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Applied Catalysis B, Environmental (v.115-116, #)

Contents Continued (pp. i).

Editorial Board (pp. i).

Editorial Board (pp. co2).

Contents (pp. co4).

Glycerol oxidation with gold supported on carbon xerogels: Tuning selectivities by varying mesopore sizes by Elodie G. Rodrigues; Manuel F.R. Pereira; José J.M. Órfão (pp. 1-6).

Display Omitted► Gold supported on carbon xerogels are efficient catalysts for glycerol oxidation. ► Textural properties of support play a key role in the distribution of products obtained. ► Carbon xerogels with wide mesopores favor oxidation towards dihydroxyacetone. ► Selectivities correlate with mesopore sizes of different carbon supports.Two carbon xerogels (CX) with different pore size distributions were prepared by the conventional approach (condensation of resorcinol and formaldehyde). The key variable to control those sizes is the pH of the aqueous solution. Gold nanoparticles were supported on the prepared CXs by the sol immobilization method and tested in the selective oxidation of glycerol, with the main purpose of evaluating the influence of the textural properties on the activity and selectivity. Mesopore sizes of the support have a strong effect on the distribution of products: wide pores enhance the formation of dihydroxyacetone whereas narrow mesopores favor the oxidation towards glyceric acid. Additionally, the selectivity results obtained with carbon xerogels were compared with those achieved with other carbon supports (activated carbon and multi-walled carbon nanotubes) and the same trend was observed. Therefore, it seems that the distribution of products can be controlled by the adequate choice of the support. For this purpose, carbon xerogel is a promising material since its pore size can be easily modified in a controllable way during the preparation stage.

Keywords: Glycerol; Oxidation; Gold; Carbon xerogel; Mesopore size; Selectivity

Supported Pd catalysts for solvent-free benzyl alcohol selective oxidation: Effects of calcination pretreatments and reconstruction of Pd sites by Xueming Wang; Guangjun Wu; Naijia Guan; Landong Li (pp. 7-15).

Display Omitted► Ideal green oxidation of benzyl alcohol catalyzed by supported Pd catalysts. ► Calcination pretreatments show great effects on catalytic activity. ► Palladium sites undergo reconstruction during reaction. ► Defect sites on Pd (111) proposed to be the primary sites for benzyl alcohol oxidation.Pd catalysts supported on Al₂O₃ and TiO₂ have been prepared by wet impregnation and studied for the solvent-free selective oxidation of benzyl alcohol by molecular oxygen. High activity as well as high selectivity to benzaldehyde can be obtained and the calcination pretreatments show distinct effects on the catalytic activities of supported Pd catalysts. Supported Pd catalysts before and after benzyl alcohol oxidation are characterized by means of XPS, FTIR spectra of CO adsorption and O₂-TPD. The results clearly show that the palladium sites in supported Pd catalysts undergo reconstruction during benzyl alcohol oxidation. Based on the catalytic and characterization results, the possible benzyl alcohol oxidation reaction pathways and the active palladium sites in supported Pd catalysts for benzyl alcohol oxidation are discussed.

Keywords: Supported Pd catalysts; Selective oxidation; Calcination pretreatments; Reconstruction

Synthesis of cerium-doped MCM-41 for ozonation of p-chlorobenzoic acid in aqueous solution by Jishuai Bing; Laisheng Li; Bingyan Lan; Gaozu Liao; Junyu Zeng; Qiuyun Zhang; Xukai Li (pp. 16-24).

Display Omitted► This work solves the leaching problems of catalyst's active components. ► Ce-MCM-41 was first used as a heterogeneous catalyst in ozonation process. ► Ce-MCM-41 showed the better activity and stability than Ce/MCM-41. ► Cerium leaching of Ce-MCM-41 was greatly reduced compared with that of Ce/MCM-41. ► Cerium leaching of Ce-MCM-41 was below detection limit after being reused.Cerium-doped MCM-41 (Ce-MCM-41) was prepared by a hydrothermal method and its catalytic activity for ozonation of p-chlorobenzoic acid ( p-CBA) in aqueous solution was studied. For comparison, cerium-loaded MCM-41 (Ce/MCM-41) was prepared by a dipping method. Ce-MCM-41 was characterized by the low and wide angle X-ray powder diffraction (XRD), nitrogen adsorption–desorption, transmission electron microscopy (TEM) and ultraviolet–visible diffuse reflection spectrum (UV–vis DRS). The results showed that the material retained the highly ordered mesopore structure of MCM-41 and had a surface area of 852m²g⁻¹. Cerium was incorporated into the framework of MCM-41, locating at tetrahedrally coordinated sites. The cerium doping content, initial pH of aqueous solution and reaction temperature played important roles in catalytic ozonation of p-CBA. Under the chosen conditions (1.39mgl⁻¹ ozone dosage, 10mgl⁻¹ p-CBA solution and 1gl⁻¹ catalyst dosage), the high mineralization rate (86%) was achieved by Ce-MCM-41/O₃ process at 60min reaction time, only 52% by O₃ alone. The combination of Ce-MCM-41 and O₃ exhibited a significant synergetic effect. Ce-MCM-41 showed the better activity and stability than cerium-loaded MCM-41(Ce/MCM-41) during catalytic ozonation of p-CBA, its cerium leaching was greatly reduced (only 0.085mgl⁻¹) and below detection limit after being reused, compared with that of Ce/MCM-41 (0.44mgl⁻¹) with the presence of the same theoretical cerium content. TOC removal rate slightly decreased from 86% to 81% and kept stable after Ce-MCM-41 being re-utilized two times, which illustrated that Ce-MCM-41 was a kind of promising catalyst for ozonation of p-CBA. The addition of Ce-MCM-41 significantly improved ozone decomposition into HO in aqueous solution and reduced ozone concentration in equilibrium.

Keywords: Ce-MCM-41; Catalytic ozonation; p; -Chlorobenzoic acid

Electrocatalytic oxidation of ethanol on Pt, Pt-Ru and Pt-Sn nanoparticles in polymer electrolyte membrane fuel cell—Role of oxygen permeation by Andrzej Jablonski; Adam Lewera (pp. 25-30).

Display Omitted► Effects of oxygen permeation in direct ethanol fuel cell has been investigated. ► Oxygen permeating from cathode side is able to parasitically oxidize ethanol. ► Acetic acid is produced on Pt surface exclusively due to oxygen permeation. ► Oxygen permeation can be held liable for the discrepancy observed in literature. ► Oxygen permeates thru Nafion 117 at least at 2.5–3.5mA/cm² rate.We have recently shown that in low temperature, polymer-electrolyte membrane direct ethanol fuel cells oxygen permeating from cathode is able to chemically oxidize ethanol at the anode surface . Such process is responsible for significant amounts of acetaldehyde and acetic acid present at anode outlet, which are not related to the flow of electric current in external circuit. Here, for the first time, we report unbiased distribution of products of ethanol electrooxidation on Pt, Pt-Ru and Pt-Sn as a function of fuel cell voltage (under load) and temperature. We show here that for Pt anode and for cell voltage above 300mV oxidation of ethanol to acetic acid does not occur as a result of electric current flow, but it is caused exclusively by chemical reaction between ethanol and oxygen permeating from cathode. This explains the obvious contradiction, which can be found in scientific literature regarding ethanol electrooxidation on Pt. Namely acetic acid is not observed in spectroelectrochemical, ex situ experiments in conditions comparable to working direct ethanol fuel cell, where it is detected in case of in situ, fuel cell experiments.Relation between unbiased distribution of products and anode catalyst's type, cell voltage, cell discharge current and temperature is also discussed. Oxygen permeation via Nafion 117 at 80°C expressed in unit of electric current has been estimated to be at least 2.5–3.5mA/cm².

Keywords: Fuel cells; Oxygen permeation; Ethanol electrooxidation; Platinum; Acetaldehyde; Acetic acid; Gas chromatography

Semiconductor oxides-sensitized photodegradation of fenamiphos in leaching water under natural sunlight by José Fenoll; Pilar Hellín; Carmen María Martínez; Pilar Flores; Simón Navarro (pp. 31-37).

Photocatalytic degradation of fenamiphos in leaching water by using semiconductor oxides. ZnO was the most efficient for catalyzing the removal of fenamiphos and its metabolites. Total degradation of fenamiphos derivatives was achieved for the tandem ZnO/Na₂S₂O₈.Display Omitted► Heterogeneous photocatalytic oxidation of fenamiphos in water. ► ZnO and TiO₂ strongly enhanced photodegradation in comparison with WO₃ and SnO₂. ► Half-lives for fenamiphos in the presence of ZnO and TiO₂ were about 1–3min. ► Complete disappearance of fenamiphos metabolites was achieved only in the presence of ZnO.The photocatalytic degradation of fenamiphos in leaching water has been studied using zinc oxide (ZnO), different mixed-phase titanium dioxide (TiO₂), tungsten(VI) oxide (WO₃), and tin(IV) oxide (SnO₂) at pilot plant scale under natural sunlight. Photocatalytic experiments showed that the addition of semiconductors in tandem with the oxidant (Na₂S₂O₈) strongly enhances the degradation rate of fenamiphos in comparisons carried out with photolytic tests. The primary degradation of fenamiphos followed a pseudo-first order kinetics. The time required for 50% degradation was in the range 1–3min for ZnO and TiO₂. The main photocatalytic intermediates (fenamiphos-sulfoxide and fenamiphos sulfone) detected during the degradation of fenamiphos were identified. Comparison of catalysts showed that ZnO is the most efficient for catalyzing the removal of fenamiphos and their metabolites. Thus, complete disappearance of all the compounds studied achieved after 240min of illumination in the ZnO/Na₂S₂O₈ system.

Keywords: Water detoxification; Fenamiphos; Fenamiphos sulfoxide; Fenamiphos sulfone; Photocatalytic oxidation; Semiconductor materials

Solar photocatalysis treatment of phytosanitary refuses: Efficiency of industrial photocatalysts by Gael Plantard; Thomas Janin; Vincent Goetz; Stephan Brosillon (pp. 38-44).

