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Applied Catalysis B, Environmental (v.102, #3-4)

Contents (pp. co4).

Editorial Board (pp. co2).

Editorial Board (pp. i).

Contents Continued (pp. i).

NOx removal efficiency and ammonia selectivity during the NOx storage-reduction process over Pt/BaO(Fe, Mn, Ce)/Al₂O₃ model catalysts. Part I: Influence of Fe and Mn addition by N. Le Phuc; X. Courtois; F. Can; S. Royer; P. Marecot; D. Duprez (pp. 353-361).

Display Omitted▶ NOx storage-reduction over Pt/Ba(Fe, Mn)/Al catalysts. ▶ NH₃ selectivity depends on the H₂ conversion introduced during the rich pulses. ▶ The in situ produced NH₃ can react with the stored NOx over Pt/Ba(Mn)/Al. ▶ Mn addition improves the NH₃+NOx reaction at 400°C. ▶ Fe addition induces a catalyst deactivation.NOx storage-reduction process was studied using lean/rich cycling condition over Pt/BaO/Al₂O₃ model catalyst, with a special attention to the ammonia emission. The NOx reduction selectivity strongly depends on the hydrogen conversion introduced during the rich pulses. NH₃ is emitted while hydrogen is not fully converted. It was concluded that the NH₃ formation rate via the NOx reduction by H₂, is higher than the NH₃ reaction rate with NOx to form N₂. The effect of H₂O and CO₂ on the reduction step was also examined and results were explained mainly taking into account the reverse water gas shift reaction.Fe addition in Pt/BaO/Al₂O₃ leads to a strong deactivation of the catalyst, probably due to interaction between iron and platinum. Mn is a poison for the reduction step at 200 and 300°C, but it significantly enhances the NOx reduction at 400°C (conversion and selectivity). Mn favors the NOx reduction with ammonia, even if the introduced hydrogen is not fully converted.

Keywords: NOx storage; NOx reduction; Ammonia; Barium; Lean/rich cycles; Manganese; Iron

NOx removal efficiency and ammonia selectivity during the NOx storage-reduction process over Pt/BaO(Fe, Mn, Ce)/Al₂O₃ model catalysts. Part II: Influence of Ce and Mn–Ce addition by N. Le Phuc; X. Courtois; F. Can; S. Royer; P. Marecot; D. Duprez (pp. 362-371).

Display Omitted► Mn addition to Pt/20Ba/Al improves the NOx reduction only at 400°C. ► Ce addition to Pt/20Ba/Al improves the NOx reduction from 300°C. ► Enhancement is attributed to the improvement of NOx+NH₃ reaction for Mn and Ce. ► Ce also favors the NH₃ oxidation into N₂ via its available oxygen. ► A synergetic effect was observed between Mn and Ce in Pt/20BaMnCe/Al catalysts.It was previously demonstrated in the first part of this work that NOx storage-reduction process over Pt/BaO/Al₂O₃ model catalyst is limited by the reduction step, with ammonia emission since H₂ is not fully consumed. The stored NOx reacts preferentially with the introduced H₂ giving NH₃, than with NH₃ in order to produce N₂. Mn addition favors the NOx reduction with ammonia leading to better conversion and selectivity, but only at 400°C. In Part II, a special attention was focused on the role of Ce and Mn–Ce addition in regard to the NOx conversion and the ammonia emission in the 200–400°C temperature range. With ceria modified Pt/20Ba/Al catalyst, significant improvements are obtained from 300°C. In addition to the enhancement of the NOx+NH₃ reaction, the ammonia selectivity is maintained at a lower level compared with Pt/Ba(Mn)/Al catalysts, even in the case of a large H₂ excess. It is attributed to the ammonia oxidation into N₂ via the available oxygen at the catalyst surface. A synergetic effect is observed between Mn and Ce when they are added simultaneously in Pt/Ba/Al catalyst.

Keywords: NOx storage; NOx reduction; Ammonia; Barium; Lean/rich cycles; Manganese; Ceria

Self-assembly of Pt nanoparticles on highly graphitized carbon nanotubes as an excellent oxygen-reduction catalyst by Sheng Zhang; Yuyan Shao; Geping Yin; Yuehe Lin (pp. 372-377).

Display Omitted▶ Poly(diallyldimethylammonium chloride) noncovalently functionalizes graphitic carbon nanotubes (GCNTs). ▶ Pt nanoparticles are deposited on the surface of GCNTs by self-assembly. ▶ Pt/GCNTs exhibit significantly improved oxygen reduction reaction activity. ▶ This provides a facile route to obtain high performance fuel cell eletrocatalysts.Platinum nanoparticles/graphitic carbon nanotubes (GCNTs) nanocomposites are fabricated with electrostatic self-assembly technology. Pt precursors are uniformly distributed on poly(diallyldimethylammonium chloride)-functionalized GCNTs surface (PDDA-GCNTs) via the electrostatic interaction and then in situ reduced to Pt nanoparticles in ethylene glycol, where PDDA is not only used as the wrapping polymer for GCNTs to preserve the integrity and the electronic structure of GCNTs, but also facilitates the uniform distribution of Pt nanoparticles on the surface of GCNTs. X-ray diffraction patterns and transmission electron microscope images reveal that Pt nanoparticles with an average size of ∼2.7nm are uniformly dispersed on highly graphitized GCNTs. Significant enhancement in the electrocatalytic activity on Pt/PDDA-GCNTs catalyst towards oxygen reduction reaction (ORR) has been demonstrated. In addition, this catalyst also shows enhanced electrochemical durability due to the high graphitization degree of GCNTs. This provides a facile and eco-friendly approach to large-scale production of high performance fuel cell eletrocatalysts.

Keywords: Fuel cells; Graphitized carbon nanotubes; Electrocatalyst; Oxygen reduction; Durability; Self-assembly

Mineralization of antibiotic sulfamethoxazole by photoelectro-Fenton treatment using activated carbon fiber cathode and under UVA irradiation by Aimin Wang; Yu-You Li; Adriana Ledezma Estrada (pp. 378-386).

Display Omitted▶ High efficient photoelectro-Fenton process using activated carbon fiber cathode was developed. ▶ Rapid electrogeneration of H₂O₂ and complete mineralization of antibiotic sulfamethoxazole were achieved. ▶ Aromatic intermediates and carboxylic acids generated, as well as inorganic end product were measured. ▶ A comprehensive SMX degradation pathway involvingOH and UVA is proposed.The mineralization of antibiotic sulfamethoxazole (SMX) of concentrations up to 300mgL⁻¹ was examined by photoelectro-Fenton (PEF) using an activated carbon fiber (ACF) cathode with UVA (365nm) irradiation. Comparative mineralization has been studied by different methods: RuO₂/Ti anodic oxidation (AO), AO in the presence of electrogenerated H₂O₂ (AO-H₂O₂), AO-H₂O₂ in the presence of UVA (AO-H₂O₂-UVA), and both the electro-Fenton (EF) and PEF processes. PEF treatment at a low applied current of 0.36A yields a faster and more complete depollution with 80% of the TOC removed after 6h of electrolysis. The higher oxidative ability of the PEF process can be attributed to the additional hydroxyl radicals (OH) produced by the photo-Fenton reaction. The 63% mineralization in the case of EF treatment was due to the formation of short intermediates, such as carboxylic acids, which were difficult to oxidise withOH. In the AO-H₂O₂-UVA process, about 36% of the TOC was removed after 6h electrolysis, while 28% of the TOC was removed in the AO-H₂O₂ process. SMX is only slightly mineralized by the AO process, with only 25% of the TOC removed. HPLC–MS analysis allowed for up to six aromatic reaction products to be identified during the SMX degradation in the PEF process, mainly formed from the hydroxylation of the aromatic ring or/and isoxazole ring, accompanied by the substitution of the amine group (on aromatic cycle) or methyl group (on isoxazole ring) byOH. The carboxylic acids generated, including oxalic, maleic, oxamic, formic and acetic acids, were detected by ion-exclusion chromatography. The initial organic nitrogen was mainly converted into NH₄⁺ along with a very small proportion of NO₃⁻ ion. Considering all the oxidation intermediates and end products for SMX degradation in the PEF process, a general mineralization mechanism byOH and UVA was proposed.

