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Applied Catalysis B, Environmental (v.102, #1-2)

Contents Continued (pp. i).

Editorial Board (pp. i).

Editorial Board (pp. co2).

Contents (pp. co4).

Carbon nanotube-supported metal catalysts for NO_x reduction using hydrocarbon reductants. Part 1: Catalyst preparation, characterization and NO_x reduction characteristics by Eduardo Santillan-Jimenez; Vladimir Miljković-Kocić; Mark Crocker; Karen Wilson (pp. 1-8).

Display Omitted▶ A dual catalytic system is proposed for the reduction of NO_x in diesel exhaust. ▶ This system would include distinct low and high temperature formulations. ▶ Supporting Pt on carbon nanotubes affords active low temperature HC-SCR catalysts. ▶ Acid treating the nanotubes results in further improvements in deNO_x performance. ▶ A 3:1 Pt–Rh alloy is the most promising active phase found in this work.A dual catalyst system for the Selective Catalytic Reduction of NO_x with hydrocarbons (HC-SCR), including distinct low and high temperature formulations, is proposed as a means to abate NO_x emissions from diesel engines. Given that satisfactory high temperature HC-SCR catalysts are already available, this work focuses on the development of an improved low temperature formulation. Pt supported on multiwalled carbon nantubes (MWCNTs) was found to exhibit superior NO_x reduction activity in comparison with Pt/Al₂O₃, while the MWCNT support displayed a higher resistance to oxidation than activated carbon. Refluxing the MWCNT support in a 1:1 mixture of H₂SO₄ and HNO₃ prior to the metal deposition step proved to be beneficial for the metal dispersion and the NO_x reduction performance of the resulting catalysts. This support effect is ascribed to the increased Brønsted acidity of the acid-treated MWCNTs, which in turn enhances the partial oxidation of the hydrocarbon reductant. Further improvements in the HC-SCR performance of MWCNT-based formulations were achieved using a 3:1 Pt–Rh alloy as the supported phase.

Keywords: NO; _x; -Selective Catalytic Reduction; Hydrocarbons; Carbon nanotubes; Pt; Rh; Alloys

Methanol oxidation on Pt/CeO₂–C electrocatalyst prepared by microwave-assisted ethylene glycol process by Da-Ming Gu; Yuan-Yuan Chu; Zhen-Bo Wang; Zheng-Zhi Jiang; Ge-Ping Yin; Yang Liu (pp. 9-18).

.Display Omitted▶ The interaction of carbon black and CeO₂ enhances the stability of mixed support. ▶ CeO₂ evidently improves the dispersion of Pt nanoparticles on mixture support. ▶ The activity enhancement of Pt/CeO₂–C comes from the interaction of Pt and CeO₂. ▶ The stability improvement of Pt/CeO₂–C catalyst results from the anchor of CeO₂.Pt/C and Pt/CeO₂–C catalysts with different CeO₂ contents were prepared by microwave-assisted polyol process and characterized by energy dispersive analysis of X-ray (EDAX), X-ray diffraction (XRD), elemental mapping by X-ray energy dispersive spectroscopy (XEDS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) in this study. Their electrochemical activities and stabilities for methanol electrooxidation were evaluated by cyclic voltammetry, amperometric i– t, electrochemical impedance spectroscopy (EIS), and continued cyclic voltammograms cycles. The results show that the stability of the mixture support with Vulcan XC-72 carbon black and homemade CeO₂ nanomaterial is evidently enhanced in comparison with that of single carbon black, which results from anti-corrosion property of CeO₂ and the interaction between CeO₂ and XC-72 carbon black. And the appropriate content CeO₂ may significantly improve the dispersion of Pt nanoparticles on surface of the mixture support. Too much content CeO₂ may lead to the agglomeration of Pt nanoparticles. The optimal weight ratio of CeO₂ is 20wt.% in Pt/CeO₂–C catalyst with narrower particle size distribution and better dispersion on surface of the mixture support, which exhibits the best activity and stability for methanol electrooxidation among all the samples. The reason for the increased activity and stability is ascribed to the promotion of CO_ads electrooxidation reaction kinetics by CeO₂, the stability of the CeO₂–C mixture support in acidic media, as well as the improvement of CeO₂ for the dispersion of Pt nanoparticles. The addition of CeO₂ into carbon black as a mixture support also can improve the hydrophilicity and wettability of carbon, and this particularity was fully made use of to achieve the Pt deposition on the contact interface of CeO₂ and carbon black smoothly, avoiding the addition of other polymer conductive electrolyte or surfactant.

Keywords: Direct methanol fuel cell; Pt/CeO; ₂; –C catalyst; Microwave-assisted polyol process; Methanol electrooxidation

An easily recyclable Co/SBA-15 catalyst: Heterogeneous activation of peroxymonosulfate for the degradation of phenol in water by Longxing Hu; Xiaping Yang; Songtao Dang (pp. 19-26).

Display Omitted▶ The 10wt%Co/SBA-15 calcined at 400°C for 5h has the best performance. ▶ The formation of Co–O–Si species during the calcination inhibits Co leaching. ▶ High PMS dosage and low initial phenol concentration improve the degradation effect. ▶ The Co/SBA-15 powder wrapped with PTFE membranes exhibits excellent operational stability. ▶ High TOC reduction nearly 100% is achieved.A powder Co/SBA-15 catalyst for the activation of peroxymonosulfate (PMS) and the subsequent degradation of phenol was prepared through an incipient wetness impregnation technique using SBA-15 as the support, Co(NO₃)₂·6H₂O as the precursor. A facile way to make a recyclable Co/SBA-15 catalyst was tested. The samples synthesized were characterized by X-ray diffraction (XRD), N₂ adsorption–desorption, high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) techniques. Effects of Co loading, calcination temperature and time on the performance of the powder catalyst were investigated. The results show that Co₃O₄ was the main cobalt species present both inside and outside the support. Heat treatment led to the formation of Co–O–Si species during the calcinations and significantly inhibited Co leaching. The 10wt%Co/SBA-15 calcined at 400°C for 5h had the best performance, with the phenol removal of more than 98% and total organic carbon (TOC) reduction of approximately 98%. The complete mineralization of phenol degradation was demonstrated, and the degradation mechanism was analyzed. Moreover, effects of PMS dosages and phenol concentrations on phenol degradation were also investigated. The results show that the appropriately high PMS dosage and the low phenol concentration were favorable to phenol removal. During 25 runs of recycling tests, the powder Co/SBA-15 wrapped with polytetrafluoroethylene (PTFE) membranes always maintained high catalytic activity with the phenol removal more than 90% in 2h and Co leaching of less than 85μg/L. Consequently, it is an easily recyclable catalyst.

Keywords: Co/SBA-15 catalyst; Peroxymonosulfate; Phenol degradation; Recycle; Hydrophilic polytetrafluoroethylene membrane

Preparation and desulfurization performance of LaMeO_x/SBA-15 for hot coal gas by B.S. Liu; X.N. Wei; Y.P. Zhan; R.Z. Chang; Fazle Subhan; C.T. Au (pp. 27-36).

Display Omitted▶ Metal oxides supported on SBA-15 effectively suppress mechanical disintegration. ▶ LaFeO₃/SBA-15 presented high BET surface area and big channel structure. ▶ Mesoporous desulfurizer promoted the diffusion of H₂S during desulfurization.LaMeO_x/SBA-15 (Me=Zn, Co and Fe) desulfurizers were synthesized by a sol–gel method and their performance for H₂S removal from hot coal gas was investigated. The results of eight successive desulfidation–regeneration cycles revealed that the LaFeO₃/SBA-15 desulfurizer shows high performance and stability for H₂S removal. The results of BET, XPS, HRTEM and XRD characterization suggested that the SBA-15 structure of used LaMeO_x/SBA-15 remained intact. It was found that there is only partial reduction of Fe³⁺ ions in LaFeO₃/SBA-15 by hydrogen in hot coal gas, a factor considered to be favorable for LaFeO₃/SBA-15 sulfidation. The metal oxides supported on SBA-15 can effectively suppress mechanical disintegration and improve stability of LaMeO_x/SBA-15. Among the three desulfurizers, LaFeO₃/SBA-15 performs the best.

Keywords: Desulfurizers; Hot coal gas; SBA-15; Rare earth metal oxides

Catalyzed oxidative degradation of methylene blue by in situ generated cobalt (II)-bicarbonate complexes with hydrogen peroxide by Aihua Xu; Xiaoxia Li; Shuang Ye; Guochuan Yin; Qingfu Zeng (pp. 37-43).

Display Omitted▶ Efficient degradation of methylene blue was disclosed with Co²⁺–HCO₃⁻/H₂O₂ system. ▶ The system produces hydroxyl radicals as the main reactive species. ▶ Different complex species in situ formed between Co²⁺ and HCO₃⁻ were observed at different HCO₃⁻ concentrations. ▶ The complex [Co(HCO₃)]⁺ formed at intermediate HCO₃⁻ concentrations (5–10mM) was suggested more active than the others.Oxidative degradation of methylene blue (MB) by Co²⁺–HCO₃⁻ system with H₂O₂ in aqueous solution was studied. Nearly complete decolorization of the dye was obtained in less than 50min in diluted NaHCO₃ solution (25mM) in the presence of only 20μM Co²⁺ ions. Meanwhile, the conjugated structure and phenyl rings of the MB molecule were destroyed or even broken down into small organic acids and inorganic ions, as indicated by FT-IR spectra and ion-chromatography. Photoluminescence probing and radical scavenging technologies suggested that the reaction of MB degradation in this system mainly involved the generation and participation of hydroxyl radicals. Furthermore, by cyclovoltammetric measurements, the in situ formed different complexes between Co²⁺ and HCO₃⁻ were observed at different HCO₃⁻ concentrations, and the complex [Co(HCO₃)]⁺ formed at intermediate HCO₃⁻ concentrations (5–10mM) was suggested to be more active than the others.

Keywords: Cobalt; Bicarbonate; Hydrogen peroxide; Degradation; Methylene blue; Hydroxyl radicals

Thermodynamic and experimental studies of catalytic reforming of exhaust gas recirculation in gasoline engines by S. Rijo Gomes; N. Bion; G. Blanchard; S. Rousseau; V. Bellière-Baca; V. Harlé; D. Duprez; F. Epron (pp. 44-53).

