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Applied Catalysis B, Environmental (v.94, #1-2)

Contents Continued (pp. iii).

IFC Editorial Board (pp. co2).

Editorial Board (pp. i).

Contents (pp. co4).

Immobilization of chromium complexes in zeolite Y obtained from biosorbents: Synthesis, characterization and catalytic behaviour by H. Figueiredo; B. Silva; C. Quintelas; M.M.M. Raposo; P. Parpot; A.M. Fonseca; A.E. Lewandowska; M.A. Bañares; I.C. Neves; T. Tavares (pp. 1-7).

The goal of this study is the preparation of new heterogeneous catalytic materials to be used in oxidation reactions under mild conditions through the valuation of heavy metals in wastewater. The samples used in the immobilization of chromium complexes were prepared from a dichromate solution of 100mg_CrL⁻¹. The zeolite CrNaY was prepared from a robust biosorption system consisting of a bacterial biofilm, Arthrobacter viscosus, supported on zeolite NaY. The biofilm performs the reduction of Cr(VI) to Cr(III) and this cation is retained in the zeolite by ion exchange. The immobilization of chromium complexes with heterocyclic ligands in the supercages of Y zeolite was performed by the in situ synthesis with three different ligands, 3-methoxy-6-chloropyridazine (A), 3-piperidino-6-chloropyridazine (B) and 1-(2-pyridylazo)-2-naphthol (C). A sample loaded with Cr from a liquid solution with the same initial concentration was prepared as a reference through the traditional direct ion-exchange method and coordinated with ligand (A). The resulting catalysts were fully characterized by different techniques (FTIR, XRD, TGA, SEM, Raman, cyclic voltammetric studies and chemical analysis) and the results confirmed that the Cr complexes were immobilized in supercages of NaY. Catalytic studies were performed in liquid phase for the cyclohexene oxidation, at 40°C, using tert-butyl hydroperoxide (TBHP) as the oxidizing agent. All the prepared catalysts exhibited catalytic activity for the oxidation reaction.

Keywords: NaY; Arthrobacter viscosus; Biosorbents; Cr; Heterocyclic ligands; Immobilization; Cyclohexene oxidation

Pd supported on mesoporous activated carbons with high oxidation resistance as catalysts for toluene oxidation by J. Bedia; J.M. Rosas; J. Rodríguez-Mirasol; T. Cordero (pp. 8-18).

Mesoporous activated carbons were obtained by chemical activation of kraft lignin with H₃PO₄ and used as supports for the preparation of carbon-based Pd catalysts with low palladium content (0.5%). The catalytic properties of the carbon-based Pd samples were evaluated in the catalytic oxidation of toluene. The effect that a thermal treatment at 900°C in inert atmosphere carried out before and after the Pd-deposition produced on the structure and activity of the catalysts was analyzed. The catalysts obtained show high external surface areas and mesopore volumes. The chemical activation with H₃PO₄ yielded carbon supports with a significant amount of surface phosphorus, in form of COPO₃, CPO₃ and C₃PO groups. These phosphorus groups act like physical barrier, increasing the oxidation resistance of the catalysts and avoiding the burn-off of the carbon substrate during the oxidation of the VOCs. TEM analysis confirmed the presence of well-dispersed Pd particles, with sizes between 5 and 12nm. A kinetic study of the catalytic oxidation of toluene was performed. The reaction seems to proceed through a Langmuir–Hinshelwood mechanism, whose rate-limiting step is the surface reaction between adsorbed toluene and oxygen adsorbed dissociatively, with an activation energy value of 83kJmol⁻¹. Toluene and xylene were oxidized to CO₂ and H₂O in the temperature range of 150–400°C at a space velocity of 19,000h⁻¹.

Keywords: Activated carbon; Catalytic oxidation; Palladium; VOC; Toluene

Plasma-catalytic methane conversion with carbon dioxide in dielectric barrier discharges by Jan Sentek; Krzysztof Krawczyk; Michal Młotek; Małgorzata Kalczewska; Thorsten Kroker; Torsten Kolb; Andreas Schenk; Karl-Heinz Gericke; Krzysztof Schmidt-Szałowski (pp. 19-26).

The hybrid plasma-catalytic system was tested for the mixture of methane and CO₂ conversion at the pressure of 1.2bar with the use of a dielectric barrier discharge (DBD) reactor powered at the frequency of 5.7–6kHz. Three kinds of catalytic packing were examined: alumina ceramic carrier (Al₂O₃) and two catalysts, i.e. Ag/Al₂O₃ and Pd/Al₂O₃. The effects of temperature (120–290°C), [CO₂]:[CH₄] molar ratio in the inlet gas mixtures (CH₄+CO₂+Ar), gas flow rate, and specific energy on the conversion were studied. Hydrogen, carbon oxide, hydrocarbons (ethane, ethylene+acetylene fraction, propane, propylene, n-butane, and i-butane), and alcohols (methanol and ethanol) were identified in the outlet gas. Among the organic gaseous products, ethane was dominant over the entire parameter range under examination. Non-volatile products (carbon, macromolecular substances) formed a visible deposit on the quartz dielectric barrier and metal electrode surfaces. With the Pd/Al₂O₃ catalyst, the overall methane conversion was 30–50% and the methane conversion to C2–C4 hydrocarbons reached 22%.