Keywords: Sulfamethoxazole; Photoelectro-Fenton; Activated carbon fiber cathode; Mineralization

The role of H₂O and oxidized copper species in methanol steam reforming on a Cu/CeO₂/Al₂O₃ catalyst prepared by one-pot sol–gel method by Maria Turco; Giovanni Bagnasco; Claudia Cammarano; Luca Micoli; Maurizio Lenarda; Elisa Moretti; Loretta Storaro; Aldo Talon (pp. 387-394).

Display Omitted▶ Treating a Cu/CeO₂/Al₂O₃ catalyst with H₂O at 250°C oxidizes Cu superficially. ▶ The H₂O oxidized catalyst reacts with CH₃OH at 200–300°C producing CO₂ and H₂. ▶ After SRM test, Cu average oxidation state of 0.45 is measured. ▶ The catalyst is more active and selective for SRM after pre-reduction with H₂.A Cu/CeO₂/Al₂O₃ catalyst prepared by a single-step sol–gel method was studied for methanol steam reforming (SRM) to gain information on the oxidation state of Cu and the role of oxidized Cu species. The catalyst was tested in a new laboratory-made flow apparatus that allowed on-line analysis of the products and measurement of the oxidation state and dispersion of Cu in situ. The catalyst pre-reduced in H₂ was more active and selective than the not pre-reduced one. The oxidation state, evaluated after SRM tests, suggested the presence of a layer of oxygen atoms on the metallic Cu surface. Treating the pre-reduced catalyst with H₂O vapour at 250°C caused dissociative H₂O chemisorption and led to a partial oxidation of Cu. The H₂O oxidized sample reacted with CH₃OH producing CO₂ and H₂ as long as oxygen was present on the Cu surface. The results support an oxidation–reduction mechanism.

Keywords: Methanol steam reforming; Cu/CeO; ₂; /Al; ₂; O; ₃; catalysts; H; ₂; O adsorption; Cu oxidation; One-pot sol–gel method

Oxidation of dichloromethane and perchloroethylene as single compounds and in mixtures by Satu Pitkäaho; Satu Ojala; Teuvo Maunula; Auli Savimäki; Toni Kinnunen; Riitta L. Keiski (pp. 395-403).

Display Omitted▶ Pd-containing catalysts are more active in PCE oxidation than Pt. ▶ The addition of V₂O₅ improves the activity and selectivity of the studied catalysts. ▶ DMF enhances but oxitol and ethanol decrease the conversion of DCM. ▶ PCE oxidation is not affected by additional compounds tested in this study. ▶ Based on the results two industrial catalysts were developed for CVOC elimination.Catalytic oxidation of dichloromethane (DCM) and perchloroethylene (PCE) over different alumina supported noble metal catalysts in moist conditions was studied. Two component mixture tests with dimethylformamide (DMF), oxitol (EGEE), ethanol and ethylene were also performed. DCM and PCE were more difficult to oxidize than DMF and EGEE, the light-off temperature ( T₅₀) of DCM and PCE was 280°C and 482°C, respectively. In general, the addition of V₂O₅ improved the activity and selectivity of the studied catalysts over the oxidation of both chlorinated VOCs. In DCM oxidation Pt catalysts were more active than Pd-containing catalysts, contrary to PCE oxidation where Pd-containing catalysts were more active. The presence of DMF enhanced the DCM conversion decreasing the T₅₀ value by ∼130°C. The presence of both oxitol and ethanol lowered the conversion of DCM. Removing the water feed from the inlet affected the conversion of DCM only a little but on the yield of HCl it had a major effect. In PCE oxidation the impact of additional compounds tested in this study was minor.

Keywords: DCM; PCE; DMF; EGEE; Vanadium; VOC abatement; Chlorinated volatile organic compounds

Rigorous kinetic modelling with explicit radiation absorption effects of the photocatalytic inactivation of bacteria in water using suspended titanium dioxide by Javier Marugán; Rafael van Grieken; Cristina Pablos; M. Lucila Satuf; Alberto E. Cassano; Orlando M. Alfano (pp. 404-416).

Display Omitted▶ Succesful mechanistic kinetic modelling of Escherichia coli photocatalytic inactivation. ▶ Reproduction error below 5.3% for a wide range of experimental variables. ▶ A weak bacteria–TiO₂ interaction can be succesfully assumed to simplify the model. ▶ A complex dependence of the reaction rate with the irradiation power is required. ▶ The model can be used in a predictive way for photoreactor design and scaling-up.This study is focused on the kinetic modelling of the photocatalytic inactivation of bacteria with suspended TiO₂. A rigorous model based on a proposed reaction mechanism and accounting explicitly for the rate of photon absorption has been developed. The application of the general kinetic expression to limiting cases suggests that the interaction bacteria–catalyst can be considered to be weak. In contrast, a complex dependence on the radiation absorption rate must be taken into account, as very different radiation conditions may coexist inside the photoreactor, with high absorption rates in the region near to the radiation entrance window and much lower values on the opposite side of the photoreactor. The model has been successfully validated by experimental data, being able to reproduce the evolution of the concentration of viable bacteria in a wide range of values of TiO₂ concentration, irradiation power and initial concentration of bacteria with a normalized root mean square logarithmic error of 5.3%. The values of the kinetic parameters are independent of the specific reactor setup or the operating conditions and therefore, the model can be used in a predictive way for photoreactor design and scaling-up, as well as for the optimization of other reactor configurations.

Keywords: Photocatalysis; Kinetics; Disinfection; Titanium dioxide; Escherichia coli

Synthesis of visible light responsive ZnO–ZnS/C photocatalyst by simple carbothermal reduction by Hongchao Ma; Jihui Han; Yinghuan Fu; Yu Song; Chunling Yu; Xiaoli Dong (pp. 417-423).

Display Omitted▶ Coupled ZnO–ZnS was supported on activated carbon ▶ ZnSO₄ as single precursor ▶ One step synthesis of coupled ZnO–ZnS by heat-treating under open atmospheric conditions. ▶ The activated carbon acted as reducing agent and support in the formation of ZnO–ZnS/C composite catalysts.A new visible light responsive ZnO–ZnS/C photocatalysts have been successfully synthesized by a simple heat-treating procedure using ZnSO₄ as single precursor for the first time. The resultant samples were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and BET surface area measurement. The results showed that the ZnO–ZnS/C catalysts were directly formed by thermal decomposition of ZnSO₄ impregnated on the activated carbon at high temperature under open atmospheric conditions. Here, a possible growth mechanism of the coupled ZnO–ZnS/C photocatalysts was proposed. Activated carbon played both reducing agent and support role in formation of ZnO–ZnS/C catalysts. The photocatalytic activities of catalysts were investigated by degrading reactive brilliant blue K-3R under visible light irradiation. The synthesized catalysts showed excellent photocatalytic activity compared with ZnO/C and pure ZnO, which is ascribed to the formation of ZnO–ZnS heterojunctions in catalysts. Furthermore, influences of preparation conditions on photocatalytic activity of the catalysts have been investigated.

Keywords: Carbothermal reduction; ZnO–ZnS/C; Visible light responsive photocatalyst

Nitrate reduction with hydrogen in the presence of physical mixtures with mono and bimetallic catalysts and ions in solution by Olívia Salomé G.P. Soares; José J.M. Órfão; Manuel Fernando R. Pereira (pp. 424-432).

Display Omitted▶ Activity of physical mixtures of monometallic≥corresponding bimetallic catalysts. ▶ The mixtures with Pd catalysts are the most selective to nitrogen. ▶ Activity of monometallic mixtures is due to in situ formation of bimetallic catalysts. ▶ The noble metal must be supported, copper does not need to be in the metallic form.Several physical mixtures with mono and bimetallic catalysts were tested in the catalytic nitrate reduction with hydrogen. It was observed that the physical mixtures of Pd and Cu or Pt and Cu monometallic catalysts are similar or more active than the corresponding bimetallic catalysts. The mixtures with Pd catalysts are the most selective to nitrogen, being the mixtures with Rh catalysts the most selective to ammonium. The addition of a monometallic catalyst to a bimetallic catalyst does not decrease the accumulation of nitrite in solution neither the formation of ammonium. The activity of the mixture of monometallic catalysts is due to the formation of in situ bimetallic catalysts as a result of the adsorption of the leached copper. The noble metal must be already supported, and copper does not need to be in the metallic form.

Keywords: Nitrate reduction; Monometallic; Bimetallic; Catalysis; Activated carbon

Synthesis of propylene glycol methyl ether from methanol and propylene oxide over alumina-pillared clays by M.N. Timofeeva; V.N. Panchenko; A. Gil; Yu A. Chesalov; T.P. Sorokina; V.A. Likholobov (pp. 433-440).

Display Omitted▶ The aging time of the Al-intercalating solution controls the Al-PILCs properties. ▶ Al-PILCs are very active in synthesis of propylene glycol methyl ether from methanol and propylene oxide. ▶ The aging time of the intercalating solution affects the reaction rate and selectivity for propylene glycol methyl ether.Al-pillared interlayered clays (Al-PILCs) have been synthesized by the exchange reaction between Na-clay and Al-hydroxypolycation solutions aged for 0.5–14 days and characterized by DRS-UV–vis, XRD, FT-IR and N₂-adsorption/desorption analyses, Hammett acidity titration with n-butylamine and FT-IR spectroscopy using PhCN and CDCl₃ as probe molecules. It was found that the aging time of Al-hydroxypolycation pillaring solution affects both the textural characteristics and the physicochemical properties of Al-PILCs. Al-PILCs have been tested as catalysts for synthesis of propylene glycol methyl ether from methanol and propylene oxide. Increase in Al content due to the prolonged aging time favors the increase in the activity of Al-PILCs.

Keywords: Alumina pillared clay; Acid–base properties; Propylene glycol methyl ether; Methanol; Propylene oxide

The ammonia selective catalytic reduction activity of copper-exchanged small-pore zeolites by Dustin W. Fickel; Elizabeth D’Addio; Jochen A. Lauterbach; Raul F. Lobo (pp. 441-448).

Display Omitted▶ Copper-exchanged small-pore zeolites perform much better than Cu-ZSM-5. ▶ An optimal copper loading exists providing both high SCR activity and stability. ▶ Changing the heteroatom in the framework affects the hydrothermal stability. ▶ Cu-SSZ-13 and Cu-SAPO-34 show exceedingly high NH3-SCR activity.The NH₃-SCR activity of the small-pore zeolites, Cu-SSZ-13, Cu-SSZ-16, and Cu-SAPO-34, is investigated using a high-throughput reactor system. These copper exchanged small-pore zeolites have high SCR activity between 150 and 500°C and are shown to be much more hydrothermally stable than the medium-pore zeolite, Cu-ZSM-5. The degree of copper exchange, the dimensionality of the framework, and heteroatom framework substitution all impact the SCR activity and hydrothermal stability of the materials. Of the small-pore zeolites tested, Cu-SSZ-13 and Cu-SAPO-34 display superior SCR performance, both before and after high-temperature hydrothermal treatment.

Keywords: Small-pore zeolites; Selective Catalytic Reduction; NH; ₃; -SCR; Copper Zeolites; SSZ-13; SAPO-34

Destruction of toluene by ozone-enhanced photocatalysis: Performance and mechanism by Haibao Huang; Weibin Li (pp. 449-453).

Display Omitted▶ O₃ was combined with photocatalysis to enhance toluene destruction. ▶ The photocatalytic efficiency and durability was greatly improved with O₃. ▶ The types and amounts of gaseous byproducts were decreased. ▶ The enhancement was attributed to more active species formed. ▶ Both OH and O were responsible for toluene oxidation.The enhanced performance of the ozone-enhanced photocatalysis process (O₃-PCO) on toluene destruction was evaluated and its mechanism was investigated. The toluene removal efficiency (TRE) and stability of O₃-PCO was compared with that of conventional PCO. The gaseous intermediates of toluene oxidation in various processes were analyzed by GC–MS. The formation pathways of main oxidants and their role in toluene destruction were studied. Results indicated that the TRE of O₃-PCO was 8 times higher than that of PCO because more oxidants were generated besides hydroxyl radicals (OH). The generation rate and amount of OH was remarkably increased in the O₃-PCO process which contained more pathways (such as UV/O₃ and O₃/TiO₂) to produce OH besides UV/TiO₂. The GC–MS results showed that the types and amounts of byproducts were dramatically reduced due to the formation of more oxidants and complete oxidation, leading to remarkable enhancement of the photocatalyst's durability in the O₃-PCO process. Its mechanism was greatly different from the conventional PCO. Both OH and active oxygen (O) played a key role in the O₃-PCO process. Based on the intermediates and the main oxidants, possible pathways of toluene degradation were proposed.

Keywords: Ozone-enhanced photocatalysis; Toluene destruction; Mechanism; Intermediate products; Destruction pathway

Heterogeneous photocatalytic degradation of citric acid over TiO₂. I: Mechanism of 3-oxoglutaric acid degradation by Jorge M. Meichtry; Natalia Quici; Gilles Mailhot; Marta I. Litter (pp. 454-463).

Display Omitted▶ UV/TiO₂ 3-oxoglutaric acid degradation is affected by thermal and photocatalytic pathways. ▶ Acetoacetic acid and acetone are produced mainly by thermal degradation. ▶ Formation of lactic, pyruvic, glyoxylic and acetic acid indicates the occurrence of photocatalytic pathways. ▶ Photocatalytic reactions proceed mainly through photo-Kolbe mechanisms.As part of the study on TiO₂-heterogeneous photocatalytic degradation of citric acid (Cit), degradation of 3-oxoglutaric acid (OGA, 5mM, pH 2.8), one of the main intermediates of Cit, was analyzed. As reactive β-ketodicarboxylic acid, OGA decays rapidly in ambient dark conditions to acetoacetic acid and acetone. The photocatalytic reaction over TiO₂ under UV light is thus affected by this thermal pathway and, in addition to the products found in dark conditions, other carboxylic acids like lactic, pyruvic, glyoxylic and acetic acid were detected and quantified. TOC decrease is proven due mostly by the thermal reaction. Kinetic parameters for both thermal and photochemical reactions were obtained from the experimental data, and mechanisms for the TiO₂-photocatalytic degradation were proposed for OGA and its intermediates. The interplay between OGA thermal and photocatalytic decay is verified, a subject not very much described in the literature.

Keywords: Heterogeneous photocatalysis; TiO; ₂; 3-Oxoglutaric acid; Citric acid; Acetoacetic acid

The promoted photoelectrocatalytic degradation of rhodamine B over TiO₂ thin film under the half-wave pulsed direct current by Jing Shang; Yuchao Zhang; Tong Zhu; Qing Wang; Han Song (pp. 464-469).

Display Omitted▶ A PEC technique driven under half-wave pulsed direct current is provided. ▶ The PEC efficiency under half-wave pulsed DC is improved than conventional DC. ▶ The electric induced electron transfer from RhB to TiO₂ is suggested.The photoelectrocatalytic (PEC) degradation of rhodamine B (RhB) over nanosized titanium dioxide (TiO₂) coated working electrode was investigated under the half-wave pulsed direct current (DC). It was found that the PEC degradation of RhB was greatly enhanced under the half-wave pulsed DC mode, compared to under the constant DC mode widely used in the photoelectrochemical cells. It was mostly ascribed to it that the electrons could be more efficiently conducted into the outer circuit under the half-wave pulsed DC, leading to the improved generation of the holes at the surface of TiO₂ working electrode and thereby promoting the PEC oxidation of RhB, relative to under the constant DC. We provide a simple and promising way to improve the photocatalytic oxidation of organic dyes over TiO₂ thin film.

Keywords: Photoelectrocatalysis; Constant DC; Half-wave pulsed DC; TiO; ₂; thin film

Degradation of trichloroethylene using highly adsorptive allophane–TiO₂ nanocomposite by Hiromasa Nishikiori; Masaru Furukawa; Tsuneo Fujii (pp. 470-474).

Display Omitted▶ A highly adsorptive allophane–TiO₂ nanocomposite was prepared by the sol–gel method. ▶ Phosgene emission was drastically inhibited during the trichloroethylene degradation. ▶ Trichloroethylene was transformed into phosgene on the TiO₂ during UV irradiation. ▶ The phosgene was rapidly adsorbed on the allophane. ▶ The phosgene then gradually degraded after diffusing to the TiO₂.A highly adsorptive allophane–TiO₂ nanocomposite photocatalyst was prepared by dispersing nanoparticles of the natural clay mineral allophane into a titanium alkoxide solution by the sol–gel method. During the photocatalytic degradation of trichloroethylene using the allophane–TiO₂ nanocomposite, emission of the intermediate product, phosgene, was drastically inhibited. Trichloroethylene was transformed into the intermediate products, phosgene and dichloroacetyl chloride, on the TiO₂ during the UV irradiation. These compounds are rapidly adsorbed on the allophane. The compounds then gradually degraded after diffusing to the TiO₂.

Keywords: Allophane; Titanium dioxide; Photocatalysis; Trichloroethylene; Adsorption

Efficient low-temperature catalytic combustion of trichloroethylene over flower-like mesoporous Mn-doped CeO₂ microspheres by Hongfeng Li; Guanzhong Lu; Qiguang Dai; Yanqin Wang; Yun Guo; Yanglong Guo (pp. 475-483).

Display Omitted▶ Flower-like mesoporous Mn-doped CeO₂ microspheres were prepared by a hydrothermal method. ▶ Flower-like Ce–Mn–O microspheres have an excellent catalytic activity for TCE combustion. ▶ Flower-like Ce–Mn–O microspheres show much higher catalytic activity than general Ce–Mn–O mixed oxides. ▶ T₅₀ (the temperature for 50% conversion of TCE) over flower-like Ce–Me–O microspheres is as low as 87̊C. ▶ Flower-like mesoporous Ce–Mn–O microspheres have high stability.Flower-like mesoporous Mn-doped CeO₂ microspheres with three-dimensional (3D) hierarchical structures were successfully prepared by a hydrothermal method with the aid of glucose and acrylic acid and subsequent particular thermal treatment, and characterized by SEM, XRD, N₂ adsorption/desorption, H₂-TPR, XPS, Raman spectra and so on. The results show that the atomic ratios of Mn/(Ce+Mn) in the Ce–Mn–O samples as well as their morphologies affect obviously their catalytic performances for low-temperature catalytic combustion of trichloroethylene (TCE). These flower-like Ce–Mn–O microspheres have not only very excellent activity but also high stability, compared with pure flower-like CeO₂ microspheres or bulk Ce–Mn–O samples. The flower-like sample with atomic ratio of Mn/(Ce+Mn) of 0.21 exhibits the best activity, for instance, T₅₀ (the temperature for 50% conversion of TCE) is as low as 87°C, showing much higher catalytic activity than the sample prepared by a co-precipitation or sol–gel method. High surface area, high oxygen mobility and rich surface active oxygen species are responsible for the high catalytic performance of flower-like Mn-doped CeO₂ microspheres, compared with general Ce–Mn–O mixed oxides.

Keywords: Flower-like mesoporous microsphere; Mn-doped CeO; ₂; Hydrothermal synthesis; Trichloroethylene; Catalytic combustion

Determination of kinetics and controlling regimes for H₂ oxidation on Pt/Al₂O₃ monolithic catalyst using high space velocity experiments by Saurabh Y. Joshi; Yongjie Ren; Michael P. Harold; Vemuri Balakotaiah (pp. 484-495).

Display Omitted▶ Method to identify controlling regimes for H₂ oxidation on Pt/Al₂O₃ monolith. ▶ Qualitative difference between fresh and aged catalysts over 30–300°C. ▶ Shift from washcoat/external to external transport control for fresh catalyst. ▶ Shift from washcoat to washcoat/external transport control for aged catalyst. ▶ Analysis suggests pore blockage by sintered Pt leads to diffusion limitations.Recently developed criteria [S.Y. Joshi, M.P. Harold, V. Balakotaiah, Chemical Engineering Science 65 (2010) 1729–1747] are used to characterize the various controlling regimes (kinetic, pore diffusion and mass transfer controlled) during H₂ oxidation on Pt/Al₂O₃ monolithic catalyst. The hydrogen conversion was measured over a wide range of temperatures and space velocities. Experiments at typical space velocities (10⁴–10⁵h⁻¹) revealed that complete conversion can be achieved at ambient temperature, a result of fast catalytic kinetics. The high activity complicates the analysis of the relative importance of reaction, washcoat diffusion and mass transfer. High space velocity operation with accompanying theoretical analysis enabled an efficient determination of the intrinsic catalytic kinetics, quantification of the heat and mass transport coefficients and determination of the resistances due to reaction, washcoat diffusion and external mass transport processes. Specifically, we investigated the effects of catalyst aging, space velocity and catalyst temperature on the regime transition. The analysis reveals that washcoat diffusion regime is dominant over a wide range of temperatures for the aged catalyst whereas the monolith transitions to a mass transfer controlled regime above 90°C for the high dispersion fresh catalyst. The analysis also reveals that the aging of the catalyst due to sintering of Pt crystallites not only reduces the pre-exponential factor but also the observed activation energy.

Keywords: Hydrogen; Platinum; Water; Monolith reactor; Mass transfer controlled regime; Washcoat diffusion; Kinetic regime

Effect of functionalized carbon as Pt electrocatalyst support on the methanol oxidation reaction by J.R.C. Salgado; R.G. Duarte; L.M. Ilharco; A.M. Botelho do Rego; A.M. Ferraria; M.G.S. Ferreira (pp. 496-504).

Display Omitted▶ Spectra showed that after treatments the carbon has been found to have oxygen group. ▶ BET results showed that the functionalized carbon surface was affected. ▶ Uniform dispersion of Pt particles on the surface of carbon was achieved. ▶ Pt catalyst on functionalized carbon presented an improvement of the activity. ▶ Synergistic effect between the metal and oxygenated groups on carbon was found.FTIRS and XPS spectra showed that after oxidative treatments using H₂SO₄+HNO₃ and HNO₃ solutions the Vulcan XC-72R carbon support has been found to be more hydrophilic and richer in oxygen-containing functional groups. Consequently, the Pt electrocatalyst prepared on those functionalized carbon materials further to having good dispersion of metal presented a significant improvement of the electrocatalytic activity due to the synergistic effect between the metal nanoparticles and oxygenated groups on functionalized carbon.

Keywords: Functionalized carbon; Pt electrocatalysts; Methanol oxidation; DMFC

Transesterification of soybean oil on guanidine base-functionalized SBA-15 catalysts by D. Meloni; R. Monaci; Z. Zedde; M.G. Cutrufello; S. Fiorilli; I. Ferino (pp. 505-514).

Display Omitted▶ SBA-15 was successfully functionalized with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD). ▶ All the TBD/SBA-15 catalysts are highly active for soybean oil transesterification. ▶ Catalysts, leaching-resistant in the first run, are deactivated by free fatty acids. ▶ Catalyst regeneration is easily achieved by simple treatment with diluted NaOH. ▶ In subsequent runs samples undergo both deactivation by free fatty acids and leaching.SBA-15 functionalization with the guanidine base 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) was used to prepare TBD-grafted catalysts for the soybean oil transesterification reaction. The structural and textural features of both the support and the catalysts were investigated by X-ray diffraction, transmission electron microscopy, and nitrogen physisorption. CHN analysis and FTIR characterization were also carried out on the catalysts before and after reaction. Potentiometric titration was also used to confirm CHN analysis data for the fresh catalysts. Mild conditions (atmospheric pressure and 343K) were chosen for catalytic testing in a batch reactor. The influence of the base content and the reaction time on the methyl esters yield was investigated. All the catalysts were found active for the soybean oil conversion. Comparison with the catalytic behaviour of a commercial TBD-grafted polymer showed a superior performance of the functionalized SBA-15 catalysts. The higher the functionalization extent, the higher the activity, just a few hours being required for a 100mol% methyl esters yield. Over such a short reaction time leaching was observed to occur only to an extremely low extent, which makes possible to reuse the catalysts after a regeneration step consisting in a simple NaOH treatment of the recovered samples. During such treatment the catalyst base sites – poisoned (through protonation) by the free fatty acids – are freed, and their activity is restored.

Keywords: Soybean oil; Transesterification; TBD-grafted SBA-15; Deactivation; Leaching

Nanoscale β-Sn1−_nWO₄· nα-Sn—A highly efficient photocatalyst for daylight-driven degradation of organic dyes and its real “green” synthesis by Jan Ungelenk; Claus Feldmann (pp. 515-520).

Display Omitted▶ Composite photocatalyst β-Sn1−_nWO₄· nα-Sn consisting of incipient crystalline β-SnWO₄ and α-Sn. ▶ Simple water-based synthesis at ambient temperature. ▶ 20nm sized nanoparticles with high specific surface and electrostatic stabilization. ▶ Photocatalytic activity under simulated daylight 5–10 times higher than TiO₂. ▶ Recycling experiments prove reusability and stability.The unique phase composition β-Sn1−_nWO₄· nα-Sn, including nanoscale incipient crystalline β-SnWO₄ and α-Sn, turned out to be a very promising photocatalyst under simulated daylight. Since the nanomaterial is gained via a quick and simple precipitation in water without using toxic elements or solvents, the synthesis can be regarded as real “green”. Despite its simple preparation, the nanoparticles are of high quality, exhibiting an average diameter of 20nm, a low degree of agglomeration, a high specific surface (71m²g⁻¹) and an efficient electrostatic stabilization ( ζ<−40mV at pH=3.5–9.5). As-prepared β-Sn1−_nWO₄· nα-Sn exhibits a strong absorption in the visible spectral range (554nm, 2.2eV) and a lasting high photocatalytic performance under simulated daylight. Various organic dyes (phenothiazine dye methylene blue, triphenylmethane dye basic green 4, azo-dye methyl red) are decomposed with significantly higher degradation rates (5–10) as compared to commercially available Degussa P25 (TiO₂, 80% anatase, 20% rutile). Recycling experiments prove the phase stability and reusability of as-prepared β-Sn1−_nWO₄· nα-Sn.

Keywords: Tin tungstate; Tin; Nanoparticle; Photocatalysis; Daylight-driven; Green synthesis

A model study on the carburization process of iron-based Fischer–Tropsch catalysts using in situ TEM–EELS by S. Janbroers; P.A. Crozier; H.W. Zandbergen; P.J. Kooyman (pp. 521-527).

Display Omitted▶ During carburization inside an ETEM at 20Torr CO, hematite precursors are reduced. ▶ During, or shortly after the reduction of hematite, severe sintering occurs. ▶ The reduction inside the ETEM is so effective that metallic iron can be formed. ▶ No carbon deposits were found on the outer rim of the iron carbides.In order to elucidate the activation mechanism of iron based Fischer–Tropsch catalysts, we performed in situ nanoscale structural and compositional analysis during carburization in CO atmosphere. We found that inside an ETEM at 20Torr CO, hematite reduces while severe sintering occurs. This sintering is enhanced by low pressure conditions in combination with CO gas. The reduction inside the ETEM is so effective that metallic iron can be formed. During the process, about 50nm sized iron carbide crystallites grow out of the iron (oxide) particles. Upon prolonged reaction, these newly formed crystallites reduce in size to about 5–30nm. In contrast to what has been described in the literature until now, no carbon deposits were found on the outer rim of these iron carbides at high temperature conditions. Note however that, in contrast to our measurements, previous studies involved catalysts that were cooled or passivated prior to (TEM) analysis.

Keywords: Fischer–Tropsch; Carburization; TEM–EELS

Steam reforming of tar from pyrolysis of biomass over Ni/Mg/Al catalysts prepared from hydrotalcite-like precursors by Dalin Li; Lei Wang; Mitsuru Koike; Yoshinao Nakagawa; Keiichi Tomishige (pp. 528-538).

Display Omitted▶ Calcination–reduction of the hydrotalcite precursors gives Ni/Mg/Al catalysts. ▶ The optimized Ni/Mg/Al showed high activity and stability in tar steam reforming. ▶ The Ni/Mg/Al catalyst has a nanocomposite consisted of Ni particles and Mg(Ni, Al)O. ▶ The aggregation of Ni particles and coke deposition were suppressed on this catalyst.The Ni/Mg/Al catalysts were prepared from the calcination and reduction of hydrotalcite-like compounds containing Ni, Mg and Al, and applied to the steam reforming of tar from pyrolysis of biomass. The dependence of the composition and reduction pretreatment conditions on the catalytic performance was investigated. It is found that the Ni/Mg/Al catalyst with optimized composition of Ni/Mg/Al=9/66/25 exhibited much higher activity, resistance to coke deposition, and stability than Al₂O₃- and MgO-supported Ni catalysts. The catalyst characterization using XRD, TPR, N₂ and H₂ adsorption, and TEM indicates that the Ni/Mg/Al catalyst after the reduction has a nanocomposite structure of Ni metal particles (about 8.5nm) and Mg(Ni, Al)O particles (about 11.5nm). Even after the catalytic use, the nanocomposite structure was maintained. High performance of the Ni/Mg/Al catalyst including the suppression of the aggregation of the metal particles can be caused by the nanocomposite structure.

Keywords: Steam reforming; Tar; Biomass; Synthesis gas; Hydrotalcite

Catalytic ozonation of organic pollutants in the presence of cerium oxide–carbon composites by C.A. Orge; J.J.M. Órfão; M.F.R. Pereira (pp. 539-546).

Activated carbon–ceria composite as ozonation catalysts.Display Omitted▶ A synergic effect occurs when ceria–carbon composites are used as ozonation catalysts. ▶ Catalytic activity increases with the amount of carbon present in the composites. ▶ Total degradation of oxalic acid was obtained in less than 90min for all catalysts. ▶ Surface reactions are predominant over liquid bulk reactions involving HO radicals.Cerium oxide–carbon composites were prepared and tested as ozonation catalysts for the removal of two selected carboxylic acids, oxalic and oxamic, and one textile dye (C.I. Reactive Blue 5). The results were compared with those obtained in non-catalytic ozonation and ozonation catalysed by cerium oxide and carbon materials (activated carbon, carbon xerogel). With the exception of cerium oxide, a total degradation of oxalic acid was obtained in approximately 90min for all prepared catalysts and the catalytic activity increases with the amount of carbon present in the composites. Despite of oxamic acid be more refractory to ozonation than oxalic acid, 75% of oxamic acid removal was achieved after 10h of reaction in the presence of the ceria-activated carbon composite with 90% of carbon material. In the mineralization of the textile dye, the catalytic activity of the composites increases with the amount of activated carbon introduced.

Keywords: Catalytic ozonation; Cerium oxide; Carbon materials; Carboxylic acids; Textile dye

Influence of the reducing agent for lean NO_x reduction over Cu-ZSM-5 by Sara Erkfeldt; Anders Palmqvist; Martin Petersson (pp. 547-554).

.Display Omitted▶ The molecular structure of reducing agents determines their NO_x reduction capacity. ▶ Zeolite Cu-ZSM-5 requires a C–C bond in the reducing agent for lean NO_x reduction. ▶ DME and methanol do not reduce NO_x over Cu-ZSM-5, but ethylene glycol does.A range of ethers, alcohols and alkanes were compared as reducing agents for NO_x over a Cu-ZSM-5 lean NO_x catalyst. The nature of the reducing agent was found to determine the degree of NO_x reduction. Methanol and DME were virtually inactive as reductants over this catalyst, while higher ethers and alcohols showed high NO_x conversion. A detailed study was performed to investigate the differences. Among the studied variables, the chemical structure of the reductant was found to be especially important. Despite having a lower reducing capacity than DME, ethylene glycol was active for NO_x reduction. It is concluded that a C–C bond in the reducing agent is required for lean NO_x reduction over Cu-ZSM-5. The absence of this bond in DME and methanol explains their low activity for NO_x reduction over this catalyst.

Keywords: Hydrocarbon-SCR; NO; _x; reduction; Zeolite; Alternative fuel; Dimethyl ether; Alcohol; Ether; Alkane; Reducing agent; Cu-ZSM-5

Heterogeneous photocatalytic degradation of citric acid over TiO₂ by Jorge M. Meichtry; Natalia Quici; Gilles Mailhot; Marta I. Litter (pp. 555-562).

.Display Omitted▶ By UV/TiO₂ citric acid is degraded almost quantitatively to 3-oxoglutaric acid. ▶ Acetoacetic, lactic, pyruvic, malic, glyoxylic, acetic and formic acids plus acetone are intermediate products. ▶ While citric acid is present the intermediates are not photocatalytically degraded. ▶ Simple kinetic equations can explain the citric acid photocatalytic degradation. ▶ Using a different irradiation setup, similar kinetic parameters are obtained.The degradation pathways for citric acid (Cit, 5mM, pH 2.8) degradation by TiO₂-heterogeneous photocatalysis were studied through the analysis of its degradation intermediate products. The most important product formed was 3-oxoglutaric acid, but several other compounds, like acetoacetic, lactic, pyruvic, malic, glyoxylic, acetic and formic acids plus acetone were found. While citric acid is present, the intermediates cannot be photocatalytically degraded.The importance of the geometry of the photoreactor and the photon flux on the formation of 3-oxoglutaric acid from citric acid was studied in a different irradiation setup (at [Cit]=2mM, pH 2.0), where reaction rates were one order of magnitude higher. With these results and those obtained in part I of this work, mechanisms for TiO₂-photocatalytic degradation of citric acid were proposed, and related with the OGA photocatalytic and thermal decays already studied.

Keywords: Heterogeneous photocatalysis; TiO; ₂; Citric acid; 3-Oxoglutaric acid

Kinetics and mechanism of aqueous degradation of carbamazepine by heterogeneous photocatalysis using nanocrystalline TiO₂, ZnO and multi-walled carbon nanotubes–anatase composites by C. Martínez; M. Canle L.; M.I. Fernández; J.A. Santaballa; J. Faria (pp. 563-571).

.Display Omitted▶ A detailed mechanism is proposed for the photocatalytic degradation of carbamazepine. ▶ The efficacy of composites MWCNT-TiO₂ is discussed and compared with TiO₂. ▶ The mechanism of action of MWCNT-TiO₂ composites is analyzed. ▶ The effects of the variables affecting the process are discussed.The photocatalytic degradation of Carbamazepine (CBZ), 5 H-dibenzo[b,f]azepine-5-carboxamide, under near UV–Vis and UV irradiation is studied using P25, synthesized TiO₂ (anatase and rutile), mechanical mixtures and composites of oxidized-multi-walled-carbon-nanotube:anatase, and ZnO suspensions as catalyst, to identify intermediates, and to elucidate its degradation mechanism. Factors affecting the kinetics of the process, such as the type and load of photocatalyst, and the presence of dissolved O₂ or addition of co-oxidants (H₂O₂), have been compared. Optimal conditions for degradation were obtained using P25 (0.5g/L), 5mM of H₂O₂ or 50% O₂ (v/v), with rate constants ca. 0.3144min⁻¹ and 0.2005min⁻¹, respectively. Complete removal of CBZ was achieved, showing the efficiency of the photocatalytic process. Ten photoproducts of CBZ were assigned by using high-resolution mass spectrometry, the most important of which identified as 10,11-dihydro-CBZ-10,11-epoxide, in accordance with the literature. The reaction mechanism includes previous proposals, and accounts for the pathways giving rise to the identified photoproducts.

Keywords: Persistent organic pollutants; Heterogeneous photocatalysis; Carbon nanotubes; Carbamazepine; Reaction mechanism

Photocatalytic degradation of organics in water in the presence of iron oxides: Effects of pH and light source by Eva M. Rodríguez; Guadalupe Fernández; Pedro M. Álvarez; Rebeca Hernández; Fernando J. Beltrán (pp. 572-583).

Display Omitted▶ The efficiency of the oxidizing systems (combinations of UV-A/iron oxides/oxalic acid/TiO₂/H₂O₂) studied in the black light photoreactor have been classified. ▶ In the presence of solar radiation, BPA degradation rate increased due to the higher UV-A energy supplied in the CPC photoreactor. ▶ The performance of systems that do not require iron dissolution, directly depends on the accumulated UV-A energy in the photoreactor regardless of the source of radiation. ▶ For those systems requiring iron dissolution, the performance depends not only on the accumulated UV-A energy but also on the liquid-solid contact time. ▶ For the different systems tested, visible solar radiation does not seem to contribute to BPA degradation which is mainly due to UV radiation of wavelength lower than 400nm.The effects of pH on the performance of different photocatalytic oxidizing systems involving iron oxides, oxalic acid, hydrogen peroxide and titanium dioxide for the removal of bisphenol A (BPA) and its degradation phenolic intermediates, have been studied. For that purpose two photoreactors have been used: one irradiated with black light lamps and the other with solar radiation.Effects related to iron dissolution, generation/photoreduction of ferrioxalate and accumulated UV-A energy in the photoreactors are discussed in terms of BPA and total polyphenol (TP) degradations, TOC elimination (i.e., mineralization), accumulation of iron in solution and hydrogen peroxide disappearance rate. Solar radiation was found to be more efficient than the black light lamps used due to the higher flux of UV-A radiation supplied. When results were expressed as a function of the accumulated UV-A energy, however, no significant differences were observed on organic degradation rates when using one or another radiation source with the exception of the systems where hydroxyl radical formation goes through, at least in some extent, iron oxides dissolution in the presence of oxalic acid. For these cases, in addition to the accumulated UV-A energy, contact time between oxalic acid and iron oxides played a key role in the process.

Keywords: Bisphenol A; Photocatalytic oxidation; Iron oxides; Hematite; Magnetite; Carboxylic acids; Titanium dioxide; Hydrogen peroxide

d-Glucose oxidation with H₂O₂ on an Au/Al₂O₃ catalyst by Ramona Saliger; Nadine Decker; Ulf Prüße (pp. 584-589).

Display Omitted▶ Oxidation ofd-glucose to sodiumd-gluconate with H₂O₂ on a 0.3% Au/Al₂O₃ catalyst. ▶ Selectivity exceeded 99%. ▶ High catalyst activity of about 8300mmolmin⁻¹g_Au⁻¹ at mild reaction conditions and atmospheric pressure. ▶ Effective oxidizing agent is formed by the decomposition of H₂O₂ on the gold catalyst. ▶ High catalyst activity and selectivity was obtained in oxidation ofd-maltose.The oxidation ofd-glucose to sodiumd-gluconate with H₂O₂ has been investigated using an industrially relevant 0.3% Au/Al₂O₃ catalyst. The selectivity surprisingly exceeded 99% atd-glucose conversions >99%. Furthermore, high catalyst activity of about 8300mmolmin⁻¹g_Au⁻¹ was obtained at mild reaction conditions (40°C, pH 9) and atmospheric pressure. The concentration of dissolved oxygen was tracked for most experiments and showed that the effective oxidizing agent is formed by the decomposition of H₂O₂ on the gold catalyst. Investigations on the reaction kinetics showed an apparent activation energy of 48kJmol⁻¹ and a reaction order ford-glucose of 0.5, which both correspond to the values reported ford-glucose oxidation with O₂. In addition, the oxidation ofd-maltose, as a model disaccharide, to sodiumd-maltobionate with H₂O₂ was studied. The results show that H₂O₂ is a very interesting alternative oxidizing agent for the selective oxidation ofd-maltose as well.

Keywords: Gold; Glucose oxidation; Hydrogen peroxide; Maltose oxidation; Selective oxidation

Consequences of the iron–aluminium exchange on the performance of hydrotalcite-derived mixed oxides for ethanol condensation by Marta León; Eva Díaz; Aurelio Vega; Salvador Ordóñez; Aline Auroux (pp. 590-599).

Display Omitted▶ The substitution of Al by Fe in the MgAl hydrotalcite-derived mixed oxides only leads slight variations in crystallographic and morphological properties. ▶ This substitution leads to sharp decreases in the surface acidity of the materials, whereas the surface basicity slightly decreases. ▶ MgFe mixed oxide present higher selectivities for C4 fraction (especially 1,-butanol), largely decreasing the selectivity for ethylene and C4 olefins. ▶ Fe is present in the oxides as Fe³⁺, but its redox properties do not play any significant role in the reaction pathways.The effect of the partial and total substitution of aluminium by iron on the performance of different hydrotalcite-derived mixed oxides for the condensation of ethanol for obtaining valuable C4 products (mainly butanol and 1,3,-butadiene) has been studied in this work. Ethanol condensation reactions have been performed in a fixed bed reactor at 0.1MPa, WHSV=0.215h⁻¹ and 473–723K. Three different hydrotalcite-derived mixed oxide with an atomic Mg²⁺/M³⁺ ratio of 3 (namely Mg₆Al₂O₉, Mg₆AlFeO₉ and Mg₆Fe₂O₉) have been prepared by a previously optimized procedure, tested as catalyst for the above mentioned reaction and characterized by TG–DTG, NH₃-TPD, CO₂ adsorption (calorimetric, TG–DTG and FTIR), Mossbauer Spectroscopy and TPR.The substitution of Al³⁺ by Fe³⁺ in the structure of the resulting mixed oxide leads to a slight decrease of the basic sites and a more marked decrease of the concentration of acid sites, being the concentration of these last sites negligible when the Al³⁺ cation is completely replaced by Fe³⁺. Accordingly, Mg–Fe mixed oxide is the most selective catalyst for the formation of C4 compounds, especially butanol. The almost total abatement of the acid sites of this material largely decrease the selectivity for ethanol dehydration, resulting in an increase of the formation of the dehydrogenation product (acetaldehyde), key reactant for condensation reactions.

Keywords: Bioethanol upgrading; Base catalysis; Aldol condensation; Guerbet reaction; C4 alcohols; Mössbauer Spectroscopy

Comparative photoactivity of CeO₂, γ-Fe₂O₃, TiO₂ and ZnO in various aqueous systems by Samuel W. Bennett; Arturo A. Keller (pp. 600-607).

Display Omitted▶ Oscillator strength is a suitable a priori tool to assess the photoactivity of metals oxides ▶ A UV-transparent microplate is a rapid, reliable and suitable reaction vessel. ▶ At environmentally relevant concentrations, photoactive metal oxide nanomaterials have limited reactivity.Photoactive nanomaterials may be released into natural water systems where the interactions with ambient light and natural water chemistry are largely unknown. Using a high-throughput approach, the photoactivity of four nanoscale metal oxides was investigated, at various environmentally relevant concentrations. Photoactivity was measured in deionized water at various pH and also in seawater. TiO₂ was the most photoactive nanoparticle under most deionized conditions followed by γ-Fe₂O₃, ZnO and CeO_2. In natural seawater ZnO replaced TiO₂ as the most photoactive nanomaterial and was followed in decreasing photoactivity by TiO₂. In seawater, CeO₂ reduced the degradation of the organic probe, suggesting the ability of CeO₂ to act as an antioxidant. The high-throughput method developed in this research enables a rapid, reproducible and accurate assessment of nanomaterial photoactivity.

Keywords: Nanomaterials; Photocatalysis; Photoactivity; Natural waters; TiO; ₂

Preparation of Pt_shell–Pd_core nanoparticle with electroless deposition of copper for polymer electrolyte membrane fuel cell by Insoo Choi; Sang Hyun Ahn; Jae Jeong Kim; Oh Joong Kwon (pp. 608-613).

.Display Omitted▶ Pt layer is formed on Pd via two successive processes; electroless deposition of Cu and its displacement with Pt. ▶ Pt_shell–Pd_core exhibits higher catalytic activity than conventional Pt catalyst. ▶ Pt_shell–Pd_core contains small amount of Pt leading to high mass-specific activity.High over-potential induced by the irreversibility of oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cell (PEMFC) causes low cell performance. In order to overcome such a problem, many research groups have been studying to enhance the catalytic activity of platinum in fuel cell. In this regard, Pt_shell–Pd_core (Pt/Pd/C) nanoparticle was prepared by electrochemical method in this study. The home-made Pd/C was surrounded by Cu as a result of electroless deposition (ELD) which was followed by displacement reaction with Pt. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were applied to identify metallic composition. Transmission electron microscope (TEM) was adopted to image the catalysts. Besides, the catalytic properties were investigated using rotating disk electrode (RDE). The results indicated that the kinetics of electrochemically-prepared Pt/Pd/C catalyst for O₂ reduction was superior to conventional Pt/C catalyst and the feasibility of electroless deposition in fabricating electro-catalyst was confirmed through the formation of Cu ad-layer.

Keywords: Oxygen reduction reaction; Electroless deposition of Cu; Pt; _shell; –Pd; _core; catalyst; Polymer electrolyte membrane fuel cell

Preparation of Pd–Au/C catalysts with different alloying degree and their electrocatalytic performance for formic acid oxidation by Guojie Zhang; Yanen Wang; Xin Wang; Yu Chen; Yiming Zhou; Yawen Tang; Lude Lu; Jianchun Bao; Tianhong Lu (pp. 614-619).

Display Omitted▶ THF can obviously enhance the alloying degree of Pd–Au nanoparticles during the preparation of Pd–Au/C catalyst. ▶ The addition of Au could decrease the adsorption strength of CO on Pd, and promote the electrocatalytic oxidation of formic acid, especially when the alloyed Au is introduced. ▶ The electrocatalytic activity of Pd–Au/C catalyst for the formic acid electrooxidation is strongly dependent on alloying degree of Pd–Au nanoparticles. The Pd–Au/C catalyst with high alloying degree shows a higher electrocatalytic activity and stability for the formic acid electrooxidation.The carbon-supported Pd–Au catalysts (Pd–Au/C) with different alloying degree are prepared in the aqueous solution with and without tetrahydrofuran (THF) by a chemical reduction method. The studies of X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) measurements show that the alloying degree of the Pd–Au/C catalyst prepared in the aqueous solution is much lower than that of Pd–Au/C catalyst prepared in the H₂O/tetrahydrofuran (THF) mixture solution, indicating the presence of THF can obviously enhance the alloying degree of Pd–Au nanoparticles during the preparation of Pd–Au/C catalyst. The electrochemical measurements illustrate the electrocatalytic activity of Pd–Au/C catalyst for the formic acid electrooxidation is strongly dependent on alloying degree of Pd–Au nanoparticles. The Pd–Au/C catalyst with high alloying degree shows a higher electrocatalytic activity and stability for the formic acid electrooxidation compared to the Pd–Au/C catalyst with low alloying degree, which can be ascribed to enhancement of CO tolerance and possible suppression of dehydration pathway in the course of formic acid electrooxidation.

Keywords: Pd–Au/C catalyst; Alloy; Formic acid; Oxidation; Electrocatalytic performance

Improvement in sulfur desorption of NO_X storage and reduction catalysts using a Ba–Ti composite oxide by Toshiyuki Tanaka; Ichirou Tajima; Yuichi Kato; Yasushi Nishihara; Hirofumi Shinjoh (pp. 620-626).

Display Omitted▶ Highly dispersed Ba–Ti composite oxide was formed using an improved complex method. ▶ The Ba–Ti composite oxide enhanced sulfur desorption efficiency. ▶ The utilization of Ba–Ti composite improved the durability of NSR catalysts.A Ba–Ti composite oxide was formed on a NO x storage and reduction catalyst via impregnation of a Ba–Ti precursor solution composed of H₂O₂ added to a complex prepared using the citric acid method. The structure of the Ba–Ti composite in solution was analyzed by chemical composition analysis and FT-Raman and UV–vis spectroscopy. MM2 calculations were performed to propose its chemical structure. Both Ba and Ti together were found to form a composite molecule in the solution. Furthermore, TEM-EDX and XRD analyses of the Ba–Ti composite oxide on the catalyst prepared by impregnation with the Ba–Ti composite aqueous solution revealed that Ba and Ti in the catalyst were highly dispersed at the nm scale. The formation of the Ba–Ti composite oxide on the NSR catalyst enhanced sulfur desorption efficiency and led to high-performance NO_X conversion as a NO_X storage and reduction activity catalyst after desulfation treatment. It was assumed that the existence of nano-scaled Ba compounds combined with Ti was efficient for the inhibition of the sintering of barium sulfate and its facile decomposition. It was found that dispersion of Ba compounds for NO_X storage materials using a Ba–Ti complex solution is an efficient way to improve the durability of NSR catalysts.

Keywords: NSR catalyst; Desulfation; Barium sulfate; Titanium oxide; Citric acid

Effect of thermal treatments on the catalytic behaviour in the CO preferential oxidation of a CuO–CeO₂–ZrO₂ catalyst with a flower-like morphology by Elisa Moretti; Loretta Storaro; Aldo Talon; Maurizio Lenarda; Piero Riello; Romana Frattini; María del Valle Martínez de Yuso; Antonio Jiménez-López; Enrique Rodríguez-Castellón; Fátima Ternero; Alfonso Caballero; Juan P. Holgado (pp. 627-637).

Display Omitted▶ A nanostructured Ce/Zr/Cu oxide system with a flower-like morphology was prepared. ▶ The effect of four different thermal treatments on the active species was evaluated. ▶ The CO-PROX catalytic activity was correlated with the structural characteristics.A Ce–Zr–Cu oxide system with a flower-like morphology was prepared by a slow co-precipitation method in the absence of any structure directing agent. Four portions of the oxide were thermally treated at four different temperatures (350°C, 450°C, 550°C, 650°C). The resulting materials samples were characterized by quantitative XRD, adsorption–desorption of N₂ at-196°C, SEM and TEM microscopy, –H₂-TPR, XPS and Operando-XANES. All samples were tested in the preferential CO oxidation (CO-PROX) in the 40–190°C temperature range. Thermal treatments were found to induce slight structural changes without altering the starting morphology of the samples. The samples treated at higher temperature 550–650°C showed a quite interesting CO-PROX activity and selectivity in a temperature range suitable for a practical use within the FEMFC technology.

Keywords: Hydrogen; CO-PROX; Copper; Ceria–zirconia; Flower-like morphology

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Applied Catalysis B, Environmental (v.102, #3-4)

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Applied Catalysis B, Environmental (v.102, #3-4)