Display Omitted► Photo-sensitivity of two TiO₂ catalysts (with a granulometric ratio of 1000) are studied. ► Kinetics of degradation linearly depend on the quantity of photons used. ► Two catalysts, achieved similar performances in their optimal configurations.In the field of advanced oxidization processes based on solar radiation, heterogeneous solar catalysis involves exciting a photocatalyst with UV rays and one of the major problem encountered is optimizing the use of the sunlight. Catalysts in suspension develop the best ability to degrade polluting molecules. In this study, two TiO₂ catalysts in suspension which develop the best ability to degrade polluting molecules, with a granulometric ratio of 1000, have been investigated. All the experiments were performed under natural sunlight in a photoreactor consisting of three identical but independent reactors. A simple kinetic model of degradation is purposed for the media each in its optimal configuration, considering the irradiation, the catalyst and pollutant concentrations. First of all, we show that the kinetics of degradation decline as a function of the quantity of photons used and that the two catalysts (with a granulometric ratio of 1000), achieved similar performances when they were used in their optimal configurations. Secondly, the logarithm of the concentration of pyrimethanil decreased linearly as a function of the combinationQUVCTiO2m. This indicates the direct dependence of the quantity degraded on the quantity of UV energy effectively available for the photocatalytic reaction.

Keywords: Solar photocatalysis; Pesticides; Photocatalyst efficiency; Kinetic model

Investigation of iron oxide reduction by ethanol as a potential route to produce hydrogen by M.G. Rosmaninho; F.C.C. Moura; L.R. Souza; R.K. Nogueira; G.M. Gomes; J.S. Nascimento; M.C. Pereira; J.D. Fabris; J.D. Ardisson; M.S. Nazzarro; K. Sapag; M.H. Araújo; R.M. Lago (pp. 45-52).

In this work, a novel way to indirectly store and produce H₂ from ethanol was investigated using a two-step process based on the reduction of iron oxide followed by oxidation with H₂O. The reduction of different iron oxides, i.e., Fe₂O₃, Fe₃O₄ and FeOOH, with ethanol to produce Fe^o was investigated. TPRe (Temperature Programmed Reactions) and Mössbauer and XRD analyses showed that ethanol reduces Fe₂O₃ sequentially to Fe₃O₄ at 350–500°C, to Fe₃O₄/FeO at 500–600°C and finally to Fe^o at 700°C. The formed Fe^o can then be oxidized by H₂O to produce H₂ and Fe₃O₄, as shown by Mössbauer and XRD analyses. Cyclic experiments showed that iron could be consecutively reduced/oxidized at least 5 times without any significant decrease in H₂ production after the second cycle. However, reactions of Fe₂O₃ with ethanol at higher temperatures, i.e., 800 and 900°C, led to the formation of iron carbide and significant carbon deposition. XPS, SEM, TEM, Raman and TG showed 24–28wt% carbon content, particularly on the surface as nanofibers and as amorphous and graphitic carbon.

Keywords: Hydrogen production; Hydrogen storage; Ethanol; Iron oxide

MO_x (M=Mn, Fe, Ni or Cr) improved supported Co₃O₄ catalysts on ceria–zirconia nanoparticulate for CO preferential oxidation in H₂-rich gases by Zhongkui Zhao; Xiaoli Lin; Ronghua Jin; Guiru Wang; Turghun Muhammad (pp. 53-62).

Display Omitted► MnO_x remarkably enhances catalytic activity of supported Co₃O₄ catalysts for CO PROX. ► The appropriate Co/Mn ratio and loading are essential to the modified catalysts. ► The active species reducibility and dispersity strongly affect catalytic properties. ► Co-Mn interaction significantly improves the Co₃O₄ dispersion and the reducibility. ► Co³⁺ is main active species, and the presence of Mn⁴⁺/Mn³⁺ benefits for the reaction.This approach dealt with the modification of our developed Co₃O₄/Ce_0.85Zr_0.15O₂ catalysts with transition metal oxides MO_x (M=Mn, Fe, Ni or Cr) for CO preferential oxidation (CO PROX) in H₂-rich gases. Results showed that just MnO_x modification remarkably broadened the temperature window of 100% CO conversion, also better than those in the report about Co-Mn composite catalysts from another research group. And even in the presence of H₂O and CO₂, the 175–225°C temperature range for almost 100% CO conversion can be achieved over the optimized catalyst. Moreover, the addition of MnO_x significantly improved the catalytic activity and selectivity, which was dramatically better than those of the supported MnO_x or Co₃O₄ catalysts on ceria–zirconia nanoparticulate, indicating the existence of the remarkable Co-Mn synergistic effect. The MnO_x modified supported Co₃O₄ catalysts exhibited outstanding catalytic properties for CO PROX reaction, which was strongly dependent on the reducibility and dispersion of the active species affected by the Co/Mn atomic ratio and loading. The XRD and H₂-TPR techniques were performed to reveal the effect of structure–activity relationship on the catalytic properties. The analytic results presented that Co³⁺ was the main active species for CO PROX reaction, and the existence of Mn⁴⁺ and Mn³⁺ was also favorable to the reaction. The XRD and H₂-TPR characterization results affirmed the existence of strong interaction between Co and Mn, increasing the ratio of Co³⁺/Co²⁺ resulted from the electron transfer between Co²⁺ and Mn⁴⁺. Besides the improvement of Co₃O₄ dispersion and the enlargement of the Co³⁺/Co²⁺ ratio through Co-Mn interaction, the addition of MnO_x could improve the stability of the ceria–zirconia support through the metal–support interaction. As a result, the CO selective oxidation reaction was efficiently improved. The 16wt.%Co₃O₄-MnO_x/Ce_0.85Zr_0.15O₂ (Co/Mn=8:1) could be a quite potential catalyst for eliminating trace CO from H₂-rich gases.

Keywords: CO preferential oxidation; MnO; _x; modification; Ceria–zirconia; Co-Mn interaction; PEM fuel cell

Gas-phase hydrodeoxygenation of guaiacol over Fe/SiO₂ catalyst by R.N. Olcese; M. Bettahar; D. Petitjean; B. Malaman; F. Giovanella; A. Dufour (pp. 63-73).

Display Omitted► Guaiacol is a model molecule of lignin pyrolysis vapours. ► Guaiacol was hydrotreated using Fe/SiO₂ catalyst at 623–723K. ► These temperatures match with the temperature of lignin pyrolysis vapours. ► Fe/SiO₂ is a versatile and selective catalyst for benzene and toluene (BT) production. ► 38% of BT yield was achieved.Lignin could be an important green source for aromatic hydrocarbon production (benzene, toluene and xylenes, BTX). Catalytic hydrodeoxygenation (HDO) of guaiacol was studied over Fe/SiO₂ as a model reaction of lignin pyrolysis vapours hydrotreatment. The catalytic conditions were chosen to match with the temperature of never-condensed lignin pyrolysis vapours. The catalyst was characterised by XRD, Mössbauer spectroscopy, N₂ sorption and temperature programmed oxidation. A comparison is made with a commercial cobalt-based catalyst. Cobalt-based catalyst shows a too high production of methane. Fe/SiO₂ exhibits a good selectivity for BT production. It does not catalyse the aromatic ring hydrogenation. Temperature (623–723K) and space time (0.1–1.5g_cath/g_GUA) influence the aromatic carbon–oxygen bond hydrogenolysis reaction whereas H₂ partial pressure (0.2–0.9bar) has a minor influence. 38% of BT yield was achieved under the best investigated conditions. Reaction mechanisms for guaiacol conversion over Fe/SiO₂ are discussed.

Keywords: Green chemicals; Aromatic; Lignin; Bio-oils; Hydrotreatment; Catalyst; Iron

Photo-chargeable and dischargeable TiO₂ and WO₃ heterojunction electrodes by Hyunwoong Park; Ayoung Bak; Tae Hwa Jeon; Seungdo Kim; Wonyong Choi (pp. 74-80).

Display Omitted► TiO₂ and WO₃ mixed electrodes have bi-functionality of light conversion and storage. ► Electron flow between TiO₂ and WO₃ upon light on (photocharging) is demonstrated to be reversed upon light off (discharging). ► The mixed electrodes can be applied to anticorrosion of steel in the presence and absence of daylight. ► The charging/discharging behaviors are significantly affected by ratios of TiO₂ and WO₃ in weight and area.TiO₂ and WO₃ heterojunction electrodes are studied for their bi-functionality on harvesting light and storing energy. Both semiconductors are fabricated either ‘single’ (mixed) electrodes or two different electrodes galvanically coupled in a mixed electrolyte of 0.1M sodium formate and 0.1M sodium chloride. Irradiation of AM 1.5-light shifts the open circuit potentials (OCPs) of the mixed and coupled electrodes from around −0.1V_SCE (dark OCPs) to a potential range between −0.8 and −0.5V_SCE, which slowly return to their respective dark OCPs over a period of around 14h. Such discharging periods are significantly influenced by the irradiation (photocharging) time and weight or area ratios of TiO₂ and WO₃. When the TiO₂ and WO₃ mixed electrodes are galvanically coupled to stainless steel electrodes for application to anticorrosion, the mixed potentials of the couple are maintained at ca. −0.4V_SCE over 10h even after light off. The measured galvanic currents verify that the photogenerated electrons of TiO₂ flow to WO₃ (charging) and even overflow to the steel (cathodic protection) during the irradiation, while the stored electrons at WO₃ flow to the galvanically coupled steel electrodes directly or through the TiO₂ upon light off.

Keywords: Artificial photosynthesis; Discharging; Battery; Galvanic; Anticorrosion; Solar

One-step, hydrothermal synthesis of nitrogen, carbon co-doped titanium dioxide (N,CTiO₂) photocatalysts. Effect of alcohol degree and chain length as carbon dopant precursors on photocatalytic activity and catalyst deactivation by D. Dolat; N. Quici; E. Kusiak-Nejman; A.W. Morawski; G. Li Puma (pp. 81-89).