Keywords: Methane conversion; Carbon dioxide; Barrier discharge; Catalyst

Catalytic combustion of methane on nano-structured perovskite-type oxides fabricated by ultrasonic spray combustion by Xun Wei; Paul Hug; Renato Figi; Matthias Trottmann; Anke Weidenkaff; Davide Ferri (pp. 27-37).

The synthesis of perovskite-type oxides using ultrasonic spray combustion (USC) was investigated by adjusting the composition of the precursor solution and the temperature of synthesis and calcination. LaMnO₃ was chosen as model perovskite to systematically analyze the effect of USC operating parameters. XRD, IR spectroscopy, TG-TPD, SEM, TEM and BET were used to characterize the samples with respect to phase composition, thermal stability, morphology and surface area. The catalytic properties were evaluated with respect to methane combustion as such materials are potential catalysts in the control of exhaust gases from mobile and stationary sources. Addition of citric acid to the precursor solution and calcination in air appeared to be the crucial parameters to produce spherical hollow particles composed of nano-sized LaMnO₃ crystallites (down to 30nm) with high catalytic activity and durability. Calcination was required in order to remove uncombusted precursors and to improve both the crystallinity of the materials and their catalytic activity. LaFeO₃, LaCoO₃ and La(M,Pd)O₃ (M=Mn, Fe) with pure perovskite-phase were synthesized in a single step under the optimal conditions selected for LaMnO₃. Though the order of catalytic activity within the two series of samples (with and without Pd) agreed with reported trends, the production of each single perovskite composition by USC may require further optimization around these synthesis conditions. We demonstrate that USC is a simple, versatile and reliable method with potential application in the one-step synthesis of heterogeneous catalysts.

Keywords: Ultrasonic spray combustion; Perovskites; Methane combustion; Hollow particles; Palladium

One-step non-hydrolytic sol–gel preparation of efficient V₂O₅-TiO₂ catalysts for VOC total oxidation by Damien P. Debecker; Karim Bouchmella; Romain Delaigle; Pierre Eloy; Claude Poleunis; Patrick Bertrand; Eric M. Gaigneaux; P. Hubert Mutin (pp. 38-45).

Vanadia-titania catalysts are highly regarded for the control of industrial and domestic gas effluents. They are particularly used for the abatement of volatile organic compounds and for the removal of aromatic, polyaromatic and polychlorinated air pollutants like furans and dioxins. Here, mixed oxide catalysts are formed by non-hydrolytic condensation of chloride precursors with diisopropyl ether in non-aqueous medium. Calcination was applied to provoke the migration of the vanadium oxide toward the surface of the anatase particles, leading to well-spread vanadia species. The materials are made of mesoporous spherical particles of a few microns, themselves constituted by the aggregation of 10–25nm sized particles. Their chemical composition is precisely controlled. The samples are characterized by ICP-AES, N₂-physisorption, XRD, XPS, SEM and TOF-SIMS. Their performances as total oxidation catalyst are evaluated in the deep oxidation of benzene, chosen as a model atmospheric pollutant. The activity of the materials compares well with that of catalysts prepared by classical wet impregnation. Along with the V surface concentration, the environment in which V surface species are located is identified as a key parameter. The superior activity of polymeric species as compared to isolated ones is shown.

Keywords: Alkoxide; PCDD; PCDF; Air pollution; SCR; Nonhydrolytic

Complete n-hexane oxidation over supported Mn–Co catalysts by S. Todorova; H. Kolev; J.P. Holgado; G. Kadinov; Ch. Bonev; R. Pereñíguez; A. Caballero (pp. 46-54).

Two series of Co–Mn samples were prepared by impregnation of silica with aqueous solutions of Co(NO₃)₂·6H₂O and/or Mn(NO₃)₂·6H₂O. Cobalt oxide was the predominant phase in one of the series and manganese was used as the promoter. The major component in the second series was manganese oxide and Co was the promoter. The prepared samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) and tested in the reaction of complete n-hexane oxidation. The catalytic activity of both single component cobalt and manganese samples was similar, however, a combination between the two elements changed significantly the activity and this depended on the method of preparation. Catalysts prepared by a common solution of Co- and Mn nitrates manifested a considerable increase in activity as a result of very low crystallinity of the supported metal oxide phases, partial enrichment of the surface with cobalt and uniform distribution of oxide agglomerates on the support.

Keywords: Complete; n; -hexane oxidation; Supported Co–Mn oxide catalysts

Dechlorination of chloroacetic acids by Pd/Fe nanoparticles: Effect of drying method on metallic activity and the parameter optimization by Xiangyu Wang; Ping Ning; Huiling Liu; Jun Ma (pp. 55-63).