Display Omitted▶ REGR process prevents misfires and partial burns that can be caused by excessive EGR in a spark-ignited engine. ▶ Rh (1wt%) supported over zirconia modified with appropriate amount and nature of dopants offers very high activity and good stability in REGR conditions. ▶ High H₂ yield is obtained due to limitation in CH₄ formation.The catalyst 1wt% Rh supported on ZrO₂(73.8wt%)–La₂O₃–Nd₂O₃–Y₂O₃(26.2wt%) was tested for the reforming of exhaust gas recirculation (REGR) on gasoline engines. Isooctane (C₈H₁₈) was used as molecule representative of gasoline, and N₂, H₂O, CO₂ and O₂ were used as model exhaust gas. Despite the moderate C₈H₁₈ conversion (58–70%) and a slight initial deactivation, good stability and activity were obtained even after hydrothermal treatment of the catalyst, leading to a gas phase composition close to thermodynamic equilibrium. The volume proportion of H₂ produced in the gas phase achieved 14% which is consistent with the sake of the application.The high hydrogen yield was linked to the very low methane production. C₈H₁₈ steam reforming (SR) and C₈H₁₈ dry reforming (DR) reactions in REGR conditions were also studied. The presence of CO₂ decreased the H₂ yield expected with respect to SR reaction. A suitable model based on experimental isooctane conversion and thermodynamic calculations predicted this result.

Keywords: EGR; Steam reforming; Dry reforming; Hydrogen production; Isooctane; Thermodynamic model

Catalytic removal of nitrates from waters in a continuous flow process: The remarkable effect of liquid flow rate and gas feed composition by Christodoulos P. Theologides; Petros G. Savva; Costas N. Costa (pp. 54-61).

Display Omitted▶ Composition of support affects behaviour of Pd–Cu catalysts towards NO₃⁻/H₂/O₂. ▶ NH₄⁺ selectivity decreases by 3 times when 4% O₂ is added in the feed. ▶ 20 times less NH₄⁺ is obtained when increasing liquid flow from 2 to 6mL/min. ▶ 5 times less NH₄⁺ is obtained when input CNO₃⁻ increases from 10 to 100mg/L. ▶ The presence of Cl⁻ ions in the feed slightly increases catalysts activity.The selective catalytic reduction of nitrates (NO₃⁻) in water mediums towards N₂ formation by the use of H₂ and in the presence of O₂ (air) in the gas feed has been investigated under a continuous flow process over Pd–Cu supported on various mixed metal oxides, xwt.% M_xO_y/γ-Al₂O₃ (M_xO_y=CeO₂, MgO, Mn₂O₃, Cr₂O₃, Y₂O₃, MoO₂, Fe₂O₃ and TiO₂). It is demonstrated for the first time that a remarkable improvement of both catalysts activity and N₂ reaction selectivity can be achieved when increasing the liquid flow rate in the continuous flow process. In particular, it was found that NO₃⁻ reduction rates up to more than two times higher and NH₄⁺ selectivity values up to twenty times lower can be obtained when increasing the liquid flow rate from 2 to 6mL/min. Moreover, it was proven for the first time, in a continuous flow process, that the presence of oxygen (or air) has a remarkable positive effect on the reaction's selectivity towards nitrogen. The reaction's selectivity towards NH₄⁺ can be decreased by up to three times when 20vol.% air is added in the gas feed of the NO₃⁻/H₂ continuous flow reaction. The Pd–Cu clusters supported on TiO₂-, CeO₂- and MgO-coated γ-Al₂O₃ spheres showed the best catalytic behaviour compared with the rest of supports examined, both in the presence and in the absence of oxygen in the reducing feed gas stream. In addition, it was found that the initial concentration of nitrates in the liquid feed can significantly affect catalysts activity and reaction's selectivity. A positive apparent reaction order towards nitrates of 0.9 was calculated on Pd–Cu/TiO₂/Al₂O₃.

Keywords: Catalytic denitrification; Nitrates reduction; Nitrates removal; Supported Pd–Cu; CSTR

Effects of Pd on enhancement of oxidation activity of LaBO₃ (B=Mn, Fe, Co and Ni) pervoskite catalysts for pollution abatement from natural gas fueled vehicles by Hessam Ziaei-Azad; Abbasali Khodadadi; Parvaneh Esmaeilnejad-Ahranjani; Yadollah Mortazavi (pp. 62-70).

Display Omitted▶ Pd facilitates reducibility of M in LaMPd_0.05O₃ (M=Mn, Fe, Co and Ni) pervoskites. ▶ Pd effect is more pronounced for CO oxidation as compared to that for CH₄. ▶ LaFePd_0.05O₃ catalyst shows the highest activity for CO and CH₄ oxidation. ▶ Pd addition to LaFeO₃ lowers T₉₀ of CO and CH₄ by 175 and 52°C respectively.The effect of Pd on activity enhancement of perovskite catalysts for oxidation of CH₄ and CO emitted from natural-gas fueled vehicles is investigated using a synthetic stoichiometric exhaust gas mixture. Various LaBO₃ and LaBPd_0.05O₃ (B=Mn, Fe, Co and Ni) perovskite-type nanocatalysts were prepared via a solution combustion synthesis, calcined at 700°C for 5h, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET specific surface area measurement, H₂ temperature programmed reduction (TPR) and O₂ temperature programmed desorption (TPD). XRD results, confirms the presence of PdO in Pd-containing samples, which is highly active for CO and CH₄ oxidation. TPR and TPD results show that Pd significantly facilitates the reducibility of B in LaBPd_0.05O₃ pervoskites and enhances the mobility of lattice oxygen in the prepared samples, which results in activity enhancement for Pd-containing catalysts. Oxidation activity results reveal that Pd effect is more pronounced for CO oxidation as compared to that for CH₄, probably due to the Pd transition from PdO to metallic Pd and/or its incorporation into the pervoskite structure occurred at elevated temperatures, which both seem to reduce its activity. Among the prepared samples, LaFePd_0.05O₃ catalyst shows the highest activity for CO and CH₄ oxidation, T₉₀ of which occur at 165 and 558°C, 191 and 40°C lower than that for LaFeO₃ respectively.

Keywords: Palladium; Perovskite catalysts; Natural gas fueled vehicles

Titania supported platinum catalyst with high electrocatalytic activity and stability for polymer electrolyte membrane fuel cell by Sheng-Yang Huang; Prabhu Ganesan; Branko N. Popov (pp. 71-77).

Display Omitted▶ Pt particles of 3–5nm can be deposited on mesoporous TiO₂. ▶ Pt/TiO₂ and Pt/C catalysts exhibit comparable fuel cell activity. ▶ Pt/TiO₂ shows high activity and stability after accelerated durability test. ▶ Pt/TiO₂ can be a promising catalyst for PEM fuel cells for automotive applications.Titania supported Pt electrocatalysts (Pt/TiO₂) were synthesized and investigated as alternative cathode catalysts for polymer electrolyte membrane fuel cells (PEMFCs). Transmission electron microscope (TEM) images revealed uniform distribution of Pt nanoparticles ( d_Pt=3–5nm) on the TiO₂ support. The Pt/TiO₂ electrocatalyst showed comparable activity to that of a commercial Pt/C catalyst (TKK) in fuel cell studies. The fuel cell accelerated stress test (AST) for catalysts demonstrated similar stability for Pt/TiO₂ and Pt/C. In-house developed accelerated durability test (ADT, continuous potential cycling between 0.6 and 1.4V) in half-cell condition indicated nearly ten-fold higher ORR activity (1.20mAcm⁻²) when compared to the Pt/C catalyst (0.13mAcm⁻²). The Pt/C catalyst showed no activity in fuel cell testing after 2000 potential cycles due to severe carbon corrosion, Pt dissolution, and catalyst particle sintering. Conversely, the Pt/TiO₂ electrocatalyst showed only a small voltage loss (0.09V at 0.8Acm⁻²) even after 4000 cycles. Furthermore, the ADT results showed excellent stability for the Pt/TiO₂ electrocatalysts at high potentials in terms of minimum loss in the Pt electrochemical surface area (ECSA). The high stability of the Pt/TiO₂ electrocatalyst synthesized in this investigation offers a new approach to improve the reliability and durability of PEM-based fuel cell cathode catalysts.

Keywords: Titania; Cathode catalyst support; Corrosion resistance; Oxygen reduction reaction; Proton exchange membrane fuel cell

Structure properties and catalytic performance in methane combustion of double perovskites Sr₂Mg1−_xMn_xMoO6−_δ by Chen Li; Wendong Wang; Ning Zhao; Yuanxu Liu; Bo He; Fengchun Hu; Chusheng Chen (pp. 78-84).

Display Omitted▶ SOFC anode materials Sr₂Mg1−_xMn_xMoO6−_δ prove active catalysts for CH₄ combustion. ▶ Catalytic property depends on degree of Mn substitution in Sr₂Mg1−_xMn_xMoO6−_δ. ▶ Optimal Mn substitution x=0.5 leads to the highest activity for Sr₂Mg_0.5Mn_0.5MoO6−_δ. ▶ Higher oxygen vacancy concentration promotes activity for Mn-containing catalysts. ▶ Catalytic performance correlates with Mn-relating surface lattice oxygen species.The double perovskite oxides Sr₂Mg1−_xMn_xMoO6−_δ ( x=0, 0.2, 0.5, 0.8 and 1), formerly applied as anode materials for solid oxide fuel cells, were investigated as catalysts for the methane combustion. The mixed oxides were prepared by sol–gel procedures, followed by annealing under reducing atmosphere of 5% H₂ in nitrogen. The structure properties of these oxides were characterized in detail by X-ray diffraction, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. The catalytic property was strongly influenced by the Mn substitution and the optimized activity was observed for Sr₂Mg_0.5Mn_0.5MoO6−_δ. The relation between catalytic performance and degree of Mn substitution was examined with regard to the structure and surface characteristics of the mixed oxides, which was discussed in view of the presence of oxygen vacancies and may be correlated with the Mn-relating surface lattice oxygen species.

Keywords: Catalytic combustion; Methane; Double perovskites; SOFC anode materials; Sr; ₂; Mg; 1−; _x; Mn; _x; MoO; 6−; _δ

Optimization of H₂O₂ use during the photocatalytic degradation of ethidium bromide with TiO₂ and iron-doped TiO₂ catalysts by J. Carbajo; C. Adán; A. Rey; A. Martínez-Arias; A. Bahamonde (pp. 85-93).

Display Omitted▶ EtBr is eliminated by heterogenous photocatalysis with TiO₂ and iron-doped TiO₂. ▶ Acid/basic properties affected by iron presence are essential to EtBr photodegradation. ▶ Optimization of the use of H₂O₂ improves the properties for complete mineralization of EtBr.A series of nanosized iron-doped titania catalysts has been used for the photocatalytic degradation of ethidium bromide (EtBr) with oxygen. The study shows that EtBr surface adsorption is most favored over basic titania surfaces such as those present in undoped TiO₂ and Fe–TiO₂ with low iron content. This fact is shown to affect strongly the photocatytic mechanism of EtBr degradation. Based on EtBr adsorption and photocatalytic activity analyses, a titania catalyst with an iron content of 0.7wt.% has been selected for subsequent studies using H₂O₂ as oxidant. Parameters as reaction pH and initial hydrogen peroxide concentration were analyzed to establish optimum operating conditions. It is shown that a new strategy based on dosing H₂O₂ in a controlled way could minimize radical self-scavenging reactions and improves final EtBr mineralization degree. Finally, the stability and durability of catalyst/activity have been examined through five consecutive cycles of H₂O₂ dosing. A constant activity level is maintained during at least four consecutive cycles in which total EtBr and 80% of Total Organic Carbon conversion is achieved.

Keywords: Photocatalysis; Ethidium bromide; Nanostructured iron-doped TiO; ₂; H; ₂; O; ₂; dosage

Steam and CO₂ reforming of ethanol over Rh/CeO₂ catalyst by Adriana M. da Silva; Kátia R. de Souza; Gary Jacobs; Uschi M. Graham; Burtron H. Davis; Lisiane V. Mattos; Fábio B. Noronha (pp. 94-109).

Display Omitted▶ Rh/CeO₂ high surface area catalyst exhibited better stability in SR of ethanol, with no carbon formation. ▶ DRIFTS experiments revealed that Rh carbonyl bands were quite s, showing no carbon deposits. ▶ Improved stability is likely attributed to a greater fugacity of available O from the support. ▶ O adatoms or surface OH groups from the support takes part on the carbon removal mechanism.The performance of ceria supported Rh catalysts prepared with high and low surface areas for steam reforming and dry reforming of ethanol was investigated. According to results of diffuse reflectance infrared Fourier transform spectroscopy of both reactions, dissociative adsorption of ethanol over ceria gives rise to ethoxy species and bridging OH groups. Oxidation of ethoxy species proceeds by addition of O provided by the support from species such as Type II bridging OH groups (i.e., steam reforming) or O adatoms (e.g., CO₂ reforming). Rh promotes demethanation of acetate to carbonate and the steam/dry reforming of CH_x species.Catalyst deactivation occurs from the deposition of carbon on the catalysts during both reactions. However, no carbon formation is observed on the Rh/CeO₂ high surface area catalyst during steam reforming due to a higher surface fugacity of O from species adsorbed on the support that react to remove carbon.

Keywords: Hydrogen production; CO; ₂; reforming of ethanol; Steam reforming of ethanol; Rh/CeO; ₂; catalyst; Carbon formation

Spatially resolving SCR reactions over a Fe/zeolite catalyst by Jin-Yong Luo; Xuxian Hou; Prasanna Wijayakoon; Steven J. Schmieg; Wei Li; William S. Epling (pp. 110-119).

Display Omitted▶ First ever spatial resolution of SCR reactions along a monolith. ▶ If NO>NO₂, fast SCR is followed by standard SCR, i.e. reactions are in series. ▶ If NO2, fast SCR and NO₂ SCR occur in parallel.There have been several recent reports regarding the spatial resolution of gas species in monolith-supported automobile exhaust catalysts, with examples including characterization of DOCs (diesel oxidation catalysts) and LNTs (lean NO_x traps). However, spatially resolving gas concentrations in NH₃-SCR (selective catalytic reduction) applications is limited due to the difficulty in ppm-level NH₃ detection in the presence of percent levels of water and N₂ using mass spectrometry. In this study, a gas-phase FT-IR analyzer was used for the first time to spatially resolve gas concentrations in a monolith-supported SCR catalyst. The reactions analyzed include standard SCR, fast SCR and SCR with NO₂. The results show that the three SCR reactions proceed at significantly different rates, especially at temperatures below 300°C, and can be correlated to the amount of catalyst used. For example, the catalyst lengths needed to achieve 80% NO_x conversion at 300°C are 2.4, 1.2 and 0.5cm for conditions that meet the standard SCR, NO₂-SCR and fast SCR reaction stoichiometries, respectively. For the standard SCR reaction, kinetic analysis, and spatially resolved NO oxidation and SCR results consistently indicate that the rate-determining step is NO oxidation. NH₃ has an inhibition effect, as it suppresses NO oxidation by competitive adsorption on the active sites. At 300°C, the outlet NO_x conversion is not limited by the reaction kinetics, but by insufficient NH₃ supply, since part of the NH₃ is oxidized by O₂. Compared with 300°C, higher NO_x conversions are attained at 400 or 500°C, which is due to significantly enhanced NO oxidation, and the resulting increase in NH₃ reacting with NO_x via SCR rather than O₂ via NH₃ oxidation. For NO₂-SCR, a considerable amount of N₂O was formed at 250°C but decreased with increasing temperature. The decreased N₂O is due to improved selectivity in the NO₂-SCR to N₂, as well as N₂O decomposition at the back part of the catalyst at high temperature. Finally, different SCR reaction patterns were identified when testing with NO:NO₂=3:1 and 1:3. For NO:NO₂=3:1, the SCR reactions proceed in series, namely through the fast reaction first, followed by standard SCR. The fast SCR and NO₂-SCR reactions proceed in parallel for NO:NO₂=1:3. The results indicate that if NO₂ is the limiting reactant, fast SCR dominates, but if excess NO₂ is available, the NO₂ SCR reaction can proceed in parallel.

Keywords: Key words; Spatial resolution; NH; ₃; -SCR; Fe-zeolite; standard SCR; Fast SCR; NO; ₂; SCR; Reaction kinetics

Highly active and durable Bi₂O₃/TiO₂ visible photocatalyst in flower-like spheres with surface-enriched Bi₂O₃ quantum dots by Jian Zhu; Shaohua Wang; Jinguo Wang; Dieqing Zhang; Hexing Li (pp. 120-125).

Display Omitted▶ A novel flower-like Bi₂O₃/TiO₂ was prepared by a facile solvothermal alcoholysis. ▶ The flower-like structure enhanced light absorption via multiple light reflections. ▶ Surface-enriched Bi₂O₃ quantum dots promoted photosensitizing effect. ▶ The Bi₂O₃/TiO₂ displayed strong interaction between Bi₂O₃ and TiO₂. ▶ The Bi₂O₃/TiO₂ exhibited high activity and strong durability in photocatalysis.The flower-like Bi₂O₃/TiO₂ visible photocatalyst with surface enrichment of Bi₂O₃ quantum dots was synthesized using a facile solvothermal process, which exhibited much higher activity than the Bi₂O₃/TiO₂-IM prepared by impregnation method and the Bi₂O₃/TiO₂-GR obtained by crushing the flower-like Bi₂O₃/TiO₂. The high activity could be attributed to the enhanced light absorbance via multiple reflections in flower-like structure, the enhanced photosensitizing effect of the surface enriched Bi₂O₃ quantum dots and the strong interaction between Bi₂O₃ and TiO₂. Moreover, the Bi₂O₃/TiO₂ exhibited strong durability and could be reused for more than 10 times, which could be attributed to the high hydrothermal stability of the flower-like structure and the inhibition of Bi₂O₃ leaching owing to its strong interaction with TiO₂.

Keywords: Flower-like Bi; ₂; O; ₃; /TiO; ₂; spheres; Surface enriched Bi; ₂; O; ₃; quantum dots; Visible light photocatalyst; Degradation of; p; -chlorophenol

Remarkable improvement of visible light photocatalysis with PANI modified core–shell mesoporous TiO₂ microspheres by Gaozu Liao; Shuo Chen; Xie Quan; Yaobin Zhang; Huimin Zhao (pp. 126-131).

Display Omitted▶ The core–shell mesoporous structure of PANI/M-TiO₂ improved the light absorption. ▶ The heterojunction between TiO₂ and PANI facilitated the separation of carriers. ▶ Enhanced photocatalysis was achieved via PANI modified core–shell mesoporous TiO₂.PANI modified core–shell mesoporous TiO₂ (PANI/M-TiO₂) with efficient photocatalytic capability under visible light irradiation was fabricated by hydrothermal method and chemisorption approach. The nitrogen adsorption–desorption characterization indicated that the specific surface area of mesoporous M-TiO₂ was 2.8 times as great as that of P25, which resulted in the increased uptake of PANI molecule on the surface of M-TiO₂. Environmental scanning electron microscopy and transmission electron microscopy images demonstrated that the PANI/M-TiO₂ possessed a unique core–shell structure, which allowed multiple reflection or scattering of light in the photocatalyst and led to the increase of optical path length subsequently. Both the increased uptake of PANI molecules and optical path length in photocatalyst contributed to enhance the visible light absorption. The UV–vis diffuse reflectance spectra confirmed that the optical absorption for PANI/M-TiO₂ was more intensive than that for PANI modified TiO₂ nanoparticle (PANI/NP-TiO₂) in the visible light region. The intensive visible light absorption and effective charge separation owing to the heterojunction built between TiO₂ and PANI lead to remarkable improvement of visible light photocatalysis. The pseudo-first-order kinetic constant of photocatalytic degradation of rhodamine B and 4-chlorophenol under visible light irradiation with 6% PANI/M-TiO₂ was 5.04 and 2.03 times as great as that with PANI/NP-TiO₂ respectively, showing the advantage of the unique core–shell mesoporous structure in the PANI/M-TiO₂ for efficient photocatalysis.

Keywords: Optical path length; Heterojunction; Visible light absorption; Photocatalytic capability

Photocatalytic hydroxylation of benzene to phenol over titanium oxide entrapped into hydrophobically modified siliceous foam by Guan Zhang; Jaeseon Yi; Jongmin Shim; Jinwoo Lee; Wonyong Choi (pp. 132-139).

Display Omitted▶ Titania entrapped into hydrophobically modified mesocellular siliceous foam was synthesized. ▶ Selective photocatalytic conversion of benzene to phenol was achieved. ▶ By modifying the hydrophobicity of catalyst the selectivity and phenol yield markedly increased. ▶ The catalyst serves as an efficient photocatalyst for selective photocatalytic oxidation.The selective photocatalytic conversion of benzene to phenol was achieved on titania incorporated in hydrophobically modified mesocellular siliceous foam (MCF). Titanium oxide nanoparticles entrapped into mesocellular siliceous foam (TiO₂@MCF) were prepared by “co-condensation” method using block copolymer as a template. TiO₂@MCF was further modified by surface organo-grafting with silylation agent to make it hydrophobic (TiO₂@MCF/CH₃) and the grafted organic functional groups on the surface of TiO₂ were selectively removed by post UV-irradiation to obtain the catalyst (TiO₂@MCF/CH₃/UV) that has a higher selective activity for benzene oxidation. By modifying the hydrophobicity of the mesoporous siliceous cage environment, both the adsorption of reactants (benzene) and the desorption of the desired products (phenol) on photocatalytic sites can be facilitated with an increase in selectivity and yield of phenol production. The titania nanoparticles incorporated into MCF cage were characterized by X-ray diffraction, nitrogen adsorption–desorption, high-resolution transmission electron microscopy, energy-dispersive X-ray analysis, and UV–visible diffuse reflectance spectroscopy. The hydrophobic modification of the catalysts was confirmed by Fourier transform infrared spectroscopy, water contact angle measurement, and thermo-gravimetric analysis. The adsorption isotherms of benzene and phenol on various catalysts suspended in aqueous solution were measured to investigate the effect of hydrophobic MCF cage. The hydrophobically modified TiO₂@MCF/CH₃/UV sample showed the highest selectivity and yield for the photocatalytic hydroxylation of benzene to phenol in aqueous solution. This could serve as an efficient and green photocatalyst for the selective oxidative conversion of a hydrophobic reactant to a hydrophilic product.

Keywords: Green synthesis; Titania; Mesocellular siliceous foam; Phenol synthesis; Selective oxidation

Photocatalytic degradation and detoxification of o-chloroaniline in the gas phase: Mechanistic consideration and mutagenicity assessment of its decomposed gaseous intermediate mixture by Taicheng An; Lei Sun; Guiying Li; Yanpeng Gao; Guangguo Ying (pp. 140-146).

.Display Omitted▶ Two intermediates, chlorobenzene and phenol, were found in the gas phase. ▶ Trace solid phenol and o-dihydroxybenzene were found on the surface of TiO₂. ▶ Mutagenic toxicity of gaseous intermediates decreased with increasing the degradation time. ▶ The gaseous intermediates have no mutagenic activity after 300min degradation. ▶ The photocatalytic technology has excellent capability to decontaminate o-ClA efficiently.The photocatalytic degradation of o-chloroaniline ( o-ClA) on a TiO₂ thin film was investigated using o-ClA as a model of semi-volatile organic compounds. The degradation efficiencies of o-ClA with ca. 4300μgL⁻¹ were up to 99.0% within a 300min illumination. The degradation kinetics of o-ClA followed a pseudo first-order reaction. Two intermediates, chlorobenzene and phenol, were found in the gas phase, and trace phenol and o-dihydroxybenzene were also detected on the surface of the TiO₂ film. Based on the identified intermediates and the theatrical calculation data of the frontier electron densities and point charges, a photocatalytic degradation mechanism was proposed tentatively. When tested using SOS/umu and Ames assay, neither the o-ClA nor the gaseous intermediates at different degradation times presented mutagenic activity to strain TA1535/pSK1002(−S9) as well as TA98(±S9) and TA100(−S9) at all tested doses. However, o-ClA at high doses did show weak mutagenic activity to strain TA1535/pSK1002 in SOS/umu assay and to strain TA100 in Ames assay with S9 metabolic activation. However, the mutagenic toxicity of the gaseous intermediates decreased rapidly as the degradation time increased, and when tested using both mutagenicity assays, no mutagenic activity was seen after 300min. Therefore, by combining mechanistic consideration with mutagenicity assessment, photocatalytic technology was found to be an effective detoxification method for gaseous aromatic amines.

Keywords: Key words; Volatile organic compounds; O; -chloroaniline; Photocatalytic degradation; Detoxification; Degradation mechanism

Fabrication and photocatalytic performance of a Zn_xCd1−_xS solid solution prepared by sulfuration of a single layered double hydroxide precursor by Xin Xu; Ruijuan Lu; Xiaofei Zhao; Sailong Xu; Xiaodong Lei; Fazhi Zhang; David G. Evans (pp. 147-156).

Display Omitted▶ A series of Zn_xCd1−_xS solid solution nanoparticles have been synthesized. ▶ The Zn_xCd1−_xS nanoparticles were arranged regularly inside a matrix of alumina. ▶ Their light absorption properties in the visible region varied with Zn content. ▶ They showed excellent photocatalytic activity for degradation of methylene blue.Zn_xCd1−_xS nanoparticles have been successfully synthesized by reaction of a single precursor – a Zn,Cd,Al-containing layered double hydroxide (ZnCdAl–LDH) – with H₂S. The Zn_xCd1−_xS nanoparticles are homogeneously distributed within the confinement of an amorphous alumina matrix, in marked contrast to the aggregation that occurs with Zn_xCd1−_xS prepared by conventional coprecipitation. The photoactivities of the Zn_xCd1−_xS nanoparticles for methylene blue (MB) photodegradation increased with decreasing Zn mole fraction x, and the best performance was achieved with a Zn mole fraction of 0.20. The Zn_xCd1−_xS materials exhibited significantly better photocatalytic performance than Zn_xCd1−_xS with the same composition obtained either by a coprecipitation method or by sulfuration of a physical mixture of Zn,Al–LDH and Cd,Al–LDH precursors. This suggests that the ordered arrangement on an atomic level of the metal cations within the LDH layers leads to a homogeneous array structure of the Zn_xCd1−_xS solid solution, which suppresses the recombination of photoexcited electrons and holes, leading to improved photocatalytic activity. Our method provides a way to fabricate new types of chalcogenide semiconductor photocatalysts which are active under illumination by visible light.

Keywords: ZnS; CdS; Layered double hydroxide precursor; Photocatalysis; Band gap; ESR

Low bias photoelectrocatalytic (PEC) performance for organic vapour degradation using TiO₂/WO₃ nanocomposite by Yuan Liu; Changsheng Xie; Huayao Li; Hao Chen; Yichuan Liao; Dawen Zeng (pp. 157-162).

Display Omitted▶ A novel PEC flat-plate type device suitable for the gas-phase application is supplied. ▶ TiO₂/WO₃ composite needs much lower bias than TiO₂ for the activity enhancement. ▶ The absorption wavelength range of the TiO₂/WO₃ composite, compared with WO₃, is redshifted. ▶ The explanation based on the transportation of the electrons is proposed.In this study, a novel photoelectrocatalytic (PEC) flat-plate type device used in the gas-phase was fabricated by the technology of screen printing. The TiO₂/WO₃ nanocomposite (2:8 in mole ratio) was prepared by a simple milling-anneal method and printed onto the device. The obtained device was attempted to investigate the PEC performance by applying low biases for degrading the volatile organic compounds (VOCs). The apparent pseudo-first-order kinetic model was used to describe the degradation process. The results showed that the applied low bias had a distinct enhancement effect on the degradation activity compared to photocatalytic (PC) degradation. The PEC degradation rate under UV-light (365nm) irradiation by applying only 0.2V bias was about 12.28×10⁻³min⁻¹, which was 2.42 times of PC degradation rate. Under the blue-light (475nm) irradiation, the composite still had good degradation efficiency and the rate constant was about 2.6×10⁻³min⁻¹. Furthermore, the explanation was proposed that the degradation activity of TiO₂/WO₃ composite could show obviously enhancement for gas-phase PEC process by applying bias at a very low level, compared to pure TiO₂.

Keywords: Low bias; Gas-phase; Photoelectrocatalytic; Nanocomposite; TiO; ₂; WO; ₃

Effects of O₂, CO₂ and H₂O on NO_x adsorption and selective catalytic reduction over Fe/ZSM-5 by Terris T. Yang; Hsiaotao T. Bi; Xingxing Cheng (pp. 163-171).

Display Omitted▶ NO_x adsorption on Fe/ZSM-5 catalyst is promoted by O₂. ▶ H₂O has little effect on NO_x adsorption but enhances reactivity of Fe/ZSM-5. ▶ CO₂ negatively impacts on NO_x adsorption but little effect on reactivity of Fe/ZSM-5. ▶ O₂ significantly reduces NO_x conversion in Fe/ZSM-5–propylene system. ▶ SO₂ seriously poisons Fe/ZSM-5 catalyst.The adsorption performance and catalytic activity of Fe/ZSM-5 for the selective catalytic reduction (SCR) of NO_x with propylene were studied in a fixed bed reactor using model flue gases. The Fe/ZSM-5 catalyst showed reasonable NO_x adsorption capacity, and the adsorption performance is closely related to the particle size and the structure of the catalyst support. The increase of O₂ concentration significantly enhanced the adsorption of NO_x on Fe/ZSM-5, and CO₂ in the flue gas exhibited certain negative impact on the adsorption capacity, while H₂O showed little effect. HC-SCR experiments showed that Fe/ZSM-5 catalyst was sensitive to the reaction temperature and space velocity, and exhibited acceptable activity when O₂ concentration was controlled at a low level. Water in the flue gas was found to slightly enhance the reactivity of Fe/ZSM-5, while the presence of CO₂ showed little effect.

Keywords: NO; _x; Adsorption; Reduction; Fe/ZSM-5; Propylene; Fixed bed

Photocatalytic degradation of humic acids and landfill leachate using a solid industrial by-product containing TiO₂ and Fe by R. Poblete; E. Otal; L.F. Vilches; J. Vale; C. Fernández-Pereira (pp. 172-179).

Display Omitted▶ A by-product containing Ti and Fe was used as catalyst for landfill leachate degradation. ▶ Factors affecting yield were obtained by a fractional factorial design. ▶ Probably Fe(III) complexes have a synergistic effect on the catalytic activity of TiO₂.Landfill leachates contain a large number of recalcitrant compounds that make it unsuitable for conventional waste water treatment. This work has studied the effectiveness of a treatment method for the degradation of landfill leachates, based on a photocatalytic advanced oxidation process. The process consists of a photocatalytic treatment under UV radiation at a maximum emission wavelength of 365nm using a solid by-product obtained from the titanium dioxide production industry, which contains TiO₂ and Fe(III) as a catalyst. The product which has been used in these kinds of applications for the first time has also been compared with commercial TiO₂. A multifactorial design was used to analyze the influence of significant factors that affect degradation yield such as the type of catalyst, type of oxidizable compound, catalyst loading, reaction time and pH. In addition to a landfill leachate, we have studied the abatement of some specific organic compounds, such as p-cresol and humic acids that are regularly present in landfill leachates and are considered refractory compounds. The results demonstrated that the application of this by-product resulted in a higher level of pollutant degradation as compared to commercial TiO₂.

Keywords: Factorial design; Landfill leachate; Photocatalysis; TiO; ₂; Waste recycling

Parametric study of propene oxidation over Pt and Au catalysts supported on sulphated and unsulphated titania by Alexandre Baylet; Chloé Capdeillayre; Laurence Retailleau; Jose Luis Valverde; Philippe Vernoux; Anne Giroir-Fendler (pp. 180-189).

Display Omitted▶ Pt and Au supported on sulphated or unsulphated TiO₂ were tested for the catalytic oxidation of C₃H₆. ▶ For the Pt catalysts, the rate determining step was oxygen adsorption. ▶ For the Au catalysts the limiting step was concluded to be the propene dissociation.The influence of the experimental parameters such as total flow rate, partial pressure of O₂ and C₃H₆, the nature of the metal, platinum or gold, and the surface treatment of the titania support, sulphated or not, have been investigated on the reaction of propene oxidation. Analysis including XPS, ICP and TEM were carried out in order to characterize the platinum and gold particles and sulphate compounds (oxidation degree, content, morphology). The XPS analysis revealed the presence of Pt²⁺ and Au° species at the catalyst surface. The TEM micrographs indicated Pt particles less than 5nm and Au particle size composed between 6 and 15nm with a heterogeneous dispersion. For the Pt catalyst, catalytical testing displayed that the presence of sulphate compounds at the support surface did not influence the partial pressure order of O₂ and C₃H₆, 1.5 and 0, respectively. For the Au catalyst, the acidity of the support modified the kinetics by decreasing the partial pressure order from 0.5 to −0.7 for O₂ and from 0 to −0.7 for C₃H₆. In the steady state conditions, a simple power rate law model was adopted to determine the rate constant and the activation energy; Ea varying between 20 and 50kJmol⁻¹. For the Pt catalysts, the rate determining step was oxygen adsorption whereas for the Au catalysts the limiting step was concluded to be the propene dissociation. The catalytic activity was not linked to the specific surface area or the metal content but could be attributed to the nature of the metal, the sulphated support and to the particle oxidation degree and, to a less extent, the particle size.

Keywords: Platinum; Gold; Titania; Sulphate; Partial pressure order; Propene; Oxygen

An operando IR study of the unburnt HC effect on the activity of a commercial automotive catalyst for NH₃-SCR by Irene Malpartida; Olivier Marie; Philippe Bazin; Marco Daturi; Xavier Jeandel (pp. 190-200).

Display Omitted▶ The unburnt HCs traces decrease the DeNO_x efficiency of Fe-ZSM5 for SCR-NH₃ ▶ C₁₀H₂₂ and C₇H₈ hinder the reaction by pore blocking of coke deposition ▶ NO_x conversion drop is also associated to a lower adsorbed NH₄⁺ under steady state ▶ C₁₀H₂₂ is the most inhibiting compound due to a competitive adsorption with ammonia on the active sites.A commercial zeolite-based catalyst for NO_x removal via ammonia SCR has been studied in a synthetic flow very close to a real automotive exhaust mixture. Particular attention has been paid to reproduce effective temperatures and space velocities. The impact of the hydrocarbon presence towards the NH₃-SCR efficiency has been investigated through the use of a mixture of representative hydrocarbons, i.e. propene, toluene and decane. It has been found that both decane and toluene produce a carbonaceous deposit, partially hindering the reaction by pore blocking. However, it also appears that decane is the most inhibiting compound for the deNO_x activity due to a competitive adsorption with ammonia on the active sites, notably at low temperature.

Keywords: DeNO; _x; NH; ₃; -SCR; Commercial Fe-containing ZSM-5 zeolite; Hydrocarbons deactivation; Propene; Toluene; Decane; Operando-IR-MS; Catalyst at work

Superabsorbent hydrogels for cobalt nanoparticle synthesis and hydrogen production from hydrolysis of sodium boron hydride by Nurettin Sahiner; Ozgur Ozay; Erk Inger; Nahit Aktas (pp. 201-206).

Display Omitted▶ In situ Co metal nanoparticle synthesis inside hydrogels. ▶ Hydrogel reactor for hydrogen production. ▶ Environmentally benign hydrogel–Co composites. ▶ Hydrogel–Co for the hydrolysis of NaBH₄.Polymeric hydrogels derived from 2-acrylamido-2-methyl-1-propansulfonic acid (AMPS) were utilized in the preparation of cobalt (Co) metal nanoparticles and used as a composite–catalyst system in hydrogen generation from the hydrolysis of NaBH₄. The embedded Co nanoparticles in the p(AMPS) networks are on the order of 100nm. It was demonstrated that the p(AMPS)–Co composite system was very effective in the production of hydrogen from alkali aqueous sodium boron hydride solutions. The effect of various parameters such as the initial concentration of NaBH₄, the amount of catalyst and temperature on the hydrolysis reaction was evaluated. The activation energy for hydrogen production by Co particles was found to be 38.14kJmol⁻¹; while the activation enthalpy was 35.46kJmol⁻¹.

Keywords: Hydrogen production; Hydrogel nanoreactor; Composite–catalysts; Cobalt nanoparticles; Hydrolysis

Manganese-promoted cobalt oxide as efficient and stable non-noble metal catalyst for preferential oxidation of CO in H₂ stream by Qinghong Zhang; Xianhong Liu; Wenqing Fan; Ye Wang (pp. 207-214).

.Display Omitted▶ Modification by MnO_x enhanced catalytic performances of Co₃O₄ for CO-PROX in H₂. ▶ MnO_x–Co₃O₄ showed higher activity, selectivity and stability in CO-PROX at ∼100̊C. ▶ MnO_x modification increased the amounts of reactive oxygen species and adsorbed CO. ▶ Presence of MnO_x accelerated the regeneration ability of the reduced catalyst by O₂.The modification by MnO_x significantly enhanced the activity and stability of Co₃O₄ for the preferential oxidation of CO in H₂-rich stream. The MnO_x-promoted Co₃O₄ catalyst with a Mn/Co molar ratio of 1/8 exhibited the best performance; CO conversion was 56% at 40°C and increased to >90% as the temperature was raised to >75°C. This catalyst could provide 100% CO conversion at 125–175°C. CO conversions of 97% and 100% remained unchanged for 100h at 100 and 125°C, respectively, whereas the deactivation was observed over Co₃O₄ alone. Our characterizations using XRD, XPS and TEM indicated that the modification of Co₃O₄ with MnO_x caused the formation of smaller Mn_xCo3−_xO₄ solid-solution particles. The O₂-TPD, CO-TPD, and pulse reaction studies suggest that the incorporation of MnO_x into Co₃O₄ increased the amounts of reactive oxygen species and adsorbed CO species over catalyst surfaces and enhanced the regeneration ability of the reduced catalyst by O₂. All these enhancements are proposed to be responsible for the improved catalytic performance of the MnO_x-promoted Co₃O₄.

Keywords: Carbon monoxide; Preferential oxidation; High-purity hydrogen; Cobalt oxide; Manganese oxide

A Mössbauer and structural investigation of Fe-ZSM-5 catalysts: Influence of Fe oxide nanoparticles size on the catalytic behaviour for the NO-SCR by C₃H₈ by Giuseppe Fierro; Giuliano Moretti; Giovanni Ferraris; Giovanni B. Andreozzi (pp. 215-223).

Display Omitted▶ In over-exchanged Fe-ZSM-5 catalysts at high Fe loading no bulk Fe oxides but nanosized Fe_xO_y species, undergoing a superparamagnetic behaviour, are formed. ▶ In the two Fe-ZSM-5 catalysts the Fe oxide nanoparticles are varying in size and the relative abundance of larger/smaller nanoparticles is different ▶ Larger Fe_xO_y nanoparticles appear to be prevailing in the catalyst at higher Fe loading. ▶ The larger Fe_xO_y nanoparticles are characterized by a very low activity for the NO-SCR reaction. ▶ The larger Fe_xO_y nanoparticles enhance the hydrocarbon total combustion to CO₂, thus limiting the formation of the undesired CO along the NO-SCR reaction.In this work some results concerning a spectroscopic and structural characterization of two Fe-ZSM-5 (Si/Al=25) catalysts (Fe=1.31wt% and 8.40wt%), prepared by the ion-exchange method, are reported. The final catalysts, obtained by calcination in air at 773K, were investigated by Mössbauer spectroscopy as well as by XRD, DRS and porosimetry together with the H-ZSM-5 parent material. In consequence of the treatment at high temperature in air, iron oxide species were formed in the Fe-ZSM-5 catalysts. Surprisingly, in spite of the rather high Fe loading, in both catalysts no large, or bulk, Fe oxide particles, which should be segregated at the external surface of the zeolite, have been found. On the contrary the iron oxide species were only in the form of nanoparticles, even in the largely over-exchanged preparation at high Fe content. The Fe oxide nanoparticles are varying in dimension and, depending on their size, they result to be differently located in the zeolite structure. The smaller Fe oxide-like nanoparticles, which prevails in the catalyst with minor Fe content (Fe=1.31wt%), are mainly confined inside the micropores whereas the Fe oxide-like nanoparticles characterized by a larger size, which appear to be more abundant in the catalyst at higher Fe loading (Fe=8.40wt%), are located on the zeolite external surface. The catalytic activity and selectivity for the SCR of NO by propane are remarkably influenced by the size of the Fe oxide nanoparticles. The catalyst with less Fe content, characterized by a larger amount of smaller nanosized Fe_xO_y like-species, is more active but less selective to CO₂ than the excessively over-exchanged catalyst. This suggests that the Fe_xO_y nanoparticles larger in size, prevailing in the catalysts at higher Fe content, contribute very little, or not at all, to the catalytic activity but markedly improve the selectivity to CO₂.

Keywords: Key words; Fe-ZSM-5 catalysts; Nanosized iron oxide species; XRD and textural characterization; DRS and Mössbauer spectroscopy; SCR of NO by propane

Role of pore structure in the deactivation of zeolites (HZSM-5, Hβ and HY) by coke in the pyrolysis of polyethylene in a conical spouted bed reactor by G. Elordi; M. Olazar; G. Lopez; P. Castaño; J. Bilbao (pp. 224-231).

Display Omitted▶ Deactivation of zeolite catalysts of different shape selectivity in HDPE cracking. ▶ Role of zeolite shape selectivity on coke deposition. ▶ Analysis and morphology of the coke deposited on different zeolites. ▶ Good performance of the HZSM-5 zeolite for light olefin production. ▶ Low deactivation by coke with TOS of the HZSM-5 zeolite in the cracking of HDPE.The deactivation of three different catalysts used in the cracking of high density polyethylene (HDPE) has been compared. The catalysts used are HZSM-5, Hβ and HY zeolites agglomerated with bentonite and alumina. The reactions have been carried out in a conical spouted bed reactor at 500°C, and plastic (high density polyethylene) has been fed in continuous mode (1gmin⁻¹) for up to 15h of reaction. The HZSM-5 zeolite catalyst gives way to high yields of C₂–C₄ olefins (57wt%) and, moreover, it is the one least influenced by deactivation throughout the run, which is explained by the lower deterioration of its physical properties and acidity. The results of temperature program combustion and transmission electron microscopy show that coke growth is hindered in the HZSM-5 zeolite pore structure. The high N₂ flow rate used in the conical spouted bed reactor enhances coke precursor circulation towards the outside of the zeolite crystal channels.

Keywords: Coke; Catalyst deactivation; Polyolefins; Recycling; Pyrolysis; Zeolites; Spouted bed reactor

Ruthenium catalyst on carbon nanofiber support layers for use in silicon-based structured microreactors, Part I: Preparation and characterization by D.B. Thakur; R.M. Tiggelaar; T.M.C. Hoang; J.G.E. Gardeniers; L. Lefferts; K. Seshan (pp. 232-242).

Display Omitted▶ Preparation of open-structured catalytic layers in microreactor channels is achieved. ▶ Anchoring Ruthenium on the carbon nanofiber (CNF) surface via homogeneous deposition precipitation and pulsed laser deposition is accomplished. ▶ Deposition by precipitation gives sharp particle size distribution all over CNF layer. ▶ Pulsed laser deposition provide possibility to deposit higher ruthenium loadings. ▶ Array of pillars with optimized spacing help to fill microchannels with CNF layers.The preparation and characterization of ruthenium catalytic nanoparticles on carbon nanofiber (CNF) support layers via homogeneous deposition precipitation (HDP) and pulsed laser deposition (PLD) is presented. Prior to ruthenium deposition the CNF layers were functionalized via liquid phase oxidation treatment using nitric acid at 90°C. This acid treatment not only effectively removed accessible CNF-growth catalyst, but also resulted in the formation of oxygen containing functional groups on the external surface of CNFs. A variety of characterization techniques, viz. TEM, XRD, XRF, XPS, and point-of-zero-charge (PZC) measurements were used to analyze the influence of the oxidation pretreatment on physico-chemical properties of CNF layers qualitatively and quantitatively. HDP yielded a very sharp size distribution (∼85% of the particles had a diameter of 1.0–1.5nm), whereas PLD had a less narrow distribution (the diameter of ∼75% of the particles was 1–3nm). Both methods yielded a ruthenium loading of 2.3±0.1wt.%, and in particular HDP showed uniform anchoring of particles throughout the thickness of the CNF layer. Using optimal conditions, the space in a silicon-based microreactor channel was efficiently filled with open, entangled CNF layer, which were used as anchor points for Ru using HDP and PLD.

Keywords: Carbon nanofibers; Silicon substrates; Homogeneous deposition precipitation; Pulsed laser deposition; Silicon microreactors

Ruthenium catalyst on carbon nanofiber support layers for use in silicon-based structured microreactors. Part II: Catalytic reduction of bromate contaminants in aqueous phase by D.B. Thakur; R.M. Tiggelaar; Y. Weber; J.G.E. Gardeniers; L. Lefferts; K. Seshan (pp. 243-250).

Display Omitted▶ Catalytic microreactor system is used efficiently to remove bromate ions from water. ▶ Carbon nanofiber (CNF) supported ruthenium (Ru) catalyst reduced bromate ions efficiently. ▶ Open structure of CNF provides better accessibility to Ru active sites than in case of microporous activated carbon. ▶ Formation of inactive Ru(OH)_x phase and sintering cause catalyst deactivation. ▶ Use of higher alcohols give stabler activity of Ru/CNF catalyst in bromate reduction.Catalyst layers were synthesized inside a structured channel of silicon based microreactor and used to remove bromate contaminants in water. It is demonstrated that Ru/CNF based catalyst is active for bromate reduction, resulting in turn over frequencies (TOFs) higher than conventional powdered catalyst, i.e. activated carbon (AC). This enhanced catalytic performance can be attributed to improve mass transfer properties of entangled CNF layers with macroporous (open) structure, which offer enhanced accessibility to all the Ru active sites in contrast to the poor accessibility of active sites in the case of AC support material.Although promising catalytic activity of Ru/CNF catalyst was observed for bromate reduction, a continuing deactivation was observed during 5h time on stream operation. A variety of characterization techniques including TEM, XPS, TPR, ICP probed that in addition to catalyst sintering, formation of catalytically inactive Ru(OH)_x phase on catalyst surface was an important reason of this deactivation. Use of higher alcohols proved to be beneficial for achieving stability of Ru/CNF catalyst for bromate reduction, however with reduced levels of overall activity.

Keywords: Carbon nanofibers; Silicon microreactors; Bromate reduction; Redox catalysis

Hydrogen production from steam reforming of ethanol with nano-Ni/SiO₂ catalysts prepared at different Ni to citric acid ratios using a sol–gel method by Chunfei Wu; Paul T. Williams (pp. 251-259).

Display Omitted▶ Nano-Ni/SiO₂ catalysts were prepared using the sol–gel method. ▶ Larger pore volume were obtained when the catalyst was prepared at higher CA content. ▶ Hydrogen production was increased with the catalyst prepared at higher CA content. ▶ Non-stable catalyst was prepared at Ni:CA ratio of 1:0.5 during the ethanol steam reforming.Steam reforming of ethanol to produce hydrogen was carried out using a two-stage reaction system with several nano-Ni/SiO₂ catalysts prepared at different citric acid (CA) contents using the sol–gel process. The fresh (non-calcined and calcined) catalysts and the reacted catalysts were analysed using surface area and pore size analysis, Fourier-transform infrared (FTIR) spectroscopy, thermo-gravimetry analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that a meso-structured material was produced at Ni:CA ratios lower than 1:0.5; and the pore volume of the catalyst was increased when more citric acid was used during the sol–gel preparation. Gas and hydrogen yield were observed to be increased when the Ni:CA ratio was reduced from 1:0.5 to 1:3.0; however, gas concentration was slightly changed for the catalysts prepared at different Ni:CA ratios. In addition, coke formation was increased from 0.7 to 7.5wt.% when the Ni:CA ratio decreased from 1:0.5 to 1:3.0. It was also found that the Ni/SiO₂ catalyst prepared at the low CA content (Ni:CA=0.5) was non-stable during the ethanol steam reforming process; since sintering was obtained as observed using TEM analysis of the used catalyst.

Keywords: Ethanol; Nickel; Hydrogen; Catalyst; Sol–gel

Soot combustion manganese catalysts prepared by thermal decomposition of KMnO₄ by M.E. Becerra; N.P. Arias; O.H. Giraldo; F.E. López Suárez; M.J. Illán Gómez; A. Bueno López (pp. 260-266).

Display Omitted▶ Cryptomelane and/or birnessite can be prepared by thermal decomposition of KMnO₄. ▶ The resulting materials seem promising catalysts for soot combustion in DPF filters. ▶ The catalytic combustion of soot occurs by the NO₂-assisted mechanism.Manganese oxides with cryptomelane and/or birnessite structure have been successfully prepared by thermal decomposition of potassium permanganate. The samples have been characterized by XRD, FTIR, TGA, N₂ adsortion at −196°C, H₂-TPR and XPS, and have been evaluated as catalysts for soot combustion in a NO_x/O₂ gas mixture. KMnO₄ decomposition at 400°C yields birnessite and potassium manganate, and the latter can be removed by water washing. Further calcination at 600°C of the washed birnessite leads to the increase of the birnessite crystallinity and to the partial transformation into cryptomelane. For the unwashed sample, the catalytic effect of potassium, which forms low melting temperature compounds upon NO_x chemisorption, controls the catalytic combustion of soot in a NO_x/O₂ gas mixture. On the contrary, the combustion of soot assisted by these birnessite and cryptomelane catalysts (once manganese salts have been removed) occurs by the NO₂ mechanism, and these catalysts seem promising candidates for practical application in the regeneration of DPF filters.

Keywords: Nanostructured materials; Manganese oxides; Cryptomelane; Birnessite; Solid-state synthesis; Soot combustion

Conversion of poisonous methanethiol to hydrogen-rich gas by chemisorption/reforming over nano-scale CeO₂: The use of CeO₂ as catalyst coating material by N. Laosiripojana; S. Assabumrungrat (pp. 267-275).

Display Omitted▶ Steam reforming of CH₃SH over CeO₂ generates H₂-rich gas (H₂, CO and CO₂). ▶ With sufficient inlet steam content, CeO₂ phase turns to Ce(SO₄)₂ during reaction. ▶ Ce(SO₄)₂ has high OSC, high lattice oxygen mobility and good reforming activity. ▶ Without (or with low steam content), CeO₂ phase turns to Ce₂O₂S during reaction. ▶ Ce₂O₂S has low OSC, low lattice oxygen mobility and poor reforming activity.Synthesized nano-scale CeO₂ enables to convert poisonous methanethiol (CH₃SH) to hydrogen-rich gas via the solid–gas reaction between CeO₂ and CH₃SH under sufficient condition. In the presence of H₂O, the phase of Ce(SO₄)₂ occurs from the reaction and offers high CH₃SH reforming activity. In contrast, without H₂O adding, Ce₂O₂S is formed instead and results in low catalyst activity. Further catalyst improvement was performed by coating this synthesized nano-scale CeO₂ over cylindrical-shape Rh/Al₂O₃ pellet (as called CeO₂-coated Rh/Al₂O₃). This developed catalyst was found to enhance good activity, stability, and reusability (over 5 reaction cycles; 72h) for converting CH₃SH to hydrogen-rich gas with high hydrogen yield achievement. For more practical application, this catalyst was also tested over olefin offgas containing CH₃SH and ethanethiol (CH₃SCH₃) from an olefin manufacturing; and was found to efficiently convert this offgas to hydrogen-rich gas without sulfur present in the product gas under a proper regeneration time. This result highlights a great benefit of CeO₂-coated Rh/Al₂O₃ for integrating the clean energy generation with toxic-waste treatment, which offers significant energy and environmental benefits.

Keywords: CeO; ₂; Steam reforming; Methanethiol; Hydrogen

Highly efficient photocatalytic elimination of phenol and chlorinated phenols by CeO₂/MgAl layered double hydroxides by Jaime S. Valente; Francisco Tzompantzi; Julia Prince (pp. 276-285).

Display Omitted▶ For the first time, CeO₂/MgAl LDHs are used simple and effective photocatalysts. ▶ Capable of degrading twice as much phenol as benchmark Degussa P25 TiO₂. ▶ Very effective in the degradation of 4-chlorophenol and 2,4,6-trichlorophenol. ▶ Degradation may proceed by two different mechanisms. ▶ Charge-transfer mechanism is thought to occur via interaction with basic sites.Mg/Al layered double hydroxides (LDHs) were synthesized by a simple, environment friendly method; then, cerium oxide was incorporated following two different procedures. Thus obtained bifunctional basic/semiconducting catalysts were characterized by several techniques, such as XRD, SEM/EDS, chemical analysis and N₂ physisorption, to investigate their crystalline structure, morphology, CeO₂ content and textural properties. The band gap energy was determined to be ∼3.2eV. The photocatalytic properties of the Ce–Mg–Al system were tested for the first time for the degradation, under UV irradiation, of three major pollutants: phenol, 4-chlorophenol and 2,4,6-trichlorophenol. The results obtained with phenol, which is the most recalcitrant of the studied molecules, were by far superior to those obtained with benchmark Degussa P25 TiO₂ photocatalyst tested under the same conditions. Furthermore, a charge-transfer mechanism is proposed as the initiator of the photocatalytic degradation of phenol and 4-chlorophenol.

Keywords: Photocatalysis; Chlorinated phenols; Cerium oxide; Layered double hydroxides; Charge-transfer mechanism

Visible light photocatalytic activity induced by the carboxyl group chemically bonded on the surface of SrTiO₃ by Uyi Sulaeman; Shu Yin; Tsugio Sato (pp. 286-290).

.Display Omitted▶ The nanoparticles of perovskite type SrTiO₃ (15–18nm) could be synthesized. ▶ Carboxyl (–COO⁻) group of oleic acid chemically bonded in the surface of catalyst. ▶ The visible light photocatalytic of SrTiO₃–oleic acid could be generated.Strontium titanate nanoparticles were synthesized by a microwave-assisted solvothermal reaction of SrCl₂·6H₂O, Ti(OC₃H₇)₄ in KOH methanol–oleic acid solution. The products were characterized by TG-DTA, XRD, TEM, BET surface area and XPS. The photocatalytic activity was determined by DeNO_x ability using LED lamps with various wavelengths such as 627nm (red), 530nm (green), 445nm (blue) and 390nm (UV). The nanoparticles of perovskite type SrTiO₃ with the particle size of 15–18nm were successfully synthesized. The photocatalytic activity of SrTiO₃ under visible light ( λ=530nm) irradiation could be generated by modification of the surface with the carboxyl group (–COO) from oleic acid which enabled the absorption of visible light.

Keywords: Carboxyl; SrTiO; ₃; Nb doping; Visible light; Dipole layer; Photocatalyst

Surface reactivity of LaCoO₃ and Ru/LaCoO₃ towards CO, CO₂ and C₃H₈: Effect of H₂ and O₂ pretreatments by M. Consuelo Álvarez-Galván; Domna A. Constantinou; Rufino M. Navarro; José A. Villoria; José Luis G. Fierro; Angelos M. Efstathiou (pp. 291-301).

Display Omitted▶ Ru promotes “carbon” suppression in propane TPSR on Ru/LaCoO₃. ▶ Ru promotes syngas production during OSR of propane on Ru/LaCoO₃ by enhancing the presence of Co⁰. ▶ Ru reduces the strength of basic sites in Ru/LaCoO₃ compared to LaCoO₃. ▶ Hydrogen compared to oxygen pretreatment of LaCoO₃ or Ru/LaCoO₃ enhances CO₂ chemisortion and “carbon” deposits.The differences in surface reactivity of LaCoO₃ and Ru/LaCoO₃ solids after pre-treatment in a hydrogen or oxygen gas atmosphere towards oxidative steam reforming (OSR) of propane was probed by performing temperature-programmed desorption (TPD) of CO and CO₂, temperature-programmed surface reaction (TPSR) of C₃H₈, transient isothermal oxidation of “carbon” formed after TPSR of C₃H₈, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) studies. The TPD of CO and CO₂ studies revealed a greater adsorption of these molecular product species of the OSR of propane on the surface of LaCoO₃ than Ru/LaCoO₃ solid, while XPS studies performed after reduction in hydrogen revealed a higher concentration of Co²⁺ in the LaCoO₃ than Ru/LaCoO₃ solid catalyst composition. The Ru/LaCoO₃ solid was found to exhibit after an induction period enhanced reactivity towards H₂ production for the OSR of propane reaction compared to LaCoO₃ after hydrogen reduction at 750°C. These results led to the conclusion that the introduction of a small amount of Ru (0.8wt%) on lanthanum cobaltite surface leads to a higher concentration of metallic cobalt (Co⁰) after hydrogen reduction is performed, thus favouring the enhancement of necessary active catalytic sites on the Co, LaCoO₃ and La₂O₃ surfaces formed. TPSR of propane used as model compound of diesel revealed the participation of surface lattice oxygen of both LaCoO₃ and Ru/LaCoO₃ pre-oxidized solids as well as the formation of hydrogen by reaction of propane on the Co⁰ (metallic state) surface once the latter is formed. A greater reactivity of propane during TPSR was observed over the Ru/LaCoO₃ solid surface for either oxidative or reductive pre-treatments. Also, a lower amount (2.13mmol/g) of “carbon” deposition was found on Ru/LaCoO₃ compared to LaCoO₃ (3.65mmol/g) at the end of the TPSR of propane experiment. These results provide important fundamental information on the role of Ru in the Ru/LaCoO₃ system towards catalytic oxidative steam reforming of propane.

Keywords: Oxidative steam reforming of propane; H; ₂; production; LaCoO; ₃; Ru; Perovskite; CO-TPD; CO; ₂; -TPD; Propane TPSR

NO_x reduction performance of fresh and aged Fe-zeolites prepared by CVD: Effects of zeolite structure and Si/Al₂ ratio by Masaoki Iwasaki; Kiyoshi Yamazaki; Hirofumi Shinjoh (pp. 302-309).

Display Omitted▶ SCR activity decreased when Si/Al₂ ratio increased. ▶ SCR activity order of fresh Fe/zeolites was BEA>MFI>FER>LTL>MOR. ▶ SCR activity of fresh states was correlated with HT peak in NO₂-TPD and NO oxidation. ▶ SCR order of 700°C hydrothermally aged samples was MFI>BEA>FER>LTL>MOR. ▶ Deterioration rate of NO_x conversion was correlated with zeolite crystal size.A series of Fe/zeolites with different pore structures (MFI, BEA, FER, LTL, MOR) and Si/Al₂ ratios (6–240) were prepared by chemical vapor deposition (CVD). The activities for selective catalytic reduction by ammonia (NH₃-SCR) of fresh and hydrothermally aged (700°C) samples were measured in order to determine the effect of zeolite species on reactivity and hydrothermal stability. SCR activity decreased with increasing Si/Al₂ ratios for MFI (Si/Al₂=40, 73 and 90) and MOR (Si/Al₂=20, 30 and 240) samples. The SCR activity of fresh samples was dependent on the type of zeolite used as follows: BEA>MFI>FER>LTL>MOR. The order could not be explained by the amount of Fe loading or by specific surface area (SSA), although activity was well correlated with the higher temperature (HT) peak in temperature-programmed desorption (TPD) spectra of NO₂ and with NO oxidation conversion under NH₃-free conditions. The HT peak indicates the number of active Fe sites. Therefore, the major factor affecting SCR activity is the amount of active Fe available to catalyze the oxidation of NO. After hydrothermal aging, the activity of all samples decreased and the order of activity by zeolite type was: MFI>BEA>FER>LTL>MOR. Activity retention ratios estimated from conversions for fresh and aged samples were independent of the number of acid sites and SSA. In contrast, the retention ratios were correlated with the crystal size of the parent H-zeolites.

Keywords: SCR; Fe; Zeolite; Nitrogen oxide; Ammonia

High performance heterogeneous catalyst for biodiesel production from vegetal and waste oil at low temperature by M.E. Borges; L. Díaz; M.C. Alvarez-Galván; A. Brito (pp. 310-315).

Display Omitted▶ Heterogeneous catalytic elimination of environmental pollutants (waste oil) especially applied to biodiesel industrial processes. ▶ Preparation, characterization, activation, deactivation and regeneration of a novel and commercially applicable environmental heterogeneous catalyst. ▶ Production of biodiesel from clean energy (biomass). ▶ Catalytic reaction in which wastes are converted to useful products. ▶ Environmentally friendly biodisel is produced by this catalyst.A natural porous silica, pumice, was studied as heterogeneous catalyst in the transesterification reaction of sunflower oil and frying oil with methanol for biodiesel production. This low cost natural porous material was subjected to ion exchange with a KOH aqueous solution in order to increase its activity. The dependence of the reaction variables such as temperature, reaction time, catalyst loading and methanol/oil molar ratio were studied using sunflower oil and waste oil as feedstock. Moreover, in order to save production costs, the reusability of the catalyst in the transesterification reaction was studied.

Keywords: Biodiesel; Heterogeneous catalyst; Transesterification reaction; Pumice

Study on visible light photocatalytic activity and mechanism of spherical Bi₁₂TiO₂₀ nanoparticles prepared by low-power hydrothermal method by Xiangqi Zhu; Jinlong Zhang; Feng Chen (pp. 316-322).

Display Omitted▶ Synthesiaing Bi₁₂TiO₂₀ nanoparticles within 2h hydrothermal treatment. ▶ Bi₁₂TiO₂₀ has spherical structures with good dispersion and high BET surface area. ▶ Bi₁₂TiO₂₀ has a high activity under visible light irradiation. ▶ The photocatalytic mechanisms were identified.Bismuth titanate (Bi₁₂TiO₂₀) nanoparticles with spherical structures and good dispersion were synthesized hydrothermally using C₆H₁₃BiN₂O₇·H₂O and TiCl₃ in the presence of polyethylene glycol (PEG). Only 2h of hydrothermal process was needed which means the whole process of preparation was a less power consumption. X-ray diffraction (XRD) proved that the samples were in pure cubic phase. UV–vis diffuse reflection spectra showed the band gap of Bi₁₂TiO₂₀ is about 2.65eV. Brunauer–Emmett–Teller (BET) analysis showed that the Bi₁₂TiO₂₀ samples have higher surface areas. Visible-light-induced photodegradation of acid orange 7 (AO7) on Bi₁₂TiO₂₀ was investigated. It was found that Bi₁₂TiO₂₀-assisted photocatalytic degradation of AO7 occurs via two processes: the photocatalytic process of Bi₁₂TiO₂₀ semiconductor and the photosensitized process of AO7. Photocatalytic experiments in the presence of N₂ and the radical scavenger suggested thatOH and O₂⁻ are two main active species in the whole degradation process.

Keywords: Bi; ₁₂; TiO; ₂₀; nanoparticles; Ammonium Bismuth Citrate; Acid orange 7; Photocatalytic degradation; Active species

The role of silver nanoparticles on silver modified titanosilicate ETS-10 in visible light photocatalysis by Zhaoxia Ji; Mariam N. Ismail; Dennis M. Callahan Jr.; Eko Pandowo; Zhuhua Cai; Trevor L. Goodrich; Katherine S. Ziemer; Juliusz Warzywoda; Albert Sacco Jr. (pp. 323-333).

Display Omitted▶ Ag participates in e-transfer from photoexcited MB to O₂ adsorbed on the Ag. ▶ ETS-10 is mainly inactive but provides a reservoir for MB during photocatalysis. ▶ Ag nanoparticles on ETS-10 surfaces dislodge into solution during photocatalysis.Nanoparticles of noble metals, such as silver and gold, have been investigated as one way to hinder the recombination of electrons and holes produced by irradiated semiconductors. However, the exact role silver plays in hindering electron–hole recombination is unclear. In order to assess the role of ionic silver, Ag⁺, and metallic silver, Ag⁰, on the potential photocatalytic activity of a titanosilicate ETS-10 semiconductor (i.e., a means to extend light absorption into the visible range, a means to form a Schottky barrier to hinder electron–hole recombination, as a catalyst for the production of oxygen radicals, as a means to capture electron through species reduction, etc.) the photosensitization of methylene blue (MB) was investigated under visible light irradiation. Visible light irradiation was chosen so as to decouple the effects silver nanoparticles play in this photosensitized reaction from the complexities of electron–hole pair dynamics that may be inherent to ETS-10. Ag⁺ and Ag⁰ were investigated in both their free-floating forms and utilizing ETS-10 as a substrate. All forms of silver were produced by AgNO₃ dissociation. Ion exchange of as-synthesized ETS-10 from AgNO₃ solutions was utilized to prepare Ag⁺-modified ETS-10 (Ag⁺–ETS-10), and H₂ reduction of Ag⁺–ETS-10 was used to prepare Ag⁰ nanoparticle-modified ETS-10 (Ag⁰–ETS-10). In all preparations, the morphology and crystal structure of ETS-10 remained unchanged. Ag⁺–ETS-10 samples showed a progressive absorption edge red shift in the UV region with increasing sample Ag⁺ content. Unlike as-synthesized ETS-10 and Ag⁺–ETS-10 samples, Ag⁰–ETS-10 samples showed absorbance in the visible region. The absorption bands at ∼350nm and ∼460nm observed for Ag⁰–ETS-10 were attributed to the surface plasmon resonance of Ag⁰ nanoparticles on the surface of ETS-10 crystals. In contrast to as-synthesized ETS-10, which was essentially inactive in this illumination range, all Ag⁺–ETS-10 and Ag⁰–ETS-10 samples showed apparent enhanced activity for the degradation of MB under visible light (420–630nm) irradiation. These results suggest that silver nanoparticles provide a “portal” for oxygen (i.e., oxygen radicals) to interact with MB radicals by providing a medium for interfacial charge transfer of an electron to oxygen adsorbed on the silver, with ETS-10 providing a reservoir for MB molecules and their radicals, and a path for injected electrons to reduce Ag⁺.

Keywords: ETS-10; Methylene blue; Photocatalysis; Silver nanoparticles; Titanosilicates

Effect of PtRu alloying degree on electrocatalytic activities and stabilities by Kug-Seung Lee; Tae-Yeol Jeon; Sung Jong Yoo; In-Su Park; Yong-Hun Cho; Soon Hyung Kang; Kwang Hyun Choi; Yung-Eun Sung (pp. 334-342).

Display Omitted▶ PtRu alloying degree was controlled using various water contents in a solvent. ▶The PtRu alloying degree was changed approximately from 18% to 86%. ▶ Methanol oxidation activity was improved on highly alloyed catalysts. ▶ Stability for methanol oxidation was higher on highly alloyed catalysts.The PtRu alloying degree was controlled by mixing various amounts of water in the solvent while the nominal Pt/Ru ratio was remained at the value of one, and the relationship between the alloying degree and electrochemical activities was examined in this study. X-ray diffraction analysis showed that the fraction of the alloyed Ru ranged from approximately 18% for 100% water solvent to 86% for 0% water solvent. In X-ray photoelectron spectroscopy (XPS), Pt and Ru metallic components increased with the PtRu alloying degree. Electrochemical activities for CO oxidation and methanol oxidation were enhanced as the PtRu alloying degree became higher. Electrochemical stability was also investigated via potential cycling in a methanol-contained electrolyte solution. After the potential cycling process, the catalysts were analyzed by transmission electron microscopy, XPS, XPS element mapping. Possible reasons for the difference in the electrochemical stability of the catalysts were discussed.

Keywords: Electrochemical stability; Alloying degree; Direct methanol fuel cell; XPS element mapping; Bifunctional mechanism

Green fabrication of La-doped NaTaO₃ via H₂O₂ assisted sol–gel route for photocatalytic hydrogen production by Husni Husin; Hung-Ming Chen; Wei-Nien Su; Chun-Jern Pan; Wei-Tsung Chuang; Hwo-Shuenn Sheu; Bing-Joe Hwang (pp. 343-351).

Display Omitted▶ Nanosized and La doped NaTaO₃ photocatalyst with high crystallinity can be successfully produced. ▶ These features of La-doped NaTaO₃ facilitate charge separation and suppress the recombination. ▶ H₂O₂ helps form tantalum-peroxo to reduce the particle growth and the calcinations temperature. ▶ The route allows a lower calcination temperature and gives less organic byproducts. ▶ Crystallography analysis helps explain the effect of doping on the photocatalytic activity.Crystalline NaTaO₃ nanoparticles doped with different concentrations of La³⁺ have been synthesized via a H₂O₂-assisted sol–gel route. In this reaction, TaCl₅ is dissolved in aqueous H₂O₂ solution to form a stable transparent Ta-peroxo complex solution. The formation of tantalum-peroxo complexes and their chelation by citric acid enables a better control of crystal growth. X-ray diffraction and scanning/transmission electron microscopy provide useful information about crystallinity and morphology of the samples. The substitution of La³⁺ ions in the NaTaO₃ lattice is verified by crystallographic simulation (CaRIne Crystallography version 3.1). These results indicate La³⁺ ions occupy the Na⁺ ions sites, which agrees very well with the experimental data. The optimal content of La³⁺ ions effectively increases crystallinity without agglomeration, contributing to efficient charge separation and preventing recombination between photogenerated electrons and holes. The highest photocatalytic H₂ production of 1.43mmolh⁻¹ is obtained for a 2.0mol% La-doped NaTaO₃ sample. The NaTaO₃ nanoparticles produced using this facile, environmentally friendly ‘green process’ have better crystallinity, smaller size and higher photocatalytic activity.

Keywords: La-doped sodium tantalum oxide; Photocatalyst; Nanoparticle; Tantalum-peroxo complex; Hydrogen evolution

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Applied Catalysis B, Environmental (v.102, #1-2)