.Display Omitted► Optical and structural properties of N,CTiO₂ depend on the alcohol precursor used. ► N,CTiO₂ deactivates much less than TiO₂ P25 and has much higher activity after reuse. ► A new approach for the evaluation of the intrinsic photocatalytic activity is proposed. ► Photocatalytic activity of slurries is measured at equal rate of photon absorption.A one-step, hydrothermal method for the synthesis of nitrogen, carbon co-doped titanium dioxide (N,CTiO₂) photocatalysts is demonstrated. The incorporation of nitrogen from ammonia and carbon from alcohols with different chain length (methanol, ethanol, isopropanol, 1-butanol, 2-butanol, tert-butanol) used as carbon precursors was confirmed by FTIR/DRS and XPS analyses. The UV–vis/DR absorption spectra of the modified photocatalysts extended into the visible. XRD, BET and Zeta SizerNano techniques were used for the characterization of the modified photocatalysts. The crystallite size of N,CTiO₂ was not affected by the nature of the alcohol or the pressure acquired during the modification process but surface area, particle size (crystal agglomerate) and anatase content increased with synthesis pressure. In contrast with other studies in literature, the photoactivity of the different synthesized materials was evaluated at a constant volumetric rate of photon absorption (VRPA) in an annular photoreactor. This innovative method allows the evaluation of the intrinsic photoactivity of each material. As a result, the effect of N,C-co-modification on the TiO₂ photoactivity was evaluated without interference from the amount of radiation absorbed by each suspended powder since the total radiant energy absorbed by each slurry suspension was kept constant. Phenol decomposition confirmed that activity increased with the chain length of the alcohol precursor. The highest intrinsic photoactivity was for N,CTiO₂ prepared from 2-butanol, and 1-butanol as carbon precursor which also exhibited much stronger resistance to deactivation during multiple catalyst reuse compared to pristine TiO₂ and commercial Degussa P25 photocatalysts.

Keywords: Photocatalysis; TiO; ₂; Degradation; Nitrogen/carbon co-modification; Catalyst lifetime; Intrinsic photocatalytic activity; Volumetric rate of photon absorption

Carbon spheres supported visible-light-driven CuO-BiVO₄ heterojunction: Preparation, characterization, and photocatalytic properties by Weirong Zhao; Yan Wang; Yong Yang; Jing Tang; Yanan Yang (pp. 90-99).

Display Omitted► Carbon spheres supported CuO-BiVO₄ heterojunction was synthesized. ► Carbon spheres roles as dispersing support and photosensitizer. ► Composite structure plays a key role in the enhancement of photocatalytic activities. ► A reasonable photodegradation mechanism based on electron transfer was proposed.To utilize visible light more effectively in photocatalytic reactions, carbon-supported CuO-BiVO₄ (CuO-BVO@C) composite photocatalyst was prepared by hydrothermal process and impregnation technique. The photocatalytic activities of as-prepared catalysts were evaluated by degradation of methylene blue (MB) in aqueous solution under visible light irradiation, it was found that CuO-BVO@C exhibits the highest photocatalytic degradation activity with the pseudo-first-order rate constant K_a five times higher than pure BiVO₄, which could be assigned to the synergistic effect of CuO-BiVO₄ heterojunction and carbon spheres. The characterization of photocatalysts by a series of joint techniques, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–vis diffuse reflectance spectra, PL spectra and electrochemistry technology, discloses that carbon spheres play two crucial roles in enhancing of photocatalytic activity. One is to act as a dispersing support to suppress the grain growth, the other is to act as a photosensitizer to transfer the electrons to CuO-BiVO₄ heterojunction, which narrows the band gap of BiVO₄, hinders the electron–hole pair's recombination, extends the absorption range of visible light, and improves the photocatalytic performance of catalyst. The photocatalytic degradation pathways mainly involve the formation and reaction ofOH radicals. Based on the experimental results of electron spin-resonance spectroscopy, a reasonable mechanism was also proposed to elucidate the role of carbon spheres in the CuO-BVO@C composite as a photocatalyst for degradation of organic pollutants.

Keywords: Photocatalysis; Methylene blue; Photodegradation; Photosensitizer; Electron transfer

A superior Ce-W-Ti mixed oxide catalyst for the selective catalytic reduction of NO_x with NH₃ by Wenpo Shan; Fudong Liu; Hong He; Xiaoyan Shi; Changbin Zhang (pp. 100-106).

Display Omitted► Ce-W-Ti mixed oxide catalyst prepared by homogeneous precipitation method. ► Excellent NH₃-SCR activity and N₂ selectivity in a wide temperature range. ► Extremely high durability to space velocity. ► Introduction of W species could increase the amount of active sites, oxygen vacancies, and Brønsted and Lewis acid sites.A superior Ce-W-Ti mixed oxide catalyst prepared by a facile homogeneous precipitation method showed excellent NH₃-SCR activity and 100% N₂ selectivity with broad operation temperature window and extremely high resistance to space velocity, which is a very promising catalyst for NO_x abatement from diesel engine exhaust. The excellent catalytic performance is associated with the highly dispersed active Ce and promotive W species on TiO₂. The introduction of W species could increase the amount of active sites, oxygen vacancies, and Brønsted and Lewis acid sites over the catalyst, which is also beneficial to improve the low temperature activity by facilitating “fast SCR” reaction and enhance both of the high temperature activity and N₂ selectivity simultaneously by inhibiting the unselective oxidation of NH₃ at high temperatures.

Keywords: Ce-W-Ti mixed oxide; SCR; Nitrogen oxides; Homogeneous precipitation method; Diesel engine exhaust

Finding the best Fe²⁺/Cu²⁺ combination for the solar photoelectro-Fenton treatment of simulated wastewater containing the industrial textile dye Disperse Blue 3 by Ricardo Salazar; Enric Brillas; Ignasi Sirés (pp. 107-116).

Display Omitted► Dye treatment by solar photoelectro-Fenton (SPEF) catalyzed by Fe²⁺ and Cu²⁺ ions. ► Treatment of simulated wastewaters of a textile company with Disperse Blue 3. ► Cu²⁺ favors the Fe²⁺ regeneration and easier oxidation of Cu(II) complexes byOH. ► Reaction scheme including anthraquinones, heterocycles and phthalic acid derivatives. ► Overall decolorization and mineralization with relatively low energy consumptions.The performance of the solar photoelectro-Fenton (SPEF) process with Fe²⁺ and Cu²⁺ as metal co-catalysts and its application to the treatment of solutions simulating Disperse Blue 3 (DB3) dye bath effluents of a Chilean textile company are reported in this paper. The trials were carried out with 2.5l solutions using a solar pre-pilot plant containing an electrochemical reactor with a 20cm² BDD anode and air-diffusion cathode, coupled to a 600ml solar photoreactor. DB3 solutions with 0.1M Na₂SO₄ at pH 3.0 were electrolyzed to assess the effect of the applied current density, catalyst nature and concentration and dye content on the decolorization rate, dye removal and total organic carbon (TOC) abatement. The SPEF treatments using 0.5mM Fe²⁺+0.1mM Cu²⁺ led to the quickest degradation kinetics, mainly due to the concomitant action of UV photolysis and the generated oxidizing hydroxyl radicals on the organic molecules and/or their Cu(II) and Fe(III) complexes. Based on the identification of up to 15 aromatic by-products by GC–MS, a reaction scheme for DB3 degradation has been proposed. The progressive color and TOC removal of DB3 solutions were due to various changes undergone by the initial anthraquinonic structure, including the modification/addition of auxochromes giving 6 anthraquinonic by-products and its cleavage to yield compounds with 2 aromatic rings due to intermolecular cyclization or 1 aromatic ring mainly in the form of phthalic acid derivatives. Upon cleavage of these aromatics, maleic, oxalic, oxamic, pyruvic and acetic acids were formed. NO₃⁻ ions were released to a larger extent than NH₄⁺ ions. The great efficacy of SPEF with Fe²⁺ and Cu²⁺ was demonstrated for simulated wastewater containing DB3 and industrial surfactants and additives at 50mAcm⁻², allowing their total decolorization and almost overall mineralization in only 150 and 360min, with an energy consumption of 11.0 and 26.4kWhm⁻³, respectively.

Keywords: Anthraquinonic dyes; Boron-doped diamond anode; Metal catalysts; Solar photoelectro-Fenton; Wastewater treatment

Gold catalysts supported on nanostructured Ce–Al–O mixed oxides prepared by organic sol–gel by Elena Smolentseva; Andrey Simakov; Sergey Beloshapkin; Miguel Estrada; Eunice Vargas; Vladimir Sobolev; Roman Kenzhin; Sergio Fuentes (pp. 117-128).

Display Omitted► Ce–Al oxides prepared by sol–gel are effective in the formation of active Au species for CO oxidation. ► The content of (Au–Ce vacancy) active sites was estimated by transient analysis of CO oxidation. ► The content of (Au–Ce vacancy) sites correlates with order of activity of studied catalysts. ► Pre-oxidized Au/CeO₂ and Au/Ce–Al samples are more active in CO oxidation than pre-reduced ones.Nanostructured ceria–alumina mixed oxides containing different concentrations of ceria (10 and 30wt.%) were prepared by the sol–gel method using organo-metallic precursors of alumina and ceria. The size of alumina and ceria particles in the prepared Ce–Al–O mixed oxides was smaller than that of pure alumina or ceria. The gold catalysts (3wt.% Au) supported on ceria–alumina mixed oxides by deposition–precipitation (DP) using HAuCl₄ and urea were characterized by several techniques: TEM, XPS and UV–vis spectroscopy, and temperature programmed reduction/oxidation (TPR/TPO). The catalytic activity of prepared Au/CeO₂–Al₂O₃ catalysts in CO oxidation was higher than that of Au/Al₂O₃ and Au/CeO₂ catalysts. Nanostructured ceria incorporated into an alumina matrix has been found quite effective for gold species activation in CO oxidation. In fact, transient analysis of CO oxidation provided an estimate of the relative content of (Au–ceria vacancy) active sites in catalysts. Obtained values are in good agreement with the order of activity for tested samples and gold dispersion according to EXAFS data.