Two kinds of dry Pd/Fe nanoparticles (Pd/Fe-1 and Pd/Fe-2) were obtained by drying the laboratory synthesized wet Pd/Fe nanoparticles with direct oven drying method and solvent replacement oven drying method, respectively. A comparison was made between the two drying methods, concerning the effects of the washing reagents used during the drying process on the physicochemical properties and the activities of Pd/Fe nanoparticles for catalytic dechlorination of chloroacetic acids. Pd/Fe nanoparticles prepared by impregnation of iron nanoparticles with an aqueous solution of potassium hexachloropalladate were washed with different reagents (deionized water and organic solvents), followed by vacuum drying in an oven at 100°C. The prepared dry Pd/Fe-1 and Pd/Fe-2 nanoparticles were characterized in terms of specific surface area (BET-N₂), morphology (SEM), surface elemental distribution (EDS), and particle size (TEM). The catalytic activities of Pd/Fe-1 and Pd/Fe-2 nanoparticles were evaluated via dechlorination reaction of chloroacetic acids including trichloroacetic acid (TCAA), dichloroacetic acid (DCAA), and monochloroacetic acid (MCAA). The removal efficiencies of chloroacetic acids by Pd/Fe-2 were about 58.5–22.7% greater than that achieved by Pd/Fe-1. The optimal Pd content, the amount of metal loading, and the initial pH value of reaction system for higher removal efficiency of chloroacetic acids were determined. The variation of pH value, dechlorination pathway and kinetics of chloroacetic acids were also investigated. The removal efficiencies of chloroacetic acids followed the order of TCAA>DCAA>MCAA with observed reaction rate constant ( k_obs) values of 1.113×10⁻¹, 1.278×10⁻², and 1.900×10⁻³min⁻¹, respectively.

Keywords: Pd/Fe nanoparticles; Drying method; Chloroacetic acid; Catalytic dechlorination; Metallic activity

Theoretical elucidation of acetylating glycerol with acetic acid and acetic anhydride by Xiaoyuan Liao; Yulei Zhu; Sheng-Guang Wang; Hongmei Chen; Yongwang Li (pp. 64-70).

Density functional theory calculations on level of B3LYP functional and 6-31G** basis set are carried out on glycerol esterification reactions. The most stable structures of the reactants, intermediates and products are located by considering a large amount of conformers. The thermodynamics is discussed in terms of the calculated reaction Gibbs free energy. The glycerol esterification with acetic acid is found to be thermodynamically resisted, while its esterification with acetic anhydride is preferable with significantly exothermal property. This agrees well with experiments. The proposed process art has been experimentally and theoretically proved to be with low production costs and high head product selectivity.

Keywords: Glycerol; Esterification; Theoretical study; Acetic acid; Isomers

The poisoning effect of Na⁺ and Ca²⁺ ions doped on the V₂O₅/TiO₂ catalysts for selective catalytic reduction of NO by NH₃ by Fushun Tang; Bolian Xu; Haihua Shi; Jinheng Qiu; Yining Fan (pp. 71-76).

Deactivation of the supported V₂O₅/TiO₂ catalysts due to deposition of alkali and alkaline earth metal salts in fly ashes is one of the most important problems in the selective catalytic reduction (SCR) of NO_x by NH₃. In this work, the poisoning effect of Na⁺ and Ca²⁺ ions doped on the V₂O₅/TiO₂ catalysts for selective catalytic reduction of NO by NH₃ has been studied. It has been shown that the Na⁺ and Ca²⁺ ions doped can poison the V₂O₅/TiO₂ catalyst and the Na⁺ ions exhibit greater poisoning effect than Ca²⁺ ions. The NO rate constant k on the Na⁺-V₂O₅/TiO₂ catalyst decreased very sharply from 97.1 to 35.0cm³g⁻¹s⁻¹ with increasing Na/V molar ratio from 0.00 to 0.20. In comparison, k on the Ca²⁺-V₂O₅/TiO₂ catalyst remained almost unchanged when Ca/V molar ratio was below 0.05. Further increasing Ca/V molar ratio to 0.20 resulted in an obvious decrease of k from 101.8 to 46.3cm³g⁻¹s⁻¹. It was suggested that Na⁺ ions combined strongly with dispersed vanadia species, neutralized the Brønsted acid sites and reduced their reducibility. In comparison, Ca²⁺ ions slightly affected the Brønsted acid sites of catalyst. Besides, the dispersed vanadia species on the Ca²⁺-V₂O₅/TiO₂ catalyst had higher reducibility than Na⁺-V₂O₅/TiO₂ catalyst. The different poisoning effects of Na⁺ and Ca²⁺ ions doped on the V₂O₅/TiO₂ catalyst were correlated not only to the surface acidity but also to the reducibility of catalyst.

Keywords: V; ₂; O; ₅; /TiO; ₂; Alkaline metal ions; Surface acidity; Reducibility; SCR

Elucidation of structure–activity relationships of model three way catalysts for the combustion of methane by M. Santhosh Kumar; A. Eyssler; P. Hug; N. van Vegten; A. Baiker; A. Weidenkaff; D. Ferri (pp. 77-84).

