₂O₃ catalysts (prepared via a sol–gel method) for use in the dry reforming of methane was investigated. It was found that the addition of low quantities of Yb (1–2wt%) led to significant increases in catalytic activity and catalyst stability, and the production of H₂ and CO at a ratio close to unity (∼0.95). Higher levels of Yb doping (3–8wt%) did not achieve similar increases in activity as those observed in the lower level doped catalysts. Based on characterisation studies conducted on the catalysts before and after testing it was found that the catalyst with a low level of Yb (2wt%) had the smallest average Ni particle size, narrowest particle size distribution and highest ease of reducibility (based on Temperature Programmed Reduction analysis). Analysis of the catalysts after testing showed that the catalyst with 2wt% Yb also experienced the lowest level of carbon deposition and contained a high degree of graphitised carbon. The results obtained indicate that doping of Ni-Al₂O₃ catalysts with a select amount of Yb can give rise to a catalyst with excellent properties for use in the dry reforming of methane and that Yb can have a significant role in controlling the size/mobility of Ni nanoparticles produced via reduction of NiO.

Keywords: CO; ₂; reforming of methane; Yb/Ni/γ-Al; ₂; O; ₃; Syngas

Two-step sequence for synthesis of efficient PtSn@Rh/C catalyst for oxidizing ethanol and intermediate products by Shuqin Song; Chaoxiong He; Jinchao Liu; Yi Wang; Angeliki Brouzgou; Panagiotis Tsiakaras (pp. 227-233).

The PtSn@Rh/C, prepared through the two-step sequence by the modified pulse microwave assisted polyol method, followed by the heat treatment in a reductive atmosphere, exhibited significantly enhanced activity towards the electrooxidation of ethanol as well as its oxidation intermediate products (acetaldehyde and acetic acid) compared to the untreated PtSn@Rh/C and PtSnRh/C by the one-step method.Display Omitted► PtSn@Rh/C was prepared via a two step sequence synthesis, followed by heat treatment. ► PtSn@Rh/C was tested for ethanol and its intermediated products electro-oxidation. ► PtSn@Rh/C exhibits enhanced activity towards ethanol electro-oxidation. ► PtSn@Rh/C exhibits enhanced activity towards ethanol's intermediates oxidation.PtSn@Rh/C-HT catalysts were designed and synthesized by a two-step sequence synthesis: Rh was firstly deposited on the carbon support and then PtSn through microwave assisted polyol method, followed by the heat treatment (HT) in a reductive atmosphere. This well-designed process provided PtSn@Rh/C-HT with a desirable electrocatalytic activity towards the electrooxidation of ethanol as well as its intermediate products. Especially, for the acetic acid electrooxidation, PtSn@Rh/C-HT behaved quite different from Pt/C, PtSn/C, PtSn@Rh/C without heat-treatment, and PtSnRh/C fabricated through one-step method, without the characteristic peaks for hydrogen adsorption–desorption but significant oxidation current of acetic acid. This gives a platform for taking full advantage of the joint synergistic effect among Pt, Sn and Rh for direct ethanol fuel cell applications.

Keywords: PtSn@Rh/C; Ethanol electrooxidation; Acetaldehyde electrooxidation; Acetic acid electrooxidation

Enhanced emissions of NH₃, N₂O and H₂ from a Pd-only TWC and supported Pd model catalysts: Light-off and sulfur level studies by Isidro Mejía-Centeno; Salvador Castillo; Gustavo A. Fuentes (pp. 234-240).