Keywords: Gold; Nanoparticles; Ceria–alumina; Mixed oxides; Sol–gel; Transient analysis

Hydrolysis and thermolysis of urea and its decomposition byproducts biuret, cyanuric acid and melamine over anatase TiO₂ by Andreas M. Bernhard; Daniel Peitz; Martin Elsener; Alexander Wokaun; Oliver Kröcher (pp. 129-137).

Display Omitted► Anatase TiO₂ as hydrolysis catalyst for urea decomposition byproducts. ► Biuret is directly hydrolyzed in one step to urea over TiO₂ at only 100°C. ► Melamine is hydrolyzed in a multi-step reaction, starting at substituting the amine groups. ►Stability against hydrolysis over TiO₂: cyanuric acid>ammeline>ammelide≈melamine.A major problem in the selective catalytic reduction of NO_x with urea (urea-SCR) is the formation of urea decomposition byproducts, which can be suppressed by the use of TiO₂ as a hydrolysis catalyst. Temperature programmed desorption and reaction (TPD/R) experiments with urea, biuret, triuret, cyanuric acid and melamine on TiO₂-coated and inert cordierite monoliths were used to investigate the reaction network of urea byproduct formation and decomposition over anatase TiO₂. All investigated compounds were found to be catalytically hydrolyzed over TiO₂. Biuret was directly hydrolyzed to urea in one step, whereas melamine hydrolyzed step-wise via ammeline and ammelide to cyanuric acid. Finally, cyanuric acid completely hydrolyzed to ammonia and carbon dioxide. The formation of byproducts was strongly favored in the absence of water. A reaction network was developed for the uncatalyzed and catalytic decomposition of urea, showing the most important reactions of urea, isocyanic acid, biuret, triuret, cyanuric acid, ammelide, ammeline and melamine under low-temperature operating conditions in SCR systems. Our results support the approach of using a special hydrolysis catalyst for urea decomposition or of catalytic coatings on exhaust pipes to avoid byproduct formation.

Keywords: Abbreviations; cpsi; cells per square inch; CYA; cyanuric acid; DSC; differential scanning calorimetry; FTIR; Fourier transform infrared; GHSV; gas hourly space velocity; SCR; selective catalytic reduction of NO; _x; STP; standard pressure and temperature for gases (; T; =; 0; °C,; p; =; 1013.25; hPa); TGA; thermogravimetric analysis; TPD/R; temperature programmed desorption and reactionBiuret hydrolysis; Melamine hydrolysis; Anatase TiO; ₂; Urea-SCR; HPLC

Utilization of e-waste as a silica source for the synthesis of the catalyst support MCM-48 and highly enhanced photocatalytic activity of supported titania nanoparticles by Tzong-Horng Liou; Bo-Chen Lai (pp. 138-148).

Pure titania reveals a very weak photocatalytic activity. MCM-48 plays a major role in adsorption of MB. The hybrid catalysts’ higher surface areas and adsorption capacities are significant factors in increased elimination of dye. Titania/MCM-48 has a higher photoefficiency than that of titania/silica-gel.Display Omitted► Synthesis of mesoporous photocatalysts from e-waste. ► Titania/MCM-48 shows a combined effect of photoactivity with high adsorptive efficiency. ► The porosity and adsorption capacity of MCM-48 support is affected by titania ratios. ► Hybrid catalyst material has a high surface area of 1046m²/g. ► Good dispersion of titania on MCM-48 support obtains high photocatalytic efficiency.An extensive range of studies has investigated the silica-supported TiO₂ catalyst. However, research on cubic-type MCM-48 photocatalyst materials is limited. E-waste represents one of the fastest-growing sources of industrial waste worldwide. The present study reports, for the first time, direct synthesis of TiO₂ nanoparticles loaded on MCM-48 deriving from e-waste. Alkali-extracted electronic packaging resin ash provided a source of sodium silicate precursors. Titanium salts were introduced into the pores of MCM-48 and subsequently decomposed to TiO₂ nanoparticles. Methylene blue was used to evaluate the photoactivity of the hybrid catalyst at varying amounts of TiO₂ loading, catalyst masses, and heat-treatment temperatures. Results indicated that TiO₂/MCM-48 demonstrates a combined effect, including the photocatalytic activity of TiO₂ along with the high adsorptive efficiency of MCM-48. Different ratios of titanium metal deposited on silica surfaces had significant influences on the porosity and adsorption properties of the MCM-48 support, as well as the dispersion, particle size, and catalytic activity of the TiO₂ catalyst. Good dispersion of TiO₂ on the MCM-48 support played a significant role in obtaining high photocatalytic activity. Synthesis of mesoporous photocatalysts from e-waste using a green approach can reduce the disposal problem and produce viable materials for a wide range of applications.

Keywords: E-waste; Titania; MCM-48; Photocatalyst; Mesoporous structure

Preparation, characterization and photocatalytic activity of TiO₂–ZrO₂ binary oxide nanoparticles by Ayca Kambur; Gulin Selda Pozan; Ismail Boz (pp. 149-158).

Display Omitted► TiO₂–ZrO₂ binary oxide nanoparticles as a photocatalyst for enhancing of the activity. ► The different catalyst preparation method and morphology effect on the photocatalytic degradation reaction. ► The solid state dispersion for photocatalysis.TiO₂–ZrO₂ binary oxide catalysts were successfully prepared by a solid state reaction. The interaction between TiO₂ and ZrO₂ affected the photocatalytic efficiency of mixture. 50%TiO₂–ZrO₂ photocatalyst exhibited much higher photocatalytic activity than pure TiO₂ and the standard Degussa TiO₂ P-25 in the degradation of phenol under UV irradiation. The profound effect of binary oxide catalyst for phenol degradation is generally considered due to the high surface area, small particle size, anatase phase and high monoclinic phase of ZrO₂ content, and the presence of more surface OH groups than that of the pure TiO₂ and ZrO₂ photocatalyst. A natural pH of 5 is favorable for the photodegradation of phenol by 50TiO₂–ZrO₂ solid state dispersion (SSD) and 90% TOC removal can be achieved in 90min. Monoclinic form of ZrO₂ is found to be more effective for photodegradation. The catalytic activity was affected by the preparation method. The observed photodegradation activity for phenol follows the order 50%TiO₂–ZrO₂ (solid state dispersion) >50%TiO₂–ZrO₂ (impregnation (IMP)) >50%TiO₂–ZrO₂ (sol–gel (SG)).

Keywords: Photocatalysis; Phenol; ZrO; ₂; TiO; ₂; UV irradiation; Characterization

Catalytic steam reforming of biomass tar over iron- or nickel-based catalyst supported on calcined scallop shell by Guoqing Guan; Gang Chen; Yutaka Kasai; Eldin Wee Chuan Lim; Xiaogang Hao; Malinee Kaewpanha; Abudula Abuliti; Chihiro Fushimi; Atsushi Tsutsumi (pp. 159-168).

Display Omitted► Calcined scallop shell was used for adsorption and steam reforming of biomass tar. ► Steam reforming of tar over Fe- or Ni-doped calcined scallop shell was performed. ► Mechanism of metal oxide doped catalysts was investigated.Calcined scallop shell (CS) exhibits alkaline property with a porous structure, and could be applied for the adsorption and decomposition of biomass-derived tar. In this study, steam reforming of tar derived from pruned apple branch over CS was investigated in a fixed bed at 650°C. It was found that CS had good activity for the steam reforming of tar to produce synthesis gas (syngas), and was able to be recycled. To promote the gas production efficiency, iron or nickel was supported on the CS, and used for the reforming of tar. The effect of heating rate on the gas production rate was investigated, and it was found that reduced iron- or nickel-supported CS showed better activities under the condition of rapid heating. Iron- or nickel-based catalyst in its oxide state was also investigated for the reforming of tar. No catalytic activity was found at the beginning, but good activity appeared after approximately 30min of reaction when the metal oxide was reduced to its metallic form by the initially generated syngas (CO and H₂) from the pyrolysis of biomass without the aid of catalyst. Iron and nickel in their metallic forms rather than their oxide ones were considered as active sites for the reforming of tar. Furthermore, the alkaline elements in the biomass, which could enhance the activity of the catalysts, were identified to be accumulated on the surface of the catalysts with the biomass-derived tar. As a result, a larger amount of syngas was produced when the regenerated catalysts were applied. Based on these experimental results, a possible catalytic process was proposed.

Keywords: Biomass; Pruned apple branch; Tar; Catalytic steam reforming; Scallop shell; Iron; Nickel; CaO

Pore size tuning of functionalized SBA-15 catalysts for the selective production of furfural from xylose by I. Agirrezabal-Telleria; J. Requies; M.B. Güemez; P.L. Arias (pp. 169-178).

Display Omitted► Functionalized SBA-15 are promising materials for the dehydration of xylose to furfural. ► Furfural was selectively produced by varying the textural properties of propylsulfonic SBA-15. ► Maximum furfural yield of 82% for materials aged at 100°C and reaction temperature of 170°C. ► Propylsulfonic acid sites show high stability in DMSO but lower in water.Furfural (FUR) is widely used as an industrial solvent and can be potentially used as building-block to produce added-value products, such as methyltetrahydrofuran (MeTHF) or levulinic acid. It is currently manufactured from pentosan-rich biomass via steam-stripping under homogeneously catalyzed conditions. Alternatives focus on novel process optimization or on the design of heterogeneous water-tolerant Brönsted acids. In this work, functionalized SBA-15 catalysts with controlled textural properties were prepared in order to study their performance during xylose cyclodehydration. The combination of these two procedures allowed to selectively produce FUR from xylose. Preliminary catalyst screening at 140°C showed a FUR selectivity maxima for the material aged at 100°C. Moreover, the results revealed a direct influence of the sulfonic load and the reaction temperature on the catalytic performance of SBA-15 samples. Promising results were achieved for the propylsulfonic SBA-15 aged at 100°C, since it could optimize the FUR yield up to 82% at 170°C of reaction temperature. Finally, the stability of the catalysts in different solvents and their regeneration were also evaluated.