The combustion of methane on model three way catalysts (TWC) Pd/CeZrO₂ and Pd/LaFeO₃ (2wt.% Pd) was studied under lean conditions in the temperature range between ca. 200 and 800°C to investigate the catalytic performance at and after high temperatures. The catalysts were prepared by incipient wetness impregnation and the nature and distribution of palladium species was characterized by N₂-physisorption, X-ray diffraction (XRD), visible Raman spectroscopy, X-ray absorption spectroscopy (XANES and EXAFS), H₂-temperature programmed reduction (H₂-TPR), CO adsorption followed by diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS) and CO chemisorption. The behaviour of Pd during the combustion was monitored by in situ XANES spectroscopy. The characterization results indicate that the dispersion of Pd is higher in Pd/CeZrO₂ than in Pd/LaFeO₃. The catalytic data reveal that Pd/CeZrO₂ is more active and stable compared to Pd/LaFeO₃ in the whole studied temperature range. This is also true even after subjecting the catalysts to reaction at ≥800°C as evidenced by the extent of hysteresis observed in the conversion profiles. In situ XANES studies indicate that palladium had been in the oxidized state when the catalysts showed the best combustion performance. The studies also indicate that a fraction of PdO_x had been reduced when the hysteresis was observed in the conversion profiles (while cooling between ca. 680 and 560°C) implying that the PdO_x species are the active sites, at least at T≤700°C.

Keywords: Methane combustion; Model three way catalysts; Pd/CeZrO; ₂; Pd/LaFeO; ₃; In situ XANES; Active sites

Effect of ceria nanoparticles into the Pt/C catalyst as cathode material on the electrocatalytic activity and durability for low-temperature fuel cell by Dong-Ha Lim; Weon-Doo Lee; Dong-Hyeok Choi; Ho-In Lee (pp. 85-96).

An effective method is developed for preparing highly dispersed CeO₂ nanoparticles on a Pt/C catalyst synthesized by a continuous two-step process as a cathode material in low-temperature fuel cell. The XRD patterns of the 20Pt–10CeO₂/C catalyst reveal that both crystalline Pt and CeO₂ phases coexist. The HR-TEM images show that Pt and CeO₂ nanoparticles have average particle sizes of approximately 3.4nm and 4.2nm, respectively, with quite a narrow distribution between 3nm and 5nm. Based on the analysis of the polarization curves for the ORR, the optimum proportion of CeO₂ into the 20Pt/C catalyst is 10wt%. In the ORR and single cell tests, the 20Pt–10CeO₂/C catalyst shows higher performance than the commercial 20Pt/C catalyst, owing to the oxygen storage capacity of CeO₂ and its ability to exchange oxygen rapidly with oxygen in the buffer. In the accelerated stability tests, the 20Pt–10CeO₂/C catalyst has a better durability compared to the commercial 20Pt/C catalyst due to the existence of CeO₂, which prevents the agglomeration and dissolution of Pt nanoparticles on the carbon support, extending the life of the catalyst.

Keywords: Continuous two-step process; Nano-sized metal oxide; Pt–CeO; ₂; /C electrocatalyst; Oxygen reduction reaction; Accelerated durability; Low-temperature fuel cell

The influence of surface fluorination in the photocatalytic behaviour of TiO₂ aqueous dispersions: An analysis in the light of the direct–indirect kinetic model by J.F. Montoya; P. Salvador (pp. 97-107).

TiO₂ surface fluorination is known to produce an enhancement of the photocatalytic oxidation rate of some organic compounds such as phenol, acid orange, azo dye Acid Red 1 and benzoic acid, while leads to a clear decrease of the photooxidation quantum yield of other compounds like formic acid, and dichloroacetate. Here we show that these differences in behaviour cannot be explained in the framework of the classical “Langmuir–Hinshelwood” (L–H) kinetic model, although they are compatible with the predictions of the alternative, recently developed “Direct–Indirect”(D–I) model . For weak electronic interaction of the TiO₂ surface with dissolved substrate species, as it is for instance the case for phenol, the D–I model predicts that photooxidation takes place mainly via an interfacial, indirect transfer (IT) mechanism involving inelastic trapping of valence band free holes by terminal, twofold coordinated oxygen ions, and further adiabatic transfer to dissolved substrate species. On the basis of open-circuit voltage measurements, the origin of the photooxidation quantum yield increase observed in these cases when the TiO₂ surface becomes fluorinated is attributed to the partial substitution of water molecules adsorbed on terminal Ti sites by fluoride ions, leading to: (1) an interfacial decrease of the electron-hole recombination rate as the surface concentration of recombination centres associated with terminal Ti sites diminishes; (2) an increase of the IT rate of surface trapped holes to reduced dissolved species, because of the upward shift experimented by the semiconductor energy levels with respect to filled electrolyte energy levels. In contrast, for strong electronic interaction of substrate species with the naked TiO₂ surface, as it is for instance the case of formate ions at low enough pH, photooxidation mainly take place via an interfacial, direct transfer (DT) mechanism, involving inelastic trapping of valence band free holes by specifically adsorbed substrate species. The photooxidation quantum yield decrease observed in this case is explained to be due to a diminution of the density of TiO₂ surface sites active for adsorption of formate ions. The enhanced photogeneration of free OH_S radicals and/or photooxidation rate of water molecules in the liquid phase with free VB holes, assumed by some authors as the origin of the observed photooxidation quantum yield increase at the fluorinated TiO₂ surface, should be disregarded as far as both processes appears to be thermodynamically and kinetically hindered.