The presence of SO₂, or sulfur level in gasoline, seems to have a dual effect at high temperature, 500°C. It suppresses selectively the reaction path leading to NH₃, but N₂O is promoted.Display Omitted► Pd-only converters catalyze the formation of NH₃, N₂O and H₂ from engine exhaust. ► NO reacts with CO and H₂ to produce N₂O below 320°C. ► NH₃ is formed by reduction of NO with H₂ between 200 and 600°C. ► H₂ is generated over the catalyst by SR and WGS.In this work we study the formation of NH₃, N₂O and H₂ side products during operation of three-way catalytic converters (TWC) in a simulated engine exhaust. We used a commercial Pd-only TWC and supported Pd model catalysts in light-off and during constant temperature tests under rich conditions. N₂O is observed primarily during light-off and its low temperature formation (110–320°C) proceeds via reduction of NO by CO when O₂ is present, or by H₂ in its absence. We detected also N₂O formation at 500°C that has not been reported previously, proceeding via reduction with CO.NH₃ is formed in the 200–600°C range via reduction of NO by H₂. The H₂ required to produce NH₃ is generated via steam reforming and water gas-shift reactions over the catalysts. On a molar basis, the H₂ emission is about five-fold higher than that of NH₃ during cold start of TWC.We determined the effect of SO₂ level during constant temperature experiments at 500°C, extending the work of Gandhi and Shelef . In CeO₂-containing catalysts the interaction with SO₂ favors the production of N₂O, but lowers that of NH₃, apparently by suppressing selectively the reaction path leading to H₂ needed for the reaction.Our study suggests that the use of low and ultra-low sulfur gasoline by cars equipped with TWC lowers the emission of N₂O to the atmosphere during high temperature operation but enhances the production of NH₃ and H₂. This is a matter of concern because NH₃ is involved in the formation of nano, fine and ultra fine inorganic particles in the atmosphere.

Keywords: Ammonia; Nitrous oxide; Hydrogen; Palladium; TWC; Greenhouse gases; Sulfur level in fuel

Protection of palladium catalysts for hydrodechlorination of chlorinated organic compounds in wastewaters by Rotem Navon; Shay Eldad; Katrin Mackenzie; Frank-Dieter Kopinke (pp. 241-247).

Display Omitted► Protection for Pd is effective against ionic catalyst poisons and macromolecules. ► PDMS coats allow several catalytic cycles but the silicone slowly ages. ► Fast and complete release of chloride from coated catalyst is a crucial step. ► Hydrodechlorination proceeds in dry organic solvents such as n-hexane. ► The protection strategy is a big step forwards for the utilization of Pd catalysts.Palladium is an efficient catalyst for hydrodechlorination (HDC) of aliphatic and aromatic chlorinated organic compounds in water. However, its applicability in water treatment processes is limited because of its sensitivity to catalyst poisons. In the present study, Pd/Al₂O₃ was modified by various silicone-based fillings and coatings. The modified catalysts proved to be active in the HDC of chlorobenzene with A_Pd=35–65Lg_Pd⁻¹min⁻¹ vs. 570Lg_Pd⁻¹min⁻¹ for the unprotected catalyst. It was insusceptible against sulphite as a model catalyst-deactivating ionic water constituent. However, under HDC conditions the silicone appeared to be degraded, becoming gradually permeable for sulphite. Hydrolysis of the silicone polymers, initiated and promoted by the HDC product HCl, is assumed to be responsible for the polymer ageing. Release of chloride from the coated catalyst into the bulk water phase has been revealed as a crucial step in this concept of hydrophobic catalyst protection. It could be shown that with Pd/Al₂O₃, HDC also proceeds in dry organic solvents such as n-hexane at significant reaction rates ( A_Pd=18–28Lg_Pd⁻¹min⁻¹).

Keywords: Hydrodechlorination; Palladium; Silicone; Catalyst poisoning; Catalyst protection; Catalyst coating

Pd and PdAu catalysts supported over 3-MPTES grafted HMS used in the HDS of thiophene by Valeria La Parola; Maria Luisa Testa; Anna Maria Venezia (pp. 248-255).

Display Omitted►SH grafting of HMS increases the surface dispersion of supported PdAu catalysts. ►SH grafting of HMS enhances the HDS activity of the Pd and PdAu supported catalysts. ► The PdAu showed a larger promoting effect as compared to Pd supported catalysts. ► The promotion of the catalytic performance is related to theSH loading.Palladium and bimetallic palladium-gold catalysts were supported over mesoporous silica HMS grafted with variable amount of mercaptopropyl groups corresponding to different molar ratio of theSH group over the metal, moles_SH/moles_metal=2, 4, 7, 9. The obtained catalysts, characterized by XRD and XPS techniques were tested in the hydrodesulphurization (HDS) reaction of thiophene. Generally speaking, all the bimetallic catalysts were more active as compared to the monometallic ones. The support modification affected the structure of the fresh (calcined) and reduced catalysts. Supporting the metals over the bare HMS, through deposition–precipitation with urea, produced a drastic decrease of the surface area at variance with the catalysts supported over the functionalized HMS which maintained fairly high surface areas. According to the XRD, the introduction of theSH groups contributed to the better dispersion of the PdO and metallic gold in the calcined samples. Upon hydrogen treatment the supported metals transformed into small particles of gold enriched alloy leading to high activity and lower catalyst deactivation. The promotion of the catalytic behaviour increased with the increase of theSH loading up to a molar ratio, moles_SH/moles_metal=7. Above this value, the beneficial effect started diminishing. Based on the XPS and the XRD results, the catalytic behaviour was correlated with the structure and surface composition of the supported species, governed by the interaction between the metals and the mercaptogroups.

Keywords: HMS; Mercaptopropyl; PdAu catalysts; HDS; Thiophene

Selective catalytic reduction of NO_x with methanol over supported silver catalysts by Marika Männikkö; Magnus Skoglundh; Hanna Härelind Ingelsten (pp. 256-266).

.Display Omitted► The effect of catalyst composition on the lean NO_x reduction during methanol-SCR. ► Silver supported on alumina and ZSM-5. ► Ag-Al₂O₃ (sol–gel) show promising results under methanol-SCR conditions. ► The support material, the Ag loading and the nature of the Ag sites are essential. ► Improved activity over Ag-Al₂O₃ with hydrogen addition and higher C/N molar ratio.Methanol is a potential renewable fuel for the transport sector and is thus interesting to study as reducing agent for NO_x in hydrocarbon assisted selective catalytic reduction (HC-SCR). The effect of catalyst composition on the lean NO_x reduction during methanol-SCR conditions was investigated. In particular silver supported on alumina and ZSM-5 were in focus and parameters that can improve the NO_x reduction performance, i.e. the C/N molar ratio and the addition of hydrogen, were specifically studied. Five catalysts were prepared (H-ZSM-5, Ag/H-ZSM-5, Pd/Ag/H-ZSM-5, γ-Al₂O₃ and Ag-Al₂O₃) and compared in flow reactor experiments. The Ag-Al₂O₃ (2wt% Ag, sol–gel) sample was found to give higher NO_x reduction compared to the other tested samples, where important factors are suggested to be the support material, the preparation method and the Ag loading. The NO_x reduction over Ag-Al₂O₃ with methanol is proposed to proceed by adsorbed nitrates or nitrites (or gas phase NO₂) reacting with adsorbed acetate or formaldehyde like species forming adsorbed RNO₂ or RONO, with subsequent conversion intoNCO,CN, RNH₂ or NH₃, with final desorption of N₂ and CO_x (or HCHO). The addition of hydrogen and an increase of the supplied methanol concentration resulted in an increased NO_x reduction mainly over the Ag-Al₂O₃ sample, where the addition of hydrogen also extended the active temperature interval towards lower temperatures. Another effect of the addition of hydrogen was formation of more oxidized carbon containing reaction products. The Ag-Al₂O₃ catalyst prepared by the sol–gel method, including freeze-drying of the formed gel, is concluded to be the most promising candidate of the tested catalysts for methanol-SCR.

Keywords: Silver/alumina; Silver/ZSM-5; Methanol-SCR; Lean NO; _x; reduction; Hydrogen

Hierarchical P/YPO₄ microsphere for photocatalytic hydrogen production from water under visible light irradiation by Feng Wang; Chuanhao Li; Yecheng Li; Jimmy C. Yu (pp. 267-272).

Display Omitted► Hierarchical P/YPO₄ hollow microspheres are prepared by reacting red P with YCl₃. ► The product consists of crystalline YPO₄ nanosheets and amorphous red phosphorus. ► The composite shows high activity for photocatalytic hydrogen formation from water.Hierarchical P/YPO₄ hollow microspheres are prepared by the reaction between amorphous red P and YCl₃ aqueous solution via a hydrothermal method. The final product consists of crystalline YPO₄ nanosheets and amorphous red phosphorus. Photocatalytic hydrogen formation measurements indicate that the P/YPO₄ composites exhibit higher activity than the individual components. The composite with 53wt% YPO₄ is up to 6 times more active than red phosphorus under visible light irradiation. The formation mechanism of hierarchical microspheres and the enhanced photocatalytic activity are discussed.

Keywords: Hydrogen production; Photocatalyst; Red phosphorus; Visible-light-driven; Yttrium phosphate

Modeling of the catalytic removal of CO and NO under lean-burn conditions: Can there be too much catalyst? by Alexei G. Makeev; Nickolai V. Peskov; Hiromichi Yanagihara (pp. 273-278).

Display Omitted► We model the NO+CO reaction under lean-burn conditions in CSTR. ► We studied the influence of the catalyst surface area on the NO and CO conversion. ► We showed that the NO conversion can decrease when a catalyst loading increases. ► The underlying kinetic mechanism was explained in details.The NO+CO+O₂ reaction under net-oxidizing conditions may demonstrate an interesting phenomenon: the conversion of NO to N₂ decreases when the amount of catalyst increases. This behavior has been observed in many experimental studies and, as a rule, it has been attributed to the structural sensitivity of the catalytic reaction. Using the classical theories of heterogeneous catalytic reactions and chemical reactors, we demonstrate that this unusual effect can be well explained by the peculiarities of the reaction mechanism and kinetics of competing reactions.

Keywords: Modeling; Nitrogen monoxide; Carbon monoxide; Surface reaction mechanism; NO conversion maximum; Lean-burn conditions; Effect of catalyst loading

NO_x storage and reduction over flame-made M/MgAl₂O₄ (M=Pt, Pd, and Rh): A comparative study by Sounak Roy; Niels van Vegten; Nobutaka Maeda; Alfons Baiker (pp. 279-286).

M/MgAl₂O₄ (1wt% M: Pt, Pd, or Rh) catalysts were prepared by single step flame spray pyrolysis. The thermal stability of the stored NO_x and the storage–reduction performance during lean-rich cycling with different reductants, H₂, CO and C₃H₆, was investigated by means of TG and time-resolved in situ DRIFTS.Display Omitted► M/MgAl₂O₄ catalysts (M=Pt, Pd or Rh) were prepared by flame spray pyrolysis. ► NSR performance of the catalysts decreased according to Rh>Pt>Pd. ► NO oxidation activity decreased according to Pt>Rh>Pd. ► Stability of NO_x species adsorbed decreased in the order Pd>Pt>Rh. ► NO_x reduction activity decreased according to Rh>Pd>Pt.Various NO_x storage–reduction (NSR) catalysts with 1wt% noble metal loading (Pt, Pd, or Rh) dispersed on MgAl₂O₄ have been synthesized by single step flame spray pyrolysis. The as-prepared powders consisting of nonporous nanoparticles were characterized by X-ray diffraction, scanning transmission electron microscopy, nitrogen adsorption–desorption, CO chemisorption and thermogravimetric methods. Different reduction agents were applied in the fuel rich cycles: H₂, CO or C₃H₆. Processes occurring during fuel rich and lean cycles were analyzed in detail by means of time-resolved diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and thermogravimetry combined with mass spectroscopy. With H₂ as reductant, Pt/MgAl₂O₄ showed the best performance at short regeneration time (<50s), followed by Rh/MgAl₂O₄ and Pd/MgAl₂O₄. However, if CO or C₃H₆ were used as reductant, Rh/MgAl₂O₄ outperformed both other catalysts, especially at longer regeneration times (>50s). NO_x storage on these catalysts was mainly restricted to surface species, although bulk nitrate species were identified by DRIFTS as well. The latter were not completely reduced under the experimental conditions used.

Keywords: NO; _x; storage and reduction; Platinum; Palladium; Rhodium; MgAl; ₂; O; ₄; Spinel; Dynamic cycling behavior; Time-resolved IR spectroscopy

In situ investigation of Diesel soot combustion over an AgMnO_x catalyst by N. Guilhaume; B. Bassou; G. Bergeret; D. Bianchi; F. Bosselet; A. Desmartin-Chomel; B. Jouguet; C. Mirodatos (pp. 287-296).

.Display Omitted► An AgMnO_x oxide catalyst shows high activity for low temperature soot oxidation. ► Soot combustion under¹⁸O₂ forms preferentially C¹⁶O₂ and C¹⁶O. ► The reaction follows a redox mechanism. ► Lattice oxygen transfer to the soot is responsible for ignition. ► Ag promotes Mn³⁺ reduction and Mn²⁺ oxidation.An AgMnO_x catalyst (3.5wt.% Ag) incorporating silver ions in a Mn₂O₃ phase exhibits high performances for soot oxidation below 300°C. Its structural and redox properties have been investigated under reaction conditions using in situ XRD and DTA-TGA measurements. The catalyst appears unmodified during soot combustion experiments under oxygen, but in the absence of oxygen the soot is stoichiometrically oxidised by lattice oxygen leading to catalyst bulk reduction according to the steps Mn₂O₃→Mn₃O₄→MnO.The isotopic reaction product composition (C¹⁶O₂, C¹⁸O¹⁶O, C¹⁶O₂, C¹⁶O and C¹⁸O) obtained during soot combustion experiments under¹⁸O₂ reveals that the reaction follows a redox mechanism, in which the transfer of lattice oxygen from the catalyst to the soot is responsible for the soot ignition at low temperature.

Keywords: Diesel soot; Soot combustion; Mechanism; Ag–Mn mixed oxide; In-situ XRD; Oxygen isotopic exchange

Dry regenerable CuO/γ-Al₂O₃ catalyst for simultaneous removal of SOx and NOx from flue gas by Fatemeh Rahmaninejad; Vasudeo S. Gavaskar; Javad Abbasian (pp. 297-303).

Display Omitted► Novel regenerable CuO/γ-Al₂O₃ sorbent/catalyst were evaluated for NOx removal from flue gas. ► The CuO/γ-Al₂O₃ catalyst was shown to be capable of removing close to 100% of NOx in both oxidized (regenerated), and sulfated state in fluidized bed reactor. ► The presence of steam was shown to enhance the catalytic activity. ► The catalytic activity of the sorbent/catalyst was shown to be unaffected by the cyclic process after 25 cycles.The catalytic activity of a highly reactive and attrition resistant regenerable CuO/γ-Al₂O₃ desulfurization sorbent for NOx reduction was determined in a fluidized-bed reactor. The NO conversion over the sulfated catalyst was found to be higher than that obtained over the fresh/oxidized catalyst, with the optimum temperatures for the maximum NO removal at 350°C for both catalysts. The decrease in NO conversion above the optimum temperature is attributed to the increase in the rate of the parallel NH₃ oxidation reaction. High levels of ammonia oxidation (i.e., >96%) was observed in absence of oxygen and NO with oxidized sorbent/catalyst, indicating the participation of the lattice oxygen ions in the CuO/γ-Al₂O₃ particles in the NH₃ oxidation reaction. The presence of steam enhances the catalytic activity of the catalysts providing a wider optimum temperature window, thus resulting in a more flexible operation for simultaneous SOx/NOx removal from flue gas.

Keywords: Simultaneous; SOx; NOx; Regenerable; Copper oxide; Flue gas; High temperature

Dehydrative esterification of carboxylic acids with alcohols catalyzed by diarylammonium p-dodecylbenzenesulfonates in water by Takeshi Igarashi; Daisuke Yagyu; Takeshi Naito; Yoshikuni Okumura; Tetsuo Nakajo; Yuichiro Mori; Shū Kobayashi (pp. 304-307).

Display Omitted► This work contributes a basic part toward practical use in chemical plants. ► Dodecylbenzenesulfonic acid-diarylamine salts catalyze esterification in water. ► High hydrophobicity of the catalysts can suppress their solubility in water. ► This system is applicable to the recovery of acetic acid and flow reaction system. ► This catalytic system is applicable to hydrophobic substrates in water.We have developed direct esterification reaction of carboxylic acids with alcohols catalyzed by diarylammonium salt catalysts toward the recovery of acetic acid from wastewater of chemical plants. Hydrophobicity of the catalysts could suppress their solubility in water. This esterification reaction has been applied to the recovery of acetic acid using a flow reaction system which is applicable to practical use in chemical plants. It was shown that this catalytic system was also applicable to the combination of hydrophobic substrates in water.

Keywords: Direct esterification; Ammonium salt; Water; Acetic acid; Wastewater

Influence of cerium precursors on the structure and reducibility of mesoporous CuO-CeO₂ catalysts for CO oxidation by Lei Qi; Qiang Yu; Yue Dai; Changjin Tang; Lianjun Liu; Hongliang Zhang; Fei Gao; Lin Dong; Yi Chen (pp. 308-320).

.Display Omitted► The influence of cerium precursors on mesoporous CuO-CeO₂ was investigated. ► (NH₄)₂Ce(NO₃)₆ improves catalyst texture, instead of increasing activity. ► Ce(NO₃)₃ induces more Ce³⁺ and oxygen vacancies and enhances Cu–Ce interaction. ► Ce(NO₃)₃ promotes catalyst reducibility and CO oxidation activity. ► CO oxidation activity depends on Cu–Ce synergistic effect, instead of structure.This work investigated the effects of cerium precursors [Ce(NO₃)₃ and (NH₄)₂Ce(NO₃)₆] on the structure, surface state, reducibility and CO oxidation activity of mesoporous CuO-CeO₂ catalysts. The catalysts were characterized by TG–DTA, XRD, LRS, N₂ adsorption–desorption, HRTEM, XPS, H₂-TPR and in situ FT-IR. The obtained results suggested that the precursors exerted a great influence on the properties of CuO-CeO₂ catalysts: (1) compared with the catalysts from Ce(III) precursor, the derived Ce(IV) precursor catalysts showed smaller grain size, higher BET surface area, narrower pore size distribution, whereas their reducibility and activities were not enhanced. (2) In contrast, the catalysts from Ce(III) precursor without excellent texture displayed high reducibility and activities for CO oxidation due to the high content of Ce³⁺, following the redox equilibrium of Cu²⁺+Ce³⁺↔Cu⁺+Ce⁴⁺ shifting to right to form more stable Cu⁺ species, which was the origin of synergistic effect. The synergistic effect between copper and cerium was the predominant contributor to the improved catalytic activities of CuO-CeO₂ catalysts, instead of structural properties.

Keywords: Cerium precursor; Synergistic effect; Reducibility; CuO-CeO; ₂; CO oxidation

Enhanced hydrothermal stability of high performance lean fuel combustion alumina-supported palladium catalyst modified by nickel by Ying Liu; Sheng Wang; Tianjun Sun; Diannan Gao; Chunxi Zhang; Shudong Wang (pp. 321-328).

Display Omitted► Pd/Al₂O₃ catalyst modified by nickel for methane combustion under lean-fuel condition. ► Catalyst on NiAl₂O₄ support demonstrates the most excellent hydrothermal stability. ► The methane conversion of Pd/NiAl₂O₄ was still about 96% at 823K after 3200h test. ► The least lattice mismatch between Pd and NiAl₂O₄ leads to high Pd dispersion. ► Pd/NiAl₂O₄ catalyst is an appropriate candidate for lean fuel methane combustion.The hydrothermal stability of Pd-based methane combustion catalyst was investigated under lean-fuel conditions, such as ventilation air methane. For the catalyst, the active component Pd was impregnated on Ni-modified alumina supports which were prepared by a modified method. The method was coupled with the conventional co-precipitation and hydrothermal synthesis process. A series of Pd catalysts and supports prepared, which had the Ni/Al ratios of 1:4, 1:2 and 1:1, were characterized by BET, CO-chemisorption, XRD, TPR, SEM and TEM. The relationship between active sites and supports was studied using HRTEM. In addition, the performances for lean methane combustion of all catalysts were studied. Results showed that the catalyst on well crystallized NiAl₂O₄ spinel support exhibited the superior hydrothermal stability. Methane conversion remained 96% after 3200h at 873K. Such excellent catalytic performance has been validated to relate to the stabilizing effect of support and the least lattice mismatch between NiAl₂O₄ and Pd, which contributed to high Pd dispersion.

Keywords: Ventilation air methane combustion; Palladium; NiAl; ₂; O; ₄; spinel; Lattice mismatch

Surface oxygen generated upon N₂O activation on iron containing ZSM-5 type zeolites with different elemental composition by Ayten Ates; Andreas Reitzmann; Gerrit Waters (pp. 329-339).

Display Omitted► The formation of surface oxygen depends on the certain types of iron species. ► Multinuclear iron species contributes to the surface oxygen formation. ► Bulky oxide species has only a minor impact on surface oxygen formation. ► Zeolites containing bulky iron oxide clusters also release additional oxygen. ► The Si/Al ratio of parent zeolite indirectly affects the surface oxygen formation.Various ZSM-5 zeolites with iron contents ranging from of 0.86 to 4.98 and Si/Al ratios of 11.5–140 were prepared by solid-state ion exchange with FeCl₂. The catalysts were characterised by XRD, H₂-TPR and NH₃-TPD. The formation and stability of surface oxygen over these zeolites were investigated with a transient multipulse technique combined with subsequent temperature-programmed desorption (TPD). Higher iron contents enhance the formation of surface oxygen. However, when a critical iron content is reached, larger iron oxide clusters and particles are formed and these larger clusters do not contribute significantly to surface oxygen formation. Moreover, the amount of desorbed oxygen is more than that formed from N₂O due to the additional desorption of oxygen present in the lattice of such oxide clusters. TPD studies indicate the presence of different surface oxygen species depends on both the zeolite iron content and Si/Al ratio.

Keywords: Nitrous oxide decomposition; Fe-ZSM-5; Multipulse method; Surface oxygen

Highly selective catalytic propylene glycol synthesis from alkyl lactate over copper on silica: Performance and mechanism by Mikhail N. Simonov; Pavel A. Zaikin; Irina L. Simakova (pp. 340-347).

Display Omitted► 96% selectivity to propylene glycol from alkyl lactate over Cu/SiO₂ at 1bar H₂. ► Butyl lactate enables higher selectivity due to resistance of released butanol to side transformations. ► Mechanism of alkyl lactate hydrogenolysis is proposed where propylene glycol and hydroxyacetone are in thermodynamic equilibrium. ► Cu/SiO₂ catalyst is stable for more than 200h time-on-stream.Catalytic alkyl lactate hydrogenolysis over silica-supported copper at atmospheric hydrogen pressure and temperature range 433–493K provides an eco-friendly green alternative to the petroleum-based process for propylene glycol synthesis. It was shown that catalytic activity strongly depends on copper loading and the most active catalyst contains ca. 45wt.% Cu. General peculiarities of methyl and butyl lactate hydrogenolysis were studied demonstrating that an overall reaction rate increases with reaction temperature increase but a selectivity to propylene glycol decreases due to enhanced concurrent dehydrogenation of propylene glycol to a by-product hydroxyacetone. It was found that the amount of propylene glycol formed during the reaction is determined by thermodynamic equilibrium between propylene glycol and hydroxyacetone that results in propylene glycol selectivity of 96% at full butyl lactate conversion at 453K. Overall mechanism of alkyl lactate transformation involving formation of intermediate hemiacetal over bifunctional Cu/SiO₂ catalyst was proposed.

Keywords: Hydrogenolysis; Alkyl lactate; Propylene glycol; Copper-silica

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Applied Catalysis B, Environmental (v.119-120, #)