Keywords: Furfural; Xylose-dehydration; Functionalized; SBA-15; Aging

The effect of synergy between Cr₂O₃-CeO₂ and USY zeolite on the catalytic performance and durability of chromium and cerium modified USY catalysts for decomposition of chlorinated volatile organic compounds by Qinqin Huang; Zhonghua Meng; Renxian Zhou (pp. 179-189).

Display Omitted► Interaction between Cr₂O₃ and CeO₂ optimizes the acidity distribution over Cr₂O₃-CeO₂-USY. ► Interaction between Cr₂O₃ and CeO₂ improves the mobility of oxygen species in Cr₂O₃-CeO₂-USY. ► Synergy between Cr₂O₃-CeO₂ and USY enhances the catalytic performance for CVOCs destruction. ► Synergy between Cr₂O₃-CeO₂ and USY improves the durability of the catalyst for DCE oxidation.The chromium and cerium modified USY zeolite catalysts (Cr₂O₃-CeO₂-USY) were prepared by impregnation method and investigated in terms of catalytic decomposition of dichloromethane (DCM), trichloroethylene (TCE) and 1,2-dichloroethane (DCE). The results show that there are two types of active sites in the catalysts. The acidic site is the active center for dehydrochlorination of CVOCs, and the metallic xoide is the center providing active oxygen species for CVOCs deeper oxidation. The interaction between Cr₂O₃ and CeO₂ species optimizes the concentration ratio of strong acid sites to weak acid sites and improves the mobility of oxygen species over Cr₂O₃-CeO₂-USY catalysts, which is beneficial to the dehydrochlorination and deeper oxidation of chlorinated volatile organic compounds (CVOCs), respectively. Cr₂O₃-CeO₂-USY catalyst with 17.5wt.% loading of Cr₂O₃ (17.5Cr₂O₃-12.5CeO₂-USY) presents better catalytic performance for CVOCs decomposition along with higher selectivity to HCl and CO₂ formation, which can be due to the higher percentage of strong acidity, more accessible oxygen species, and the stronger synergy between Cr₂O₃-CeO₂ and USY zeolite. In addition, the stronger interaction between Cr₂O₃ and CeO₂, along with the synergy between Cr₂O₃-CeO₂ and USY zeolite over 17.5Cr₂O₃-12.5CeO₂-USY results in less coke deposit, slight HCl attack on the catalysts and improved resistance to chlorination of active components. Therefore, 17.5Cr₂O₃-12.5CeO₂-USY shows the better durability and structure stability during the long term exposure to DCE.

Keywords: Keyword; Cr; ₂; O; ₃; -CeO; ₂; -USY catalysts; CVOCs decomposition; Deeper oxidation ability; Catalytic performance; Durability

Effect of a second metal (Y, K, Ca, Mn or Cu) addition on the carbon dioxide reforming of methane over nanostructured palladium catalysts by Chunkai Shi; Peng Zhang (pp. 190-200).

Y-modified nanostructured Pd/Al₂O₃ catalyst shows the highest initial activity and the best long-term stability with no activity loss for carbon dioxide reforming of methane, owing to its best Pd dispersion, the strongest capability of both metal sintering and coking resistances.Display Omitted► The activity and stability of catalyst depend on its Pd dispersion, metal sintering and carbon resistance. ► Pd/Al₂O₃ has high initial activity but it suffers from very severe carbon deposition and quickly deactivates. ► Pd5Y/Al₂O₃ shows the highest initial activity and the best stability with no activity loss. ► Catalysts with added K, Ca, Mn or Cu additives drop the catalytic activities to different extent after long terms runs. ► The Pd particle size of 10nm is crucial below which carbon formation can be totally avoided.The CO₂ reforming of CH₄ to synthesis gas was investigated over nanostructured Pd/Al₂O₃ catalysts promoted by various additives (K, Ca, Y, Mn and Cu) using a stoichiometric feedstock mixture. In order to understand the effect of the additives on the surface properties and catalytic performance of the catalysts, fresh and spent samples were characterized by a number of techniques, such as N₂ adsorption-desorption isotherms, XRD, CO-chemisorption, H₂-TPR, TPO, Raman and TEM. Additives strongly modified the reduction properties of Pd species and metal surface dispersion. The results showed that the addition of Y or Ca to Pd/Al₂O₃ slightly increased the initial activity expressed as CH₄ and CO₂ conversions, which is attributed to decreased reducibility of Pd species and enhanced Pd dispersion. In contrast, while the addition of K, Mn and Cu similarly reduced the reducibility of Pd species, their surface metal dispersions apparently decreased owing to decoration effect or alloy formation. This leads to lower initial activities for the modified catalysts than Pd/Al₂O₃. On the other hand, stability of catalysts activity during the long-term tests was associated with Pd sintering resistance as well as carbon deposition. The CO₂ reforming of CH₄ was ceased over Pd/Al₂O₃ after around 4.5h of reaction due to catalyst bed blockage caused by the large amount of carbon deposition. The carbon formation was accelerated by Pd sintering. Among all catalysts, Y-modified Pd/Al₂O₃ showed the best stability with almost no activity loss in 20h of reaction. This is probably because that the addition of Y to Pd/Al₂O₃ notably suppresses carbon formation and metal sintering and maintains Pd particle size below 10nm. This particle size is crucial, below which carbon formation can be completely avoided under the present reforming conditions. For catalysts with other additives the catalytic activities decreased to different degrees after long-term tests, due to metal sintering and carbon deposition.

Keywords: CO; ₂; reforming of CH; ₄; Palladium catalysts; Yttrium; Potassium; Calcium; Manganese; Copper; Carbon deposition

High selectivity in visible-light-driven partial photocatalytic oxidation of benzyl alcohol into benzaldehyde over single-crystalline rutile TiO₂ nanorods by Cong-Ju Li; Guo-Rong Xu; Baohong Zhang; Jian Ru Gong (pp. 201-208).

The photocatalytic oxidation of benzyl alcohol into benzaldehyde under visible-light irradiation over single-crystalline rutile TiO₂ nanorods shows high selectivity of over 99%.Display Omitted► Hierarchical structures constituting single-crystalline rutile TiO₂ nanorods were fabricated. ► The obtained samples showed a high selectivity of >99% in the partial photocatalysis. ► The high activity was ascribed to the surface properties and unique characteristics of samples.Selective photocatalysis offers an alternative green approach for valuable fine chemical synthesis and environmental remediation. In this work, high selectivity in visible-light-driven partial photocatalytic oxidation of benzyl alcohol over single-crystalline rutile TiO₂ nanorods was achieved. The nanorods were prepared by a hydrothermal reaction using rutile TiO₂ nanofibers obtained from calcination of composite electrospun nanofibers as a substrate. The selectivity of partial photocatalytic oxidation of benzyl alcohol over the obtained rutile TiO₂ nanorods under visible-light irradiation was over 99%, much better than the results reported over nanoparticle counterparts under UV light irradiation. A tentative reaction mechanism was proposed, that is, benzyl alcohol was first adsorbed on the surface of rutile TiO₂ to form a complex which could absorb visible-light to generate electrons and holes, then was oxidized into the benzaldehyde by electrons transfer and holes-attracted release of H atom. In addition, the unidirectional property of nanorods favored the electron transfer and thus the selectivity. To the best of our knowledge, it is the first report of the rutile TiO₂ nanorods for the visible-light-driven selective photocatalysis. Our work extends the selective photocatalysts to one-dimensional nanomaterials instead of limiting to the commonly used nanoparticles and will open up an intriguing perspective for green synthesis and efficient energy conversion.

Keywords: Selective photocatalysis; Single-crystalline; Rutile TiO; ₂; Benzyl alcohol

A parametric study of the UV-A photocatalytic oxidation of H₂S over TiO₂ by Angela Alonso-Tellez; Didier Robert; Nicolas Keller; Valérie Keller (pp. 209-218).

Display Omitted► A parametric study of the UV-A photocatalytic oxidation of H₂S was performed over TiO₂ P25. ► Reaction pathways and mechanisms were discussed. ► Ti⁴⁺ surface sites were proposed to act as active sites for H₂S oxidation. ► Non-illuminated deepest TiO₂ layers could play a role for enhancing sulfur removal efficiency. ► Weakly basic washing was efficient as regeneration treatment for removing surface sulfates and recovering the TiO₂ activity.A parametric study of the UV-A H₂S photocatalytic oxidation over TiO₂ P25 has investigated the influence of the TiO₂ coating surface density, the total flow rate, the relative humidity, the temperature and the irradiance as main reaction parameters on the H₂S conversion, the SO₂ selectivity (targeted as low as possible), the duration without any SO₂ release, and thus on the gas phase sulfur removal efficiency. The deepest non-illuminated internal TiO₂ layers – even not photocatalytically active – could play a role in adsorbing SO₂ and delaying its release into the gas phase, for explaining the behavior of high surface density TiO₂ coatings. The Ti⁴⁺ surface sites have been proposed to act as active sites for the H₂S photocatalytic oxidation, and general reaction pathways leading to the formation of SO₂ in the gas phase and to surface sulfates have been hypothesized, involving photogenerated holes, sulfhydryl radicals or hydroxyl radicals. The role of active sulfate radicals has been put forward for explaining the behavior turn with time on stream on sulfate-deactivated TiO₂, from a progressive deactivation into a complete H₂S conversion to SO₂. Finally, effective regeneration treatment with recovering of the initial activity could be performed by weakly basic washing.

Keywords: TiO; ₂; Hydrogen sulfide; Photocatalysis; Sulfates; Parametric study; Regeneration; XPS surface analysis; Reaction mechanisms

Synergistic effects of TiO₂ photocatalysis in combination with Fenton-like reactions on oxidation of organic compounds at circumneutral pH by Hyung-Eun Kim; Jaesang Lee; Hongshin Lee; Changha Lee (pp. 219-224).

Display Omitted► The combination of UV/TiO₂ and Fe(III)/H₂O₂ leads to synergistic degradation of contaminants. ► The synergistic effects result from dual roles of iron. Iron facilitates charge separation in TiO₂ photocatalyst. ► Iron on the photoexcited TiO₂ surface does not produce Fe(IV) via the Fenton reaction.The integration of two different AOPs often offers synergistic reaction routes for the production ofOH. In this study, synergistic production ofOH was observed in the combined system of TiO₂ photocatalysis and the Fenton-like reaction, causing a drastic enhancement in the oxidation of organic compounds at circumneutral pH values. The photolytic experiments using organic substrates (i.e., phenol, benzoic acid, and methanol) and valence band hole andOH scavengers (i.e., formate and tert-butyl alcohol) show that the synergistic effects result from dual roles of iron as an electron acceptor to facilitate charge separation in TiO₂ photocatalyst and as a Fenton reagent to catalyze conversion of H₂O₂ intoOH. A noteworthy observation is that the adsorption of iron onto the photoexcited TiO₂ surface possibly modifies electron transfer properties of iron toward H₂O₂ at neutral pH to convert the resultant reactive oxidant from Fe(IV) into a stronger form, likelyOH.

Keywords: Fenton reaction; Titanium dioxide; Photocatalysis; Neutral pH; Hydroxyl radical

Ethanol adsorption and oxidation on bimetallic catalysts containing platinum and base metal oxide supported on MCM-41 by Kamolwan Rintramee; Karin Föttinger; Günther Rupprechter; Jatuporn Wittayakun (pp. 225-235).

Display Omitted► CO₂ was generated from ethanol desorption from Co/MCM-41 and Pt–Co/MCM-41. ► Possible adsorption modes and surface species were proposed. ► Surface species from ethanol oxidation on Pt and Pt–Co catalysts were confirmed. ► The mechanisms of ethanol oxidation were proposed. ► The Pt was more active than the Pt–Co catalyst but seemed to deactivate faster.Ethanol pollutant either emitted from ethanol-fueled vehicles at low temperature or released from industries as volatile organic compound (VOC) could be removed by catalytic oxidation. This work investigated adsorption of ethanol on bimetallic catalysts containing Pt with loading of 0.5wt% and Co, Cu, or Mn with loading of 15wt% supported on RH-MCM-41 by temperature programmed desorption (ethanol-TPD) and thermogravimetric analysis (ethanol-TGA). Evolution of gases from the ethanol-TPD indicated the role of oxides as potential oxygen supplier in ethanol oxidation. On the monometallic catalyst containing oxides of Co, Cu, and Mn on MCM-41, the oxide of Co was the better oxygen supplier than that of the others to react with the adsorbed ethanol to produce CO₂. Furthermore, the bimetallic 0.5Pt–15Co/RH-MCM-41 with cobalt in the form of Co₃O₄, showed the highest ethanol adsorption and CO₂ desorption. Consequently, ethanol oxidation was studied on the bimetallic 0.5Pt–15Co/RH-MCM-41 by in situ infrared spectroscopy in which intermediates and reaction pathways were proposed when ethanol and oxygen were flowed through the cell at various temperatures. Results from the ethanol oxidation in a fixed bed flow reactor showed that the bimetallic catalyst gave lower ethanol conversion than monometallic Pt but seemed to be more stable than the monometallic Pt catalyst.

Keywords: Ethanol adsorption; Ethanol oxidation; Bimetallic catalyst; MCM-41; Platinum; Cobalt

Ethanol supercritical route for fabricating bimodal carbon modified mesoporous TiO₂ with enhanced photocatalytic capability in degrading phenol by Ya Zhang; Peng Zhang; Yuning Huo; Dieqing Zhang; Guisheng Li; Hexing Li (pp. 236-244).

The bimodal carbon modified mesoporous TiO₂ prepared via ethanol supercritical route exhibited an excellent photocatalytic performance for degrading phenol, owing to its strong visible light absorption capability and high electron–hole separation rate.Display Omitted► An effective supercritical fluid based route for fabricating bimodal carbon modified TiO₂. ► Mesoporous structure with large surface area and high crystallinity. ► High photocatalytic performance and stability for degrading phenol under visible light. ► Elucidate the activity contribution from the various carbon modification modals.This paper reports the fabrication of a novel mesoporous C-TiO₂ photocatalyst via an ethanol supercritical solvothermal method involving tetrabutyl titanate and raw rice. Such as-prepared C-TiO₂ possessed a bimodal carbon-modification effect, including carbon doping in the lattice of TiO₂ and carbon sensitizing the surface of TiO₂. The ethanol supercritical treatment also contributed mesoporous structure with large surface area (160m²/g) and high crystallinity of anatase to the C-TiO₂. These materials exhibited an excellent photocatalytic performance and recyclability for phenol oxidation under visible light irradiation ( λ>420nm). The C-TiO₂ samples were characterized by using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed oxidation (TPO), Raman and ultraviolet–visible reflectance (UV–vis) spectroscopy. The relationship between the physicochemical property and the photocatalytic performance of the as prepared samples is discussed. We also investigate the effect of the supercritical temperature and calcining temperature on the photocatalytic performance of the obtained C-TiO₂. The present work explores an effective supercritical fluid based route for the fabrication of mesoporous C-TiO₂ with bimodal carbon modification effect and high photocatalytic performance for treating phenol, which can be extended to synthesize other functional photocatalytic materials.

Keywords: Bimodal carbon-modification; TiO; ₂; Supercritical; Phenol; Photocatalytic

One-pot pyridine-assisted synthesis of visible-light-driven photocatalyst Ag/Ag₃PO₄ by Yongping Liu; Liang Fang; Huidan Lu; Yanwei Li; Changzheng Hu; Huogen Yu (pp. 245-252).

Display Omitted► One-pot pyridine-assisted hydrothermal method to prepare Ag/Ag₃PO₄ photocatalyst. ► Pyridine plays a coordination agent and a reductant for Ag⁺ ions. ► The composite is efficient and stable for methyl orange and phenol photodegradation.A highly efficient and stable Ag/Ag₃PO₄ photocatalyst was prepared by a facile one-pot hydrothermal method assisted by pyridine. Pyridine played two important roles in the synthesis: it could work as a coordination agent role of Ag⁺ and act as reductant for reduce partial Ag⁺ to metallic Ag. The influences of pyridine amount, reaction temperature and pH value on the content of Ag in the composite were investigated. The diffuse reflectance spectra (DRS) indicated that the Ag/Ag₃PO₄ had strong absorption in UV and visible light regions. The photocatalytic activity of the composite was evaluated by the degradation of methyl orange (MO) and phenol under visible light irradiation. The experimental results indicated that the Ag/Ag₃PO₄ showed highly efficient and stable photocatalytic activity under visible light irradiation. It was considered that the excellent performance resulted from the surface plasmon resonance of Ag nanoparticles and a large negative charge of PO₄³⁻ ion.

Keywords: Plasmonic; Photocatalytic; Silver orthophosphate; Hydrothermal; Pyridine

Improving the visible light photocatalytic activity of nano-sized titanium dioxide via the synergistic effects between sulfur doping and sulfation by Yuxiao Niu; Mingyang Xing; Baozhu Tian; Jinlong Zhang (pp. 253-260).

.Display Omitted► S doped and sulfated TiO₂ photocatalysts were prepared by a low-temperature solvothermal method, with potassium persulfate as sulfur source. ► The S doped and sulfated TiO₂ photocatalysts have high photocatalytic activity to phenol degradation. ► Sulfur can not only be doped into TiO₂ lattice but also anchored on the surface. ► The high photocatalytic activity of phenol was caused by the synergistic effect between S doping and sulfation.S-doped and sulfated nano-sized TiO₂ photocatalysts were prepared by a low-temperature solvothermal method, using potassium persulfate as sulfur source. The obtained samples were characterized by XRD, UV–vis DRS, FTIR, FTIR-pyridine, XPS, and nitrogen adsorption–desorption methods. Compared with undoped TiO₂, the S-doped and sulfated TiO₂ photocatalysts exhibited much higher photocatalytic activity for phenol degradation under visible light irradiation. It was revealed that S was not only incorporated into the crystal lattice of TiO₂ replacing Ti⁴⁺ (as S⁴⁺) but also anchored on its surface in the form of SO₄²⁻. Further study indicated that there are synergistic effects between doped S and anchored SO₄²⁻ on improving the visible light photocatalytic activity of TiO₂. The doped S can form an impurity level below the conduction band of TiO₂, extending the light response of TiO₂ into visible light region, while SO₄²⁻ anchored on TiO₂ surface is favorable for trapping photo-induced electrons, suppressing the recombination of electrons and holes and consequently promoting the formation of hydroxyl radical.

Keywords: Potassium persulfate; Synergistic action; Sulfur doping; SO; ₄; ²⁻; Phenol degradation

Hypercrosslinked polystyrene sulphonic acid catalysts for the esterification of free fatty acids in biodiesel synthesis by E. Andrijanto; E.A. Dawson; D.R. Brown (pp. 261-268).

Display Omitted► Hypercrosslinked polystyrene sulphonic acid resins are active solid acid catalysts. ► Highly accessible acid sites on hypercrosslinked polystyrene sulphonic acid resins. ► New solid acid catalysts for free fatty acid esterification in biodiesel synthesis.New sulphonic acid catalysts supported on hypercrosslinked polystyrene have been studied in the esterification of oleic acid with methanol and in the rearrangement of α-pinene to camphene and limonenes. The catalysts have been characterised in terms of specific surface areas and porosities, affinities for water and for cylcohexane vapours, and both concentrations and strengths of acid sites. They have been compared with conventional macroporous polystyrene sulphonic acids (Amberlysts 15 and 35) and SAC-13, a composite between Nafion and silica. The results show that the hypercrosslinked polystyrene sulphonic acids, despite exhibiting relatively low concentrations of acid sites and acid site strengths below those of Amberlysts 15 and 35, are very much more catalytically active than conventional resins in reactions such as the esterification in which high acid site strengths are not required. It is thought that this is due to the highly accessible acid sites throughout the catalyst particles. Reusability studies are reported and it appears that the temperature at which the catalyst is used is important in controlling and minimising catalyst deactivation.

Keywords: Polystyrene; Sulphonic acid; Hypercrosslinked; Free fatty acids; Catalysis; Biodiesel

Enhanced oxygen reduction activity and durability of Pt catalysts supported on carbon nanofibers by David Sebastián; Andrés García Ruíz; Isabel Suelves; Rafael Moliner; María Jesús Lázaro; Vincenzo Baglio; Alessandro Stassi; Antonino Salvatore Aricò (pp. 269-275).

Display Omitted► Crystallinity, porosity and morphology of various CNF affect the catalytic behavior. ► Using CNF as support enhances the performance with respect to conventional support. ► Maximum mass activity is achieved by a certain proper combination of properties. ► The high graphicity index of CNF reduces carbon corrosion at elevated potential.Carbon nanofibers (CNF) characterized by different mean diameter, BET surface area and graphicity were prepared and used as supports to enhance Pt dispersion in low temperature fuel cell catalyst. As a comparison, a conventional Pt on carbon black (Vulcan XC72R) catalyst was prepared using the same procedure. The most appropriate Pt dispersion was achieved for the carbon nanofiber support showing the best compromise in terms of BET surface area and graphicity. This catalyst shows enhanced electrochemical active surface area (ECSA) and performance for the oxygen reduction reaction (ORR) with respect to the Pt/Vulcan catalyst. A cross-analysis of the supports physical-chemical properties, ECSA and mass activity for the ORR suggests that both Pt dispersion and electronic properties as determined by the effect of surface groups and graphicity play a significant role in determining the electrocatalytic activity. Whereas, regarding the decay associated to the corrosion in accelerated degradation tests (ADT), two mitigation effects are envisaged, anchoring effect of surface groups stabilizes Pt nanoparticles with respect to dissolution, whereas a high surface graphicity index reduces carbon corrosion which acts as support for the Pt particles.

Keywords: Pt catalyst; Carbon nanofibers; Fuel cell; Oxygen reduction; Durability

Photocatalytic degradation of Rhodamine 6G on mesoporous titania films: Combined effect of texture and dye aggregation forms by M.N. Ghazzal; H. Kebaili; M. Joseph; D.P. Debecker; P. Eloy; J. De Coninck; E.M. Gaigneaux (pp. 276-284).

Display Omitted► The morphologies of variable TiO₂ films were obtained using different templates. ► The form of the Rhodamine 6G aggregation depends on the surface morphology. ► Photocatalytic degradation of monomer form occurs faster than dimer form. ► Kinetic degradation of Rhodamine 6G depends on the film texture and the aggregation form.Titania films with different textural properties have been synthesized using the sol–gel spin-coating process. Titania sols were prepared with and without non ionic template agents, Pluronic^® P123 and Brij56^®, in order to evaluate the effect of the surface developed by the films on their photocatalytic activity. The morphology, surface composition, open porosity and pore size distribution of these films were investigated by transmission electronic microscopy, X-ray photoelectron spectroscopy and atmospheric ellipsometric porosimetry. The optical properties of the titania films were evaluated by UV–vis transmittance spectroscopy. The porosity released after burning the template at 400°C reduces the refractive index of the coatings and the transmittance in the visible range becomes equal for naked and coated soda lime glasses. In parallel, the photocatalytic activity of the non porous and porous titania films was evaluated by following the photodegradation kinetics of Rhodamine 6G dye. Results show that the increase of the available active surface of the titania films affects the photocatalytic activity. However, this feature was not the only parameter responsible for the improvement of the photocatalytic efficiency. The aggregation form of the Rhodamine 6G dye was also related to titania film texture. This proved to have a marked impact on the photocatalytic performances.

Keywords: Mesoporous film; TiO; ₂; Photocatalysis; Dye aggregation; Rhodamine 6G

Degradation intermediates and reaction pathway of pyraclostrobin with TiO₂ photocatalysis by Laura Lagunas-Allué; María-Teresa Martínez-Soria; Jesús Sanz-Asensio; Arnaud Salvador; Corinne Ferronato; Jean Marc Chovelon (pp. 285-293).

Display Omitted► Pyraclostrobin was totally degraded in an aqueous TiO₂ suspension in the dark after 60min. ► The rate constant for the reaction of pyraclostrobin was calculated as k_obs=1.4×10⁻²min⁻¹. ► The photodegradation rate was found to increase along with decreasing pH. ► Eleven intermediates were identified by HPLC–APCI–MS/MS. ► A mechanism of degradation has been tentatively proposed.The present study deals with the photocatalytic degradation of the strobilurin pyraclostrobin in the presence of titanium dioxide (TiO₂) as a photocatalyst and UV light irradiation. The obtained results show a complete degradation of pyraclostrobin at pH 6.2, temperature at 20±1°C and 0.5gL⁻¹ of catalyst after 60min irradiation. Photodegradation of pyraclostrobin exhibited pseudo-first-order reaction kinetics. The rate of photodecomposition of pyraclostrobin was measured using high performance liquid chromatography–diode array detector (HPLC–DAD). The effect of solution pH in the 2–10 range was investigated as well as the reaction intermediates formed during degradation. To obtain a better understanding of the mechanistic details of this TiO₂-assisted photodegradation of pyraclostrobin with UV-irradiation, the intermediates of the processes were concentrated, separated and identified by the solid-phase extraction (SPE) and liquid chromatography/mass spectrometry (LC–MS/MS) technique. The probable photodegradation pathways were proposed and discussed. The main steps involved: hydroxylation of the aromatic rings (chloro-phenyl, phenyl and pyrazol) followed by the loss of the N-methoxy group, substitution of chloride atom by a hydroxyl group, rupture of the pyrazol and phenyl bond and the scission of the oxygen and pyrazol bond.

Keywords: Pyraclostrobin degradation; Photocatalysis; TiO; ₂; Intermediate products; HPLC–MS/MS

Gold nanoparticles on titanium oxide effective for photocatalytic hydrogen formation under visible light by Hayato Yuzawa; Tomoko Yoshida; Hisao Yoshida (pp. 294-302).

.Display Omitted► We prepared various Au/TiO₂ samples, plasmonic photocatalyst, by two methods. ► We studied H₂ formation from EtOH over the Au/TiO₂ under visible light in detail. ► Au/TiO₂ constantly promoted H₂ production through the LSPR of Au. ► Short rod-like Au nanoparticles were more effective than spherical ones for the reaction. ► Anatase TiO₂ with large particle size was effective for the photocatalysis.Photocatalytic hydrogen production from aqueous ethanol was investigated over Au-loaded titanium oxide under visible light (510–740nm) irradiation. Hydrogen was constantly produced through the present plasmonic photocatalysis. In this system, Au nanoparticles with larger particle size were essentially effective for the reaction due to the high efficiency for the localized surface plasmon resonance (LSPR). Further, Au nanoparticles with short rod-like shapes were more effective for the reaction than those with spherical shape because of the higher efficiency for the electron transfer from the Au nanoparticle to the conduction band of titanium oxide. On the other hand, aggregates of the Au nanoparticles were not appropriate for the reaction, which derived from the low efficiency of the electron transfer. Finally, titanium oxide containing anatase phase with larger particle size was most preferred for the reaction.

Keywords: Plasmonic photocatalysis; Visible light; Hydrogen formation; Au nanoparticles; Titanium oxide

Template-free synthesis of polymer-derived mesoporous SiOC/TiO₂ and SiOC/N-doped TiO₂ ceramic composites for application in the removal of organic dyes from contaminated water by Mirabbos Hojamberdiev; Ravi Mohan Prasad; Koji Morita; Yongfa Zhu; Marco Antônio Schiavon; Aleksander Gurlo; Ralf Riedel (pp. 303-313).

Display Omitted► Microporous SiOC ceramic transforms to mesoporous ceramic composites. ► TiO₂ and N-doped TiO₂ particles are homogenously distributed in the SiOC matrices. ► Anatase-to-rutile transformation is delayed in the SiOC/N-doped TiO₂ composite. ► SiOC/N-doped TiO₂ composite shows lower S_BET values compared to SiOC/TiO₂ composite. ► N-doped TiO₂-containing composite presents the highest photocatalytic activity.Mesoporous SiOC/TiO₂ and SiOC/N-doped TiO₂ (nitrogen-doped TiO₂) ceramic composites were prepared by the incorporation of TiO₂ (containing 65wt.% anatase and 35wt.% rutile) and N-doped TiO₂ powders into vinyl-functionalized polysiloxane polymer followed by pyrolysis at 700–900°C for 2h in argon atmosphere. The N-doped TiO₂ powders were obtained by ammonolysis of commercial TiO₂ nanopowders. The resulting samples were characterized by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and nitrogen physisorption. The specific surface area ( S_BET) values of the as-prepared SiOC ceramic and SiOC/TiO₂ and SiOC/N-doped TiO₂ ceramic composites decreased with increasing the pyrolysis temperature due to a gradual collapse of small pores. A transformation from microporous SiOC ceramic (pore-size <2nm) to mesoporous SiOC/TiO₂ and SiOC/N-doped TiO₂ ceramic composites (pore-size ∼4nm) was analyzed. Adsorption and photocatalytic activity of the resulting samples were evaluated by measuring the decrease in concentration of methylene blue (MB) after adsorption in the dark and photodegradation reaction under UV–vis light irradiation, respectively. Pure microporous SiOC ceramic showed no significant adsorption as well as photocatalytic activity for MB because of its high microporosity and low solid acidity, respectively, whereas mesoporous SiOC/TiO₂ and SiOC/N-doped TiO₂ ceramic composites exhibited higher adsorption and photocatalytic activities. The photodegradation rate constant k(×10⁻³min⁻¹) of the samples increased in the following order: 1.3 for SiOC ceramic <2.2 for SiOC/TiO₂ <3.4 for SiOC/N-doped TiO₂. The highest k for the SiOC/N-doped TiO₂ ceramic composite is discussed in terms of the change of the electronic structures and crystallinity of N-doped TiO₂ if compared with pure TiO₂. These polymer-derived ceramic composites can be applied for the purification of water contaminated with organic dyes without the need for hydrogen peroxide.

Keywords: Polymer-derived ceramics; SiOC matrix; Titania; Ceramic composite; Photocatalyst; Nitrogen doping; UV–vis light irradiation

Influence of OH-related defects on the performances of BiPO₄ photocatalyst for the degradation of rhodamine B by Chengsi Pan; Jing Xu; Yi Chen; Yongfa Zhu (pp. 314-319).

Display Omitted► The photocatalytic activity of BiPO₄(72h) for RhB is as twice as that of P25. ► The OH-related defects in BiPO₄ influence photocatalytic activities, obviously. ► The OH-related defects also influence degradation process of RhB. ► BiPO₄ is a representative example for common influences of OH-related defects.BiPO₄ photocatalysts with different concentration of OH-related defects were synthesized for various hydrothermal time. The influence of the OH groups on photocatalytic activity, mineralization and degradation process of RhB was discussed in detail excluding other factors such as BET surface area and nanostructures. The defects in the lattice were observed to noticeably decrease the photocatalytic activity by forming defect levels and recombination centers. These defect levels would limit the transfer of the carriers to produce hydroxyl and super oxide radicals. Furthermore, the deethylation intermediates like N, N, N₀-triethyl rhodamine and N, N₀-diethyl rhodamine were found to accumulate in the solution when large quantities of OH-related defects were in the BiPO₄ lattice. While the cleavage of the whole chromophore occurred when small quantities of OH-related defects were in the BiPO₄ lattice. The reduction of super oxide radicals influenced by the existence of defects was demonstrated to be good for deethylation process and thus resulted in a decrease of the mineralization degree.

Keywords: BiPO; ₄; OH-related defects; Photocatalyst

Current research on thermochemical conversion of biomass at the National Renewable Energy Laboratory by Robert M. Baldwin; Kimberly A. Magrini-Bair; Mark R. Nimlos; Perrine Pepiot; Bryon S. Donohoe; Jesse E. Hensley; Steven D. Phillips (pp. 320-329).

Display Omitted► Novel tar and light hydrocarbon reforming catalyst developed. ► Catalyst is robust and can be used in a recirculating/regenerating reactor configuration with low attrition rates. ► Catalyst has demonstrated excellent tar (>99%) and methane (>90%) conversion efficiency on both model and biomass-derived syngas streams. ► Tar mitigation or elimination during biomass gasification may be used to reduce tar loads on the reformer catalyst impacting overall process economics.The thermochemical research platform at the National Bioenergy Center, National Renewable Energy Laboratory (NREL) is primarily focused on conversion of biomass to transportation fuels using non-biological techniques. Research is conducted in three general areas relating to fuels synthesis via thermochemical conversion by gasification:(1)Biomass gasification fundamentals; chemistry and mechanisms of tar formation(2)Catalytic tar reforming and syngas cleaning(3)Syngas conversion to mixed alcoholsIn addition, the platform supports activities in both technoeconomic analysis (TEA) and life cycle assessment (LCA) of thermochemical conversion processes. Results from the TEA and LCA are used to inform and guide laboratory research for alternative biomass-to-fuels strategies. Detailed process models are developed using the best available material and energy balance information and unit operations models created at NREL and elsewhere. These models are used to identify cost drivers which then form the basis for research programs aimed at reducing costs and improving process efficiency while maintaining sustainability and an overall net reduction in greenhouse gases.

Keywords: Biomass; Thermochemical conversion; Gasification

Band structure controls of SrTiO₃ towards two-step overall water splitting by Shoichi Hara; Hiroshi Irie (pp. 330-335).

Display Omitted► We establish a novel two-step overall water-splitting system. ► The system is composed of two types of SrTiO₃-based photocatalysts. ► The band structure of SrTiO₃ was controlled, producing two types of SrTiO₃. ► The system simultaneously evolves H₂ and O₂ with the aid of I⁻ irradiated with light.We prepared two types of SrTiO₃-based photocatalyst powders, Bi,Ga-doped SrTiO₃ and In,V-doped SrTiO₃. UV–visible reflectance spectra of these powders indicated that their band-gaps remained constant in comparison with that of SrTiO₃. In conjunction with the reported band structure control of oxides, our results indicated that Bi,Ga-doped SrTiO₃ and In,V-doped SrTiO₃ formed isolated mini-bands composed of Bi 6s orbitals in the forbidden band above the valence band, composed of O 2p, and V 3d orbitals below the conduction band, composed of Ti 3d, resulting in the observed visible-light absorption. Utilizing the prepared SrTiO₃-based photocatalysts, we established a two-step overall water-splitting system, in which simultaneous liberation of hydrogen and oxygen with a molar ratio of ∼2:1 was observed in the presence of I⁻ (NaI) under irradiation with UV-containing light. Moreover, visible light contributed the cycling of I⁻/IO₃⁻ redox mediators, resulting in enhanced hydrogen and oxygen liberation when compared to irradiation with UV light alone.

Keywords: Hydrogen; Oxygen; Photocatalysis; Sacrificial agent; Light

Efficiency and reactivity pattern of ceria-based noble metal and transition metal-oxide catalysts in the wet air oxidation of phenol by Francesco Arena; Cristina Italiano; Lorenzo Spadaro (pp. 336-345).

Comparison of the CWAO pattern of the Pt/CeO₂ and MnCeO_x catalysts at 150°C and various catalyst-to-phenol weight ratio ( R) with that of homogeneous systems : TOC vs. phenol conversion.Display Omitted► The activity pattern of Pt/CeO₂ and MnCeO_x systems in the phenol CWAO is addressed. ► Activity pattern is explained by a L–H path based on adsorption and oxidation steps. ► Homogeneous and heterogeneous CWAO processes show diverse phenol-TOC conversion relationships. ► Higher adsorption and oxidation rates explain the better activity of MnCeO_x system.The activity-stability pattern of ceria-based noble metal (Pt/CeO₂) and transition metal-oxide (MnCeO_x) catalysts in the wet air oxidation of phenol (CWAO) at different catalyst-to-phenol weight ratio ( R, 1–5) was comparatively probed using a stirred batch reactor with continuous oxygen feed ( T_R, 150°C;PO2, 0.9MPa). Both Pt/CeO₂ and MnCeO_x systems drive a surface dual-site Langmuir–Hinshelwood (L–H) reaction path enabling higher efficiency, different reaction kinetics and “phenol-total organic carbon” conversion relationships in comparison to homogeneous CWAO catalysts . A simplified reaction scheme based on consecutive adsorption and mineralization steps and the relative kinetic analysis show that the former determines the rate of phenol and TOC removal, while the latter controls the selectivity and rate of catalyst fouling. The MnCeO_x system ensures a fast and complete phenol conversion and a TOC removal higher than 80% at any R, while improved adsorption and mineralization functionalities explain a higher resistance to deactivation by fouling than Pt/CeO₂ system.

Keywords: Abbreviations; R; catalyst-to-phenol weight ratio; k; _Ph; pseudo 1st-order kinetic constant of phenol concentration decay (h; ⁻¹; ); k; CO; 2; pseudo 1st-order kinetic constant of CO; ₂; formation (h; ⁻¹; ); rate; _Ph; rate of phenol concentration decay (mol; L; ⁻¹; h; ⁻¹; ); k; _ads; pseudo 1st-order catalytic constant of phenol adsorption (; k; _ads; =; k; _Ph; /; C; _cat; , L; g; _cat; ⁻¹; h; ⁻¹; ); k; _ox; pseudo 1st-order catalytic constant of phenol oxidation; (; k; ox; =; k; CO; 2; /; C; cat; ,; L; g; cat; −; 1; h; −; 1; ); SSA; _ads; specific surface rate of phenol adsorption (mol; m; _cat; ⁻²; h; ⁻¹; ); SAC; surface adsorption capacity (g; _Ph; m; _cat; ⁻²; )Catalytic wet air oxidation (CWAO); Phenol; Transition-metal oxide catalysts; Noble-metal catalysts; Activity; Selectivity; Stability; Reaction mechanism; Kinetics

Redox stability and electrochemical study of nickel doped chromites as anodes for H₂/CH₄-fueled solid oxide fuel cells by Vicente B. Vert; Francisco V. Melo; Laura Navarrete; José M. Serra (pp. 346-356).

Display Omitted► Catalysts including La1−_xSr_xCr1−_yNi_yO3−_δ ( x=0, 0.15; y=0.05, 0.1, 0.2) were prepared and tested. ► The electrochemical test (EIS) anode was done using both H₂ and CH₄ as fuels on YSZ electrolyte. ► Structural and redox evolution was monitored by XRD, TEM and XPS in oxidized and reduced samples. ► Upon reduction the perovskite structure is kept and metallic nickel nanoparticles are formed.The influence of nickel and strontium incorporation in LaCrO₃ on the crystalline structure, redox behavior and electrochemical performance by impedance spectroscopy using symmetrical cells has been studied. Namely, the La1−_xSr_xCr1−_yNi_yO3−_δ ( x=0, 0.15; y=0.05, 0.1, 0.2) system was investigated. Structural and redox evolution has been monitored by X-ray diffraction in oxidized and reduced samples. Reduced samples kept the initial perovskite structure although metallic nickel nanoparticles were detected on the perovskite grain surface by TEM analysis. The re-oxidized surface did not present nickel particles, suggesting the nickel re-incorporation into perovskite lattice coupled with cation diffusion. The perovskites were tested as SOFC anodes and the polarization resistance depended on the nickel stoichiometry and the reduction temperature. La_0.85Sr_0.15Cr_0.9Ni_0.1O3−_δ reduced at 800°C showed the lowest polarization resistance, both in hydrogen and methane. In fact this composition showed a 20% methane conversion at 900°C for the methane steam reforming in a fixed bed reactor. Tolerance to redox cycling was proved electrochemically by in situ treatments of La_0.85Sr_0.15Cr_0.9Ni_0.1O3−_δ electrode. Materials were further analyzed by TPR and XPS (in oxidized and reduced state) in order to identify the possible species involved in the electrocatalytic processes.

Keywords: Anode; Chromites; Redox cycle; Nickel; Nanoparticle; Redox cycling; Methane steam reforming

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Applied Catalysis B, Environmental (v.115-116, #)