Keywords: Photocatalysis; Titanium dioxide; Surface fluorination; Interfacial hole transfer modelling

Regeneration of CuO-ZnO-Al₂O₃/γ-Al₂O₃ catalyst in the direct synthesis of dimethyl ether by Irene Sierra; Javier Ereña; Andrés T. Aguayo; José M. Arandes; Javier Bilbao (pp. 108-116).

This paper deals with the regeneration of a CuO-ZnO-Al₂O₃/γ-Al₂O₃ catalyst used in the direct synthesis of dimethyl ether. When coke combustion (subsequent to aging treatment) is performed in a thermobalance, two coke fractions with different combustion kinetics are identified. One coke fraction, deposited on the metallic sites and whose combustion is activated by these sites, has a kinetic constant of combustion 7–26 times higher than that corresponding to the coke located at the Al₂O₃ support. Uninterrupted operation is feasible in reaction–regeneration cycles in a fixed bed reactor as long as the reaction and regeneration steps are carried out at 325°C, which are limiting conditions in order to avoid irreversible deactivation by sintering of the metallic function. The regeneration with O₂ diluted with He (5% of O₂) allows the complete combustion of coke. Under conditions of partial coke combustion it is observed that the removal of the fraction deposited on the metal makes it possible to recover the initial activity of the catalyst, which subsequently undergoes fast deactivation.

Keywords: Dimethyl ether; Syngas; Coke; Catalyst deactivation; Regeneration

Supported gold catalysts for the decomposition of VOC: Total oxidation of propene in low concentration as model reaction by Laurent Delannoy; Katia Fajerwerg; Pandian Lakshmanan; Claude Potvin; Christophe Méthivier; Catherine Louis (pp. 117-124).

Supported gold catalysts prepared by deposition–precipitation with urea were studied in the reaction of oxidation of propene in low concentration in a large excess of oxygen, so as to mimic the conditions of catalytic decomposition of a volatile organic compound of hydrocarbon-type (1200ppm C₃H₆, 9% O₂ in He). Several parameters were investigated: the nature of the oxide support (alumina, titania, ceria), the gold loading, the conditions of catalyst activation (oxygen or hydrogen). Titania and alumina alone did not show any conversion in C₃H₆ oxidation up to 500°C, but when gold was added (1wt%), active catalysts were obtained with a higher activity for titania than for alumina. Ceria was the only support showing activity, and gold on ceria (1wt%) led to the most active catalyst. For the Au/CeO₂ system, activation under H₂ at 300°C leads to more active catalysts than activation in O₂/He at 500°C, especially for gold loadings lower than 1wt%. XPS and CO oxidation performed at RT showed that gold on CeO₂ was fully reduced to Au⁰ after activation under H₂ whatever the gold loading. In contrast, after calcination, most of the gold remained under the initial Au^III state for the low loaded samples (≤1wt%) whereas part of it was reduced for the 4wt% Au/CeO₂. Thus, ceria seems to be able to stabilise gold as Au^III up to a limited loading. Change in the gold oxidation state was detected for the calcined Au/CeO₂ (1wt%) during C₃H₆ oxidation performed at increasing temperature, using CO oxidation and DRIFTS combined to CO adsorption. Indeed, gold, initially Au^III, starts reducing at 100°C to form metallic gold Au⁰, which was the active species for the reaction. Above 300°C, when 100% conversion was achieved, reoxidation of metallic gold species was observed.

Keywords: Gold catalysts; Ceria; Titania; Alumina; Total oxidation; VOC decomposition; Propene oxidation; CO oxidation; Gold oxidation state; Deposition–precipitation with urea; DRIFTS; XPS

Auto-thermal and dry reforming of landfill gas over a Rh/γAl₂O₃ monolith catalyst by McKenzie P. Kohn; Marco J. Castaldi; Robert J. Farrauto (pp. 125-133).

Auto-thermal and dry reforming of methane and carbon dioxide mixtures was investigated experimentally at temperatures between 300°C and 800°C at atmospheric pressures using a Rh/γAl₂O₃ monolith catalyst. CH₄:CO₂ ratios of 1:1 and 1.4:1 were tested. The Rh catalyst reached equilibrium conversions of CH₄ and CO₂ to H₂ and CO for both CH₄:CO₂ ratios. Equilibrium analysis shows that carbon formation is likely for dry reforming but not for auto-thermal reforming. Experimentally, carbon formation was seen after long-term exposure to 1.4:1 CH₄:CO₂ ratios without oxygen, but the catalyst has shown the ability to be regenerated in air. Auto-thermal tests, with and without external heat input, operating at an equivalence ratio of 4.3 (O₂:CH₄=0.46) and maintaining the CH₄:CO₂ ratio of either 1:1 or 1.4:1, did not show signs of carbon formation or deactivation. ATR experiments resulted in H₂:CO ratios between 1.0 and 2.0 that can be tuned depending on the monolith temperature, beneficial in the case of downstream Fischer–Tropsch processes. For the auto-thermal experiments, theoretical reaction extents were calculated based on experimental data and showed two primary regimes in catalyst operation: a CH₄ combustion and partial oxidation regime, and reforming and water–gas shift regime.

Keywords: Auto-thermal reforming; Dry reforming; Landfill gas; Rhodium monolith catalyst

Integration of C–C coupling reactions of biomass-derived oxygenates to fuel-grade compounds by Elif I. Gürbüz; Edward L. Kunkes; James A. Dumesic (pp. 134-141).

Ceria-zirconia mixed oxides with different compositions including pure ceria and pure zirconia were prepared and characterized using temperature-programmed desorption (TPD) of CO₂ and NH₃, X-ray diffraction (XRD), and BET surface area measurements. Bi-functional catalysts for C–C coupling of ketones by aldol condensation/hydrogenation were prepared by depositing palladium on these ceria-zirconia mixed oxides, and these catalysts were studied for the conversion of 2-hexanone, a representative ketone that can be derived from sugars in biomass. The Pd/ZrO₂ catalyst showed the best resistance to inhibition by CO₂, an important factor in catalyst performance because of the presence of CO₂ in biomass-derived feed streams. Furthermore, this catalyst displayed high activity for aldol condensation, as well as good resistance to inhibition by water. These properties make Pd/ZrO₂ a desirable catalyst for integration in a single reactor of aldol condensation/hydrogenation reactions with ketonization processes, the latter of which convert carboxylic acids to ketones plus CO₂ and H₂O. The feasibility of this integration was studied with the mixture of a carboxylic acid (butanoic acid) and a ketone (2-hexanone) in a double bed system, and the integrated process showed high activity as well as selectivity to C–C coupling products.

Keywords: Aldol condensation; Ceria; Zirconia; CO; ₂; inhibition; Water inhibition

Photocatalytic reduction of Cr(VI) on WO₃ doped long TiO₂ nanotube arrays in the presence of citric acid by Lixia Yang; Yan Xiao; Shaohuan Liu; Yue Li; Qingyun Cai; Shenglian Luo; Guangming Zeng (pp. 142-149).

Photoreduction of Cr(VI) was successfully achieved on WO₃ doped TiO₂ nanotube (NT) arrays in the presence of citric acid. WO₃ doped TiO₂ NT arrays were fabricated by annealing anodic titania NTs that were preloaded with peroxotungstic acid. Driven by electrostatic force, the negatively charged peroxotungstic acid sol uniformly clung to the positively charged titania NT arrays, causing a solid solution of WO₃ and TiO₂ after annealing. The citric acid plays an important role in the photoreduction of Cr(VI): (i) it works as a sacrificial electron donor to deplete the photogenerated holes from the excited TiO₂; and (ii) it takes part in the redox with Cr(VI) under UV illumination because of its electron rich property. The photochemical-reduction rate of Cr(VI) in citric acid under simulated solar light was 6.9μg/Lmincm². Subtracting the part mentioned above, the reduction rate of Cr(VI) due to photogenerated electrons from excited photocatalysts increased from 8.3μg/Lmincm² on TiO₂ NTs to 31.6μg/Lmincm² on WO₃/TiO₂ NTs containing 1at% of W. The net Cr(VI) reduction rate on WO₃/TiO₂ NT arrays is 3.76 times that on the unmodified TiO₂ NTs. Since both WO₃ and TiO₂ can be excited by UV light, the enhanced photoactivity of WO₃/TiO₂ is attributed to the increased probability of charge–carrier separation and the extended photo-response spectrum in visible light region due to the doping of WO₃ (band gap: 2.6eV).

Keywords: WO; ₃; TiO; ₂; nanotube arrays; Cr(VI); Photocatalytic reduction

Highly active WO₃ semiconductor photocatalyst prepared from amorphous peroxo-tungstic acid for the degradation of various organic compounds by Kazuhiro Sayama; Hiroki Hayashi; Takeo Arai; Masatoshi Yanagida; Takahiro Gunji; Hideki Sugihara (pp. 150-157).

The photocatalytic activity and physical properties on WO₃ photocatalysts prepared by various methods were investigated. WO₃ photocatalyst (WO₃(PA)) prepared from aged amorphous peroxo-tungstic acid showed the highest activity for hexane degradation, which was ∼6 times higher than that of commercial WO₃, and exhibited a strong absorption in visible light region. WO₃(PA) loaded with CuO as co-catalyst showed a high activity for the complete oxidation of various organic compounds into CO₂, as compared with the activities of commercial or homemade WO₃ catalysts and N-doped TiO₂. The high activity of WO₃(PA) was explained by high surface area, good crystallinity, and efficient light absorption in visible light region. The light absorption of WO₃(PA) powder was probably improved because of a decrease in surface reflection at the smooth and porous surface of WO₃(PA) and because of its increased light path length.

Keywords: WO; ₃; Semiconductor; Photocatalyst; Degradation

Novel preparation of nanosized mesoporous SnO₂ powders: Physicochemical and catalytic properties by Momtchil Dimitrov; Tanya Tsoncheva; Shaofeng Shao; Ralf Köhn (pp. 158-165).

Two series of catalytically active SnO₂ powders were prepared from tin(IV) tert-butoxide and tin(IV) chloride as tin precursors. A part of the synthesized samples were additionally subjected to specific treatments during the preparation—a treatment at constant humidity and temperature and/or a “step calcination”. The obtained samples were characterized by powder X-ray diffraction, nitrogen physisorption, transmission electron microscopy and were studied in the total oxidation of ethyl acetate. The use of these specific treatments leads to materials that differ substantially in their textural characteristics and catalytic properties. The highest catalytic activity and selectivity are obtained for samples prepared from tin(IV) tert-butoxide after the “step calcination” treatment.

Keywords: Nanocrystallites; Mesoporous; SnO; ₂; Oxidation; Catalysis

Preparation, testing and performance of a TiO₂/polyester photocatalyst for the degradation of gaseous methanol by M.I. Mejía; J.M. Marín; G. Restrepo; L.A. Rios; C. Pulgarín; J. Kiwi (pp. 166-172).

TiO₂ modified polyester photocatalysts were prepared by immersion, drying and curing of the polyester in TiO₂ containing suspensions under different experimental conditions. The structure of TiO₂ layers on the polyester varied according to the time of immersion and type of polyester used. The optical microscopy (OM) and scanning electron microscopy (SEM) show a more uniform distribution of TiO₂ on the polyester prepared by sol–gel as compared to the silicone as a binder. Energy diffuse spectroscopy (EDS) and infrared (ATR-FTIR) spectroscopy confirmed that TiO₂ bonded to the polyester textile. BET analysis showed that TiO₂–SiO₂ applied by sol–gel on polyester led to a higher surface area compared to silicon. Photodegradation of gaseous methanol mediated by the TiO₂–polyester was followed by gas chromatography (GC) and ATR-FTIR spectroscopy. The TiO₂–polyester sample prepared by sol–gel with an immersion time of 11h exhibited the most favorable photocatalytic performance during methanol degradation in the gas phase. The best performance during methanol photodegradation was observed for the smallest agglomerate TiO₂ size. The structure–reactivity relationship for different photocatalysts was systematically explored. Quantitative evaluation of the cluster size, immersion time and catalyst loading provided the evidence for the best performance for methanol degradation by the catalyst prepared at 11h immersion time. The photocatalytic activity of the TiO₂–polyester catalyst was observed to remain stable during methanol over several degradation cycles.

Keywords: Sol–gel; Photocatalysis; Polyester-TiO; ₂; Methanol photodegradation

Hydrogen catalytic effects of nanostructured alloy particles in spent fuel on radionuclide immobilization by D. Cui; J. Low; V.V. Rondinella; K. Spahiu (pp. 173-178).

For the first time, hydrogen catalytic effects of fission product alloy particles nondestructively extracted from spent nuclear fuel were demonstrated. The redox sensitive radionuclides at oxidized forms Se(IV), Tc(VII), U(VI), Np(V) and Pu(VI) were found to be stable in a solution saturated with a gas mixture (Ar+10% H₂+0.03% CO₂) but rapidly immobilized in the same solution when contacted with the particles. In comparison, a synthetic alloy sample with similar elemental composition as the alloy particles generated in nuclear fuel displayed a smaller, but unequivocal catalytic effect. The smaller catalytic effect of synthetic alloy was apparently enhanced by a β-radiation source. The information obtained in this work contributes to improved understanding of the redox chemistry of radionuclides in nuclear waste geologic repository environments and, in particular, of the catalytic properties of these unique alloy particles.

Keywords: Radioactive catalyst; Nanoparticle; Hydrogen; Fission product; Nuclear waste

Tailored activated carbons as catalysts in biodecolourisation of textile azo dyes by Gergo Mezohegyi; Filomena Gonçalves; José J.M. Órfão; Azael Fabregat; Agustí Fortuny; Josep Font; Christophe Bengoa; Frank Stuber (pp. 179-185).

Anaerobic reduction of two textile azo dyes (Orange II and Reactive Black 5) was investigated in upflow stirred packed-bed reactors (USPBRs) with biological activated carbon (BAC) system. The bioreactors were prepared with tailored activated carbons (ACs) having different textural properties and various surface chemistries. A kinetic model proposed previously was able to describe the catalytic azo reduction in all cases. Decolourisation with very high reduction rates took place in the case of each AC. Best dye removals were ensured by the AC having the highest surface area: conversion values above 88% were achieved in the case of both azo dyes at a space time of 0.23min or higher, corresponding to a very short hydraulic residence time of about 0.30min at the most. The decolourisation rates were found to be significantly influenced by the textural properties of AC and moderately affected by its surface chemistry. The results confirmed the catalytic effects of carbonyl/quinone sites and, in addition, delocalized π-electrons seemed to play a role in the catalytic reduction in the absence of surface oxygen groups.

Keywords: Azo dye; Reduction; Activated carbon; Packed-bed reactor; Surface chemistry

Lowering of photocatalytic activity of TiO₂ particles during oxidative decomposition of benzene in aerated liquid by Thuan Duc Bui; Akira Kimura; Shigeru Ikeda; Michio Matsumura (pp. 186-191).

TiO₂-photocatalyzed reaction was conducted in pure benzene in which TiO₂ particles were suspended. Benzene was oxidatively decomposed into CO₂, as most of organic compounds. However, the rate of CO₂ evolution from benzene was gradually lowered as the reaction continued, which was in contrast to the cases of other non-aromatic organic compounds, such as alcohols or acids. To clarify the reason for the decrease in activity of TiO₂, intermediates produced in the solution phase and on the surface of TiO₂ were analyzed using chemical and physical techniques. Several kinds of intermediates were identified: phenolic compounds, aldehydes, carboxylic acids, and polymeric substance. Of these products, catechol and polymeric substance, which were observed only on the surface of TiO₂ powder, were found to be responsible for the lowering of the photocatalytic activity of TiO₂.

Keywords: TiO; ₂; Benzene; Catechol; Polymer; Deactivation

Kinetics and initial photocatalytic pathway of tryptophan, important constituent of microorganisms by L. Elsellami; F. Vocanson; F. Dappozze; R. Baudot; G. Febvay; M. Rey; A. Houas; C. Guillard (pp. 192-199).

The adsorption equilibrium in the dark and under UV light, the kinetic of photocatalytic oxidation and the main initial pathways of tryptophan photocatalytic degradation has been investigated in aerated TiO₂ Degussa P-25 aqueous suspensions illuminated at λ>340nm. Tryptophan has been chosen as a model of organic compounds of amino acids, elemental constituents of DNA, microorganisms, e.g. bacteria, fungi, virus among others to better understand their photocatalytic degradation.Langmuir and Langmuir–Hinshelwood models have been used to determine the adsorption, the rate constants and the surface coverage of TiO₂. Despite a low coverage of the TiO₂ surface in the dark a high photocatalytic degradability and initial mineralization occurred. However, the surface coverage of TiO₂ was about doubled under UV light suggesting the formation of active sites under irradiation.LC–MS, LC–UV with or without derivatization analyses allowed us to identify, mono-, di- and tri-hydroxylated compounds, deamination of heterocycle, the formation of six organic acid, oxalic, oxamique, lactic, formic, acetic and propanoic acids and of three linear amino acids, serine, aspartic acid and glycine. A degradation mechanism is proposed to the formation of oxamic acid.The study of the mineralization of carbon and nitrogen showed the presence of trace of organic molecules mineralizable with difficulty. Nitrogen atoms were predominantly photoconverted into NH₄⁺. After more than 95% of carbon mineralization, NH₄⁺/NO₃⁻ ratio was 4.The identification of the photocatalytic products, their evolution and the TOC evolution indicated three initial competitive pathways: about 50% of hydroxylation with 6–7% of the hydroxylation of carbon bearing NH₂ and COO⁻, about 30% of decarboxylation and less than 20% of nitrogen–carbon (N–C) cleavage.

Keywords: Photocatalysis; Amino acids; Tryptophan; Chemical pathways; Intermediates

Efficient polymer-based nanocatalysts with enhanced catalytic performance in wet air oxidation of phenol by Esther M. Sulman; Valentina G. Matveeva; Valentin Yu. Doluda; Alexander I. Sidorov; Natalia V. Lakina; Alexei V. Bykov; Michael G. Sulman; Pyotr M. Valetsky; Leonid M. Kustov; Olga P. Tkachenko; Barry D. Stein; Lyudmila M. Bronstein (pp. 200-210).

In this paper we report the synthesis of robust and efficient nanocatalysts based on Pt-containing nanoparticles (NPs) formed in the pores of hypercrosslinked polystyrene (HPS) and their catalytic performance in the phenol CWAO under mild conditions. The Pt species were incorporated in HPS using wet impregnation of platinic acid in tetrahydrofuran followed by NaHCO₃ treatment. The catalysts containing from 0.11 to 4.85wt.% of Pt were studied by X-ray fluorescence analysis, transmission electron microscopy, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and liquid nitrogen physisorption methods. The NP sizes were found to be independent of the amount of platinic acid used for impregnation, but rather controlled by the pores of HPS. Three types of Pt species: Pt(0), Pt(II), and Pt(IV), constituted the NP composition. The effects of the phenol and catalyst initial concentrations and temperature were investigated in the phenol CWAO. Removal of 97% of the phenol with 94.2% selectivity to CO₂ and H₂O were observed for the most active catalyst containing 0.95wt.% Pt. These parameters are significantly higher than those for the conventional Al₂O₃–Pt catalyst with the similar amount of the active metal or for Pt(5%)/activated carbon.

Keywords: Platinum; Nanoparticles; Catalytic wet air oxidation; Phenol

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Applied Catalysis B, Environmental (v.94, #1-2)