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Applied Catalysis B, Environmental (v.95, #3-4)

Contents (pp. iii).

Contents (pp. co4).

Editorial Board (pp. co2).

Editorial Board (pp. i).

Mn^II—A fascinating oxidation catalyst: Mechanistic insight into the catalyzed oxidative degradation of organic dyes by H₂O₂ by Erika Ember; Hanaa Asaad Gazzaz; Sabine Rothbart; Ralph Puchta; Rudi van Eldik (pp. 179-191).

The use of simple Mn^II ions as efficient catalyst precursors for the oxidation of various highly stable organic dyes using H₂O₂ as an environmentally benign oxidant under mild reaction conditions, is presented. The role of a series of aromatic dyes in the in situ formation and stabilisation of the active catalyst was studied in detail using stopped-flow techniques and UV–Vis detection.The use of simple Mn^II ions as efficient catalyst precursors for the oxidation of different highly stable organic dyes using H₂O₂ as an environmentally benign oxidant under mild reaction conditions, is presented. The role of a series of aromatic dyes in the in situ formation and stabilisation of the active catalyst was studied in detail using stopped-flow techniques and UV–Vis detection. DFT calculations were employed to predict the nature of the role of the substrate in the stabilisation of highly reactive Mn^II intermediates. Furthermore, low-temperature EPR measurements were performed in order to characterize the in situ formed catalytically active Mn^IVO intermediate responsible for the fast and versatile oxidation of organic dyes in aqueous solution.

Keywords: Green catalysis; Manganese salts; Activation of H; ₂; O; ₂; Oxidative degradation; Organic dyes

Microwave-activated direct synthesis of acrylonitrile from glycerol under mild conditions: Effect of niobium as dopant of the V-Sb oxide catalytic system by Vanesa Calvino-Casilda; M. Olga Guerrero-Pérez; Miguel A. Bañares (pp. 192-196).

Glycerol is a major by-product in biodiesel production, which raises a critical need to develop efficient valorization processes. This study shows how both conventional thermal activation and microwave irradiation are able to selectively transform glycerol into acrylonitrile, this performance is modulated by niobium doping of Sb_nV/Al₂O₃ catalysts under mild reaction conditions. To the best of our knowledge, we report the highest selectivity (83.8%) to acrylonitrile from glycerol at good conversion values (46.8%).

Keywords: Glycerol; Acrylonitrile; Biomass; Microwave activation; Catalytic process; Sustainability

Synchronous role of coupled adsorption and photocatalytic oxidation on ordered mesoporous anatase TiO₂–SiO₂ nanocomposites generating excellent degradation activity of RhB dye by Weiyang Dong; Chul Wee Lee; Xinchun Lu; Yaojun Sun; Weiming Hua; Guoshun Zhuang; Shicheng Zhang; Jianmin Chen; Huiqi Hou; Dongyuan Zhao (pp. 197-207).

Synchronous role of coupled adsorption and photocatalytic oxidation on unique 2-D hexagonal mesoporous anatase TiO₂–SiO₂ nanocomposites generates excellent photocatalytic degradation activity of RhB dye.In this paper, we report a synchronous role of coupled adsorption and photocatalytic oxidation on ordered 2-D hexagonal mesoporous TiO₂–SiO₂ nanocomposites with large pore channels (>4.0nm) and high specific surface areas (>70m²g⁻¹). These mesoporous frameworks consist of anatase TiO₂ nanocrystals and amorphous SiO₂ nanomatrixes, which link mutually, coexist to form unique composite-walls, providing unprecedented spaces for “the synchronous role of coupled adsorption and photocatalytic oxidation”. SiO₂ nanomatrixes are excellent adsorbents, providing better adsorption centers and enriching organic pollutant molecules; while anatase nanocrystals behave as photocatalytic active sites to oxide the organic molecules pre-enriched by the surrounding SiO₂ particles. Moreover, the high accessible surface areas can provide more adsorptive and photocatalytically active sites; and the large mesopore channels allow the reactive molecules to diffuse more easily both into and out of the inner surfaces before and after photocatalytic reactions, respectively. Our strategy realizes the synchronous role by adjusting Ti/Si ratios, the number of surface hydroxyls, the size and crystallinity of the anatase nanocrystals on the unique composite-frameworks. The cationic rhodamine-B (RhB) dye is used as the target pollutant to characterize the adsorption performance and photocatalytic activities. Our results show that the synchronous role results in excellent photocatalytic degradation activity ( k=0.231min⁻¹), which is much higher than that of Degussa commercial P25 photocatalyst ( k=0.0671min⁻¹).

Keywords: Synchronous role; Adsorption; Photocatalytic oxidation; Ordered mesoporous anatase TiO; ₂; –SiO; ₂; nanocomposites; RhB dye

Promoting behaviors of alkali compounds in low temperature methanol synthesis over copper-based catalyst by Baoshan Hu; Kaoru Fujimoto (pp. 208-216).

Hybrid catalyst systems comprised of Na compounds (HCOONa, NaOH, Na₂CO₃ and NaHCO₃) and Cu/MgO catalysts have contributed to a novel high-performance methanol synthesis in ethanol solvent from syngas (CO/H₂=1/2) at a low temperature of 433K and 5MPa. It is found that Na₂CO₃ dopant is more beneficial to enhance hydrogenolysis ability of Cu/MgO catalyst than NaOH and HCOONa. Whereas, all the starting Na compounds in ethanol solvent are reversibly converted to HCOONa in alcohol solvent by ex situ observations, revealing that formate alone is the essential species in the catalytic circle. The results unambiguously elucidate that the essence of alkali component in promoting the low temperature methanol synthesis is virtually attributed to the formation of highly reactive alkali-participated active site. It is also proposed that solid Cu/MgO catalyst should play binary roles in successive carbonylation and hydrogenolysis reactions.

Keywords: Methanol synthesis; Low temperature; Sodium compound; Cu/MgO catalyst; Active site

Catalytic oxidation of heavy hydrocarbons over Pt/Al₂O₃. Influence of the structure of the molecule on its reactivity by Fabrice Diehl; Jacques Barbier Jr.; Daniel Duprez; Isabelle Guibard; Gil Mabilon (pp. 217-227).

Deep oxidation of 48 hydrocarbons (HCs), from 6 to 20 carbon atoms, was studied over a 1%Pt/Al₂O₃ catalyst (105m²g⁻¹; mean particle size of Pt: 1nm). The oxidation reaction (1500ppm C of HC in air) was carried out by increasing the temperature by step of 5°C from 100 to 400°C. The reactivity of HCs was characterized by their T₅₀ (temperature at 50% conversion). The reactivity of n-alkanes increases with the chain length, following the same evolution with n as the ionization potential of the molecule. Isoalkanes are more difficult to oxidize than the corresponding n-alkanes. Hydrocarbon reactivity depends on the nature of carbon in the molecule. The ability to be oxidized is greater with C_II and C_III carbons while C_I and C_IV carbons, still more than C_I, are refractory to oxidation. The reactivity of n-alkenes depends relatively little on the number of carbons in the molecule. Light alkenes are much more reactive than light alkanes while the reverse can be observed with long-chain hydrocarbons. Contrary to branched alkanes, isoalkenes or cyclenic hydrocarbons are generally more reactive than the corresponding n-alkenes. Short side-chain alkylbenzenes (toluene, ethylbenzene, …) and polymethylbenzenes are more difficult to oxidize than benzene. When the length of the alkyl group is increased, the behaviour of the hydrocarbon in oxidation resembles more and more to long-chain alkanes with a better oxidability. Polyalkylbenzenes with hindered heavy alkyl groups are quite easy to oxidize. The behaviour of bicyclic or tricyclic hydrocarbons is much more complex. Partial or complete hydrogenation increases their reactivity. For instance, oxidability of bicyclic hydrocarbons is in the order: decaline>tetraline>naphthalene. The reactivity of heavier aromatics also depends on their ability to form partial oxidation intermediates (for instance: fluorene to fluorenone) or to possess extremely rigid internal CC bonds (for instance: acenaphthylene and acenaphthene). These results were discussed in the light of several factors which can affect the reactivity in oxidation: (i) an electron transfer between adsorbed hydrocarbon and adsorbed oxygen species via the surface metal atoms; (ii) the mean C–H bond strength in the molecule and hindrance effects in branched hydrocarbons; (iii) the relative adsorption strength of oxygen and hydrocarbons; (iv) the relative reactivity of hydrocarbons and partially oxidized molecules, intermediates in total oxidation.

Keywords: Hydrocarbon catalytic oxidation; Pt catalysts; Light-off temperatures; Diesel heavy hydrocarbons; Polycyclic aromatic hydrocarbons (PAHs); Structural effects of hydrocarbon molecules

Efficiency of different solar advanced oxidation processes on the oxidation of bisphenol A in water by Eva M. Rodríguez; Guadalupe Fernández; Nikolaus Klamerth; M. Ignacio Maldonado; Pedro M. Álvarez; Sixto Malato (pp. 228-237).

The efficiencies of different solar oxidation processes on the degradation of bisphenol A in water were studied. The work focuses on the removal and mineralization of bisphenol A and the formation of phenolic intermediates.The processes tested were Fe(III) photolysis, ferricarboxylate photolysis, TiO₂ photocatalysis, H₂O₂ photolysis and combinations thereof. The influence of pH and the presence of hematite (α-Fe₂O₃) on their efficiency, as well as the nature of intermediates formed and development of toxicity were evaluated.

Keywords: Bisphenol A; Solar AOPs; Solar CPC pilot plant; Phenolic intermediates; Toxicity

N- and/or W-(co)doped TiO₂-anatase catalysts: Effect of the calcination treatment on photoactivity by Anna Kubacka; Gerardo Colón; Marcos Fernández-García (pp. 238-244).

A series of nanosized W,N-codoped and single-doped N- and W-anatase-TiO₂ catalysts have been prepared by a microemulsion method and calcined at different temperatures. The activity in the sunlight selective photo-oxidation of toluene and styrene has been correlated with structural, electronic, and surface examinations of the catalysts done with the help of XRD-Rietveld, N₂ physisorption, X-ray photoelectron, infrared, electron paramagnetic resonance (EPR) and UV–vis spectroscopies. Irrespective of the reaction, W,N-codoped nanocatalysts showed an enhanced photoactivity with respect to bare anatase and single-doped N-TiO₂ and W-TiO₂ materials. A strong W–N synergistic interaction appears to play a decisive role in driving the excellent photoactivity performance of W,N-codoped materials by affecting (i) electronic properties, particularly maximizing the anatase band gap decrease and enhancing the subsequent visible light photon absorption, and (ii) surface properties, in turn related to the formation of OH radicals upon light excitation. The maximum photoactivity is reached by calcination at 450°C and is concomitantly observed with a near complete selectivity to partial oxidation products. Higher calcination temperatures yielded solids with significantly inferior photocatalytic performance. The properties of the W–N interaction are discussed as a function of the calcination temperature.

Keywords: Photocatalysis; Titania; Doping; Nitrogen; Tungsten; Nanostructured mixed oxide; Visible and sunlight absorption; Selective partial oxidation; Toluene; Styrene

NO_x photocatalytic degradation employing concrete pavement containing titanium dioxide by M.M. Ballari; M. Hunger; G. Hüsken; H.J.H. Brouwers (pp. 245-254).

In the present work the degradation of nitrogen oxides (NO_x) by concrete paving stones containing TiO₂ to be applied in road construction is studied. A kinetic model is proposed to describe the photocatalytic reaction of NO_x (combining the degradation of NO and the appearance and disappearance of NO₂) in a standard laminar flow photoreactor irradiated with UV lamps employing only NO as the contaminant source. In addition, the influences of several parameters that can affect the performance of these stones are investigated, such as NO inlet concentration, reactor height and flow rate. The kinetic parameters present in the NO and NO₂ reaction rate are estimated employing experimental data obtained in the photoreactor. The obtained model predictions employing the determined kinetic constants are in good agreement with the experimental results of NO and NO₂ concentration at the reactor outlet.

Keywords: Heterogeneous photocatalysis; Nitrogen oxides; Air purification; Concrete roads; NO and NO; ₂; kinetic model

A comparative study of the steam reforming of phenol towards H₂ production over natural calcite, dolomite and olivine materials by Domna A. Constantinou; José Luis G. Fierro; Angelos M. Efstathiou (pp. 255-269).

Pre-calcined (air, 850°C) naturally occurring calcite, dolomite and olivine materials were studied for phenol steam reforming towards H₂ production. The effect of reaction temperature, feed volume flow rate, and hydrogen concentration in the feed stream on phenol conversion, H₂ product concentration and selectivity were investigated. The increase of reaction temperature in the 650–800°C range led to the increase of phenol conversion and H₂-selectivity for the calcite and dolomite materials, while the opposite behaviour was observed for the olivine material. An increase of phenol conversion was obtained with decreasing Gas Hourly Space Velocity, GHSV in the 40,000–80,000h⁻¹ range for all three natural materials studied. The lower activity (per gram basis) of pre-calcined olivine compared to that of pre-calcined calcite and dolomite at high reaction temperatures (750–800°C) is suggested to be linked to the increased extent of reducibility of α-Fe₂O₃ and Fe₃O₄, and of Fe_xMg1−_xO_y and Ca₂Fe₂O₅ phases likely present (X-ray diffraction measurements) in the pre-calcined olivine into less reactive Fe^IIO and Fe⁰ under reaction conditions. X-ray photoelectron spectroscopy studies performed over the raw olivine revealed also the presence of Fe^IIO. Phenol steam reforming reaction followed by transient isothermal oxidation allowed the measurement of “carbonaceous” species that react towards CO and CO₂ and which accumulate during phenol steam reforming, as a function of reaction temperature and time on stream. The lower amount of “carbonaceous” species formed on the surface of calcined olivine under steam reforming of phenol at 650°C, as well as its higher site reactivity compared to calcite and dolomite are considered likely reasons for the higher activity and H₂-yield exhibited by olivine at 650°C compared to calcite and dolomite. Comparative studies regarding the CO₂ adsorption characteristics over pre-calcined calcite, dolomite and olivine using in situ CO₂-DRIFTS and CO₂-TPDs were conducted. It was found that olivine accommodates significantly lower amounts of CO₂ compared to calcite and dolomite. The effect of hydrogen concentration in the feed stream towards phenol steam reforming activity on dolomite was found to be negative. In situ DRIFTS studies using H₂/H₂O/Ar and H₂/H₂O/CO₂/He gas atmospheres suggested that this effect is related to the substantial decrease in the rate of water dissociation to form –OH active species caused by the simultaneous reversible interaction of H₂ with the MgO/CaO surfaces.

Keywords: Phenol steam reforming; Hydrogen production; Natural calcite; Dolomite and olivine; XPS; EDX; HRTEM; Transient experiments; CO; ₂; -TPD; H; ₂; -TPR; CO; ₂; -DRIFTS

Characterization and catalytic activity of CuFeZSM-5 catalysts for oxidative degradation of Rhodamine 6G in aqueous solutions by M. Dükkancı; G. Gündüz; S. Yılmaz; Y.C. Yaman; R.V. Prikhod’ko; I.V. Stolyarova (pp. 270-278).

This study presents an evaluation of the catalytic performances of Fe and Cu containing ZSM-5 zeolites for oxidation of Rhodamine 6G. Fe and Cu were loaded by ion exchange or through hydrothermal synthesis. The catalytic process was carried out in an aqueous solution using H₂O₂ as an oxidant. The catalyst prepared by hydrothermal synthesis showed the highest activity (100% decolorization, 59.1% aromatic degradation and 51.8% TOC removal at initial pH of 3.5). This catalyst was stable against leaching even at low pH. The change in activity of the catalysts prepared was attributed to incorporation of the Fe and Cu species with ZSM-5. Fe and Cu were in structural locations – in the framework – in the catalyst prepared by hydrothermal synthesis while there were extraframework cations or species in catalysts prepared by ion exchange. Incoporation of Cu into FeZSM-5 increased its catalytic activity.

Keywords: CuFeZSM-5 zeolite; Ion exchange; Hydrothermal synthesis; Rhodamine 6G; Hydrogen peroxide

Deactivation of organosulfonic acid functionalized silica catalysts during biodiesel synthesis by A.C. Alba-Rubio; F. Vila; D. Martín Alonso; M. Ojeda; R. Mariscal; M. López Granados (pp. 279-287).

The reusability of silica functionalized with 4-ethyl-benzene sulfonic acid groups used as catalyst in biodiesel production from sunflower oil/methanol mixtures has been investigated. This material was used for four runs under batch mode operation, at different reaction temperatures (373, 423 and 473K), with a catalyst loading of 1.5wt.% referred to oil and with a methanol/oil molar ratio equal to 6. The catalyst is significantly deactivated during the first run, while the activity for the second and successive runs are very similar.Fresh and used catalysts were characterized by chemical analysis, N₂ adsorption–desorption isotherms, infrared spectroscopy and evolved gas analysis by mass spectrometry. Leaching of the organosulfonic groups and adsorption of organic compounds onto the acid sites was detected in the used catalysts. Reactants and products are involved in the leaching process, although glycerine has the highest leaching capacity. The organic deposits are formed by side reactions involving reactants and/or products. The solid porous structure remained unchanged after catalyst use, indicating that sintering or other alterations of the porous network can be discarded as source of deactivation. Leaching and deposition effects occur predominantly during the first run, slowing down notably in subsequent cycles. Both leaching and organic deposits participate of the deactivation; the latter increases its impact at reaction temperatures higher than 423K.Partial catalyst regeneration by removal of the organic adsorbates could not be achieved by treatment at high temperature because the deposits and the organosulfonic acid sites were combusted simultaneously.

Keywords: Biodiesel; Deactivation; Acid catalyst; Leaching; Poisoning; Fouling

Minimization of the deactivation of palladium catalysts in the hydrodechlorination of trichloroethylene in wastewaters by Salvador Ordóñez; Beatriz P. Vivas; Fernando V. Díez (pp. 288-296).

The deactivation of carbon- and alumina-supported palladium catalysts used for trichloroethylene (TCE) hydrodechlorination in wastewaters at mild conditions is studied in this work. TCE concentrations are in the interval of industrial wastewaters (200–900ppm, corresponding to 1.54–6.92mmol/L). Reaction studies have been performed in both batch slurry reactor and continuous fixed bed reactor. In both cases, a deactivation model (considering first-order kinetics for the main reaction, first-order deactivation kinetics, and the residual activity of the deactivated catalyst) has been proposed and experimentally validated. In general terms, carbon-supported catalysts are the most stable. Deactivation behavior can be explained in terms of the aqueous-phase redox and complexation equilibria of the active phase. The effect of different operation approaches, such the modification of the pH or the addition of alkalinity sources has been tested, being observed that the addition of sodium carbonate largely increases the catalyst stability.

Keywords: Pd catalysts; Hydrogenolysis; Deactivation modeling; Aqueous-phase catalytic reactions; Alkalinity effects

Complete dechlorination of pentachlorophenol by a heterogeneous SiO₂–Fe–porphyrin catalyst by Konstantinos C. Christoforidis; Maria Louloudi; Yiannis Deligiannakis (pp. 297-302).

A highly efficient catalyst has been produced by immobilizing a biomimetic iron–porphyrin complex onto SiO₂. The catalyst was found to be highly efficient on the degradation of pentachlorophenol (PCP) achieving 100% of PCP decomposition within 2.5h. Furthermore, complete dechlorination of the initial added PCP substrate was accomplished at the end of the reaction time. Dechlorination proceeded even after PCP was fully decomposed. The initial and main final metabolites of PCP decomposition were identified and a general catalytic mechanism is proposed.

Keywords: Catalysis; Chlorinated compounds; Iron–porphyrin; Ferryl; Dechlorination; LC–MS; Heterogeneous; PCP

Effect of Pt/Pd ratio on catalytic activity and redox behavior of bimetallic Pt–Pd/Al₂O₃ catalysts for CH₄ combustion by Paola Castellazzi; Gianpiero Groppi; Pio Forzatti (pp. 303-311).

In the present work CH₄ combustion activity and reduction/oxidation behavior of bimetallic Pt–Pd/Al₂O₃ catalysts with constant Pd loading (2%, w/w) and different Pt/Pd atomic ratios (0, 0.10, 0.25 and 1) are investigated in the presence of alternated CH₄ lean combustion/CH₄-reducing pulses at 350°C. In the fresh samples, according to XRD and CH₄-TPR measurements, Pd is always totally present as PdO and the CH₄ combustion activity is progressively promoted by Pt addition. On the other hand the reactivity scale is substantially changed (Pt/Pd=0.10≥Pt/Pd=0>Pt/Pd=0.25≫Pt/Pd=1) after a conditioning treatment consisting of several reduction/oxidation cycles in CH₄-containing atmosphere, which has a progressively positive effect on decreasing the Pt content. Indeed, such a treatment results in a 20-fold catalytic activity enhancement for the monometallic sample (Pt/Pd=0), whereas it has different effects on the bimetallic catalysts depending on the Pt/Pd ratio: for Pt/Pd=0.10 the activity markedly increases up to the highest level among the tested catalysts (fresh and conditioned); for Pt/Pd=0.25 the activity is substantially unchanged while for the Pt/Pd=1 it is completely suppressed after the first CH₄-reducing pulse.Such different behavior is mainly related to the influence of Pt on bulk reduction/re-oxidation properties of palladium; TPO data indicate a strong inhibition of Pt on Pd oxidation, which is completely suppressed for the Pt/Pd-1 catalyst, thus explaining the wide loss of activity after reduction for Pt/Pd-1 and confirming that PdO is the most active phase. In the case of the samples with Pt/Pd=0.25 and Pt/Pd=0.10 the inhibiting effect of Pt on Pd oxidation is progressively reduced, resulting in a fraction of PdO formed at the end of the conditioning process equal to 35% and 85% of total Pd, respectively.In line with a Mars van Krevelen redox mechanism controlled by PdO surface reduction by CH₄, for the monometallic sample the activity enhancement upon conditioning is associated with an increase of bulk PdO reducibility, as determined by CH₄-TPR experiments. Such a correlation is not observed in bimetallic samples possibly due to the ability of metallic Pt to activate CH₄ under net reducing conditions (CH₄-TPR), which is suppressed under net oxidizing conditions (lean combustion).

Keywords: Natural gas vehicles; CH; ₄; emissions; Catalytic combustion; Pd catalysts; Bimetallic catalysts

Effect of key parameters on the photocatalytic oxidation of toluene at low concentrations in air under 254+185nm UV irradiation by Natalia Quici; María L. Vera; Hyeok Choi; Gianluca Li Puma; Dionysios D. Dionysiou; Marta I. Litter; Hugo Destaillats (pp. 312-319).

The effect of key experimental parameters on the removal of toluene under 254+185nm irradiation was investigated using a benchtop photocatalytic flow reactor. Toluene was introduced at low concentrations between 10 and 500ppbv, typical of indoor environments, and reacted on TiO₂-coated Raschig rings. Two different TiO₂-coated rings were prepared: in one case, by dip-coating using a P25 aqueous suspension and, on the other, using an organic/inorganic sol–gel method that produced thin films of mesoporous anatase. Flow rates in the photoreactor varied between 4Lmin⁻¹ and 125mLmin⁻¹, leading to residence times in the range 100ms< τ<2s. Toluene removal efficiencies were between 30% and 90%, indicating that the system did not achieve total conversion under the present experimental conditions. For each air flow rate, the conversion of toluene was significantly higher when the reactor length was 10cm, as compared with 5cm; however, only marginal increases in conversions were achieved in the two reactor lengths at equal residence time and different concentrations of toluene, suggesting that the system is effectively behaving as an ideal reactor and that the reaction is first-order in the concentration of toluene. Experiments were carried out between 0% and 66% relative humidity (RH), the fastest reaction rate being observed at moderately low humidity conditions (10% RH). Formaldehyde was formed as a partial oxidation byproduct at low and at high residence times (240 and 960ms), although higher formaldehyde molar yields (up to 20%) were observed at low τ (240ms) and moderate humidity conditions (10% and 33%), suggesting that both τ and RH can be optimized to reduce the formation of harmful intermediates. Toluene removal efficiency increased with the TiO₂ thickness (i.e., mass) until a maximum value of 500nm, beyond which the removal efficiency did not increase further.

Keywords: Heterogeneous photocatalysis; TiO; ₂; Titania; Toluene; UVPCO; Photocatalytic oxidation; Air treatment; Indoors

Improvement in heat resistance of NOx trap catalyst using Ti–Na binary metal oxide as NOx trap material by Hidehiro Iizuka; Masato Kaneeda; Norihiro Shinotsuka; Osamu Kuroda; Kazutoshi Higashiyama; Akira Miyamoto (pp. 320-326).

The purpose of this study was to identify suitable base materials for NOx trap catalysts from the viewpoint of heat resistance. First, suitable elements among alkali metals (M: K, Na, Li) and alkaline earth metals (M: Ba, Ca, Sr, Mg) were evaluated using M–Rh,Pt/Al₂O₃. Na was found to be the most suitable element that combines NOx trap performance with hydrocarbon purification performance after heat treatment at 973K. Moreover, the effects of binary metal oxides with Na and M′ (Zr, Fe, W, Mo, Ti) were evaluated to improve the heat resistance of Na–Rh,Pt/Al₂O₃. The ranking of the NOx trap activity of M′ was Ti>none>Fe>W>Zr>Mo; Ti was the most suitable additional element for improving heat resistance of Na–Rh,Pt/Al₂O₃. The maximum amount of NOx conversion and the maximum number of base sites of Ti,Na–Rh,Pt/Al₂O₃ were reached at a Ti/Na mol ratio of 0.1. It was inferred that the addition of Ti to Na–Rh,Pt/Al₂O₃ formed a Ti–Na binary metal oxide from catalyst characterisation by X-ray diffraction and X-ray photoelectron spectrometry, and this Ti–Na binary metal oxide improved the thermal stability of Na–Rh,Pt/Al₂O₃. Finally, from vehicle tests, it was clear that the NOx trap catalyst, which supported Ti–Na binary metal oxide, exhibited high heat resistance.

Keywords: NOx trap catalyst; Alkali metals; Alkaline earth metals; Na; Ti; Binary metal oxide; Heat resistance

Catalytic performance of pillared interlayered clays (PILCs) supported CrCe catalysts for deep oxidation of nitrogen-containing VOCs by Qinqin Huang; Shufeng Zuo; Renxian Zhou (pp. 327-334).

Na-montmorillonite (Na-mmt) and different pillared interlayered clays (Al-PILC, Zr-PILC, Ti-PILC and Al₂O₃/Ti-PILC) supported CrCe catalysts for the deep oxidation of nitrogen-containing VOCs (NVOCs) are synthesized and characterized by a combination of X-ray diffraction, N₂ adsorption/desorption, high resolution transmission electron microscopy, temperature-programmed reduction, temperature-programmed desorption and adsorption capacity tests techniques. The results indicate that a porous structure named “house of cards” forms during the pillaring and calcination processes. Both porous structure and acidity play important roles in deep oxidation of NVOCs. The mesoporous structure and the proper acid sites improve the catalytic activity of supported CrCe catalysts. Among all these catalysts, CrCe/Ti-PILC and CrCe/Al₂O₃/Ti-PILC exhibit higher catalytic activity than other catalysts. N-butylamine and ethylenediamine with –NH₂ groups are easier to be destructed may be involved in the stronger adsorption on the acid sites of the catalysts. Much too strong adsorption of ethylenediamine on the acid sites leads to a lower activity compared with n-butylamine. Acetonitrile with C≡N bond and little interaction with acid sites is the most difficult to be decomposed. All the catalysts show a good control quality of NO_x, and the yield of NO_x is limited within 2% during the whole experimental temperature range.

Keywords: Pillared interlayered clays; Supported CrCe catalysts; NVOCs oxidation; Porous structure; Acidity

Flame-assisted synthesis of nanoscale, amorphous and crystalline, spherical BiVO₄ with visible-light photocatalytic activity by Nikola C. Castillo; Andre Heel; Thomas Graule; Cesar Pulgarin (pp. 335-347).

The synthesis of bismuth vanadate (BiVO₄) nanoparticles has drawn considerable attention to their application as a visible-light-driven photocatalyst. Several techniques are addressing the enlargement of surface area, but some of them can cause impurities and lower the performance of the material. In this work, flame spray synthesis technique was used as a simple, easy upscalable technique to produce BiVO₄ powders. The effect of process parameters on particle properties such as size, morphology and crystallinity were investigated by several techniques: BET, XRD, DSC, TEM, DRS andζ potential. Spherical BiVO₄ nanoparticles with either amorphous or monoclinic phase-pure crystal structure, along with specific surface areas (SSA) between 10 and 75m²g⁻¹ were obtained by a setup including an in situ crystallization step atT≥ 270°C on the powder collection site, sometimes followed by a mild or severe annealing post-treatment. Traditional synthesis routes usually require such annealing post-treatment which implies considerable loss of SSA. The photocatalytic activity of the as-prepared powders was investigated by the degradation of the cationic dye methylene blue (MB). N-demethylation of the dye was clearly identified as one of the degradation pathways, while ring cleavage was only observed with crystalline samples. Crystallinity and SSA were crucial parameters for the photocatalytic activity of different samples of BiVO₄ depending on the pH of the solutions. The control of these two parameters during the synthesis of BiVO₄ qualifies this method for a potential large scale production.

Keywords: Nanocrystalline materials; Bismuth vanadate; Visible light photocatalysis; Methylene blue; N; -demethylation

The determination of the activities of different iron species in Fe-ZSM-5 for SCR of NO by NH₃ by Sandro Brandenberger; Oliver Kröcher; Arno Tissler; Roderik Althoff (pp. 348-357).

The activities of different iron species in Fe-ZSM-5 for the selective catalytic reduction (SCR) of NO by NH₃ were determined in terms of their turnover frequencies (TOF values). The relative concentrations of different species were correlated with their measured NO_x reduction efficiencies and NH₃ oxidation activities. Our results suggest that the SCR of NO by NH₃ is catalyzed by different active sites with different activation energies. At temperatures below 300°C, the SCR activity was observed to be primarily caused by monomeric iron sites; however, at T>300°C, T≥400°C and T≥500°C, the contribution of dimeric iron species, oligomeric species (e.g., trimeric and tetrameric iron species) and partially uncoordinated iron sites in the outmost layer of iron oxide particles, respectively, become important. The activation energies for monomeric and dimeric sites were evaluated to be about 36kJ/mol and 77kJ/mol, respectively. Due to their high activation energies, dimeric sites contributed more to the overall SCR activity at higher temperatures than did monomeric sites. The clustered sites not only contributed to the SCR activity but also caused nonselective oxidation of NH₃ at T≥350°C, whereas the dimeric species governed the NH₃ oxidation activity up to T=500°C. The TOF values for dimeric species were estimated to be 70±13s⁻¹ at 500°C. Monomeric sites were found to be completely inactive for NH₃ oxidation up to 500°C.

Keywords: SCR; Selective catalytic reduction; Ammonia; NO; _x; reduction efficiency; Fe-ZSM-5; Zeolite; Active sites

Noble metal-modified TiO₂ thin film photocatalyst on porous steel fiber support by Hongfan Guo; Marianna Kemell; Mikko Heikkilä; Markku Leskelä (pp. 358-364).

Through-porous steel fiber matrix with high specific surface area and self-support strength was examined as the support of TiO₂ film photocatalyst. TiO₂ was uniformly and conformally deposited onto the surface of the metal skeleton of the porous steel fiber matrix via atomic layer deposition method so that the porosity as well as gas permeability of the matrix is maintained. For further improving the photocatalytic activity, noble metals (Au and Pt/Pd alloy) were sputtered onto the surface of TiO₂ photocatalyst. The photodegradation of methyl orange was used for evaluating the photocatalytic properties. The results show that compared with TiO₂ films deposited on flat Si wafers, TiO₂ films on the porous support display higher photocatalytic activities, owing to their higher specific surface areas. The photocatalytic activity of TiO₂ on porous support was not enhanced by Au, while it was remarkably improved by Pt/Pd. The TiO₂ photocatalysts were also analyzed by scanning electron microscopy and X-ray photoelectron spectroscopy.

Keywords: Porous steel fiber; Atomic layer deposition; Sputtering; TiO; ₂; Photocatalysis

Highly valuable chemicals production from catalytic upgrading of radiata pine sawdust-derived pyrolytic vapors over mesoporous MFI zeolites by Hyun Ju Park; Hyeon Su Heo; Jong-Ki Jeon; Jeongnam Kim; Ryong Ryoo; Kwang-Eun Jeong; Young-Kwon Park (pp. 365-373).

The catalytic upgrading of pyrolytic vapors derived from radiata pine sawdust was carried out over mesoporous MFI zeolite synthesized using an amphiphilic organosilane. Its catalytic activity was compared with those of conventional HZSM-5 and mesoporous material from HZSM-5 (MMZ_ZSM-5). The effect of gallium incorporation into mesoporous MFI zeolite on the product distribution and chemical composition of bio-oil was also investigated. The catalysts synthesized were characterized using ICP, XRD, N₂-sorption, NH₃-TPD, and H₂-TPR methods. After catalytic upgrading, products were analyzed by GC–TCD, GC–FID, GC–MS, and Karl Fischer titration. The mesoporous MFI zeolite exhibited the best activity in deoxygenation and aromatization during the upgrading of pyrolytic vapors. In particular, mesoporous MFI zeolite showed high selectivity for highly valuable aromatics, such as benzene, toluene, and xylenes (BTX), even though it decreased the overall organic fraction of the bio-oil. The incorporation of gallium into the mesoporous MFI zeolite increased both the organic fraction of the bio-oil and resistance to coke deposition. Moreover, the selectivity for BTX aromatics was enhanced when the appropriate amount of gallium was introduced.

Keywords: Mesoporous MFI zeolite; Gallium; Catalytic upgrading; Fast pyrolysis; BTX aromatics

Nickel-grafted TUD-1 mesoporous catalysts for carbon dioxide reforming of methane by Xian-Yang Quek; Dapeng Liu; Wei Ni Evelyn Cheo; Hong Wang; Yuan Chen; Yanhui Yang (pp. 374-382).

The nickel active sites were introduced into TUD-1 mesoporous molecular sieve via grafting, direct synthesis, and impregnation methods. These samples were characterized using powder X-ray diffraction, N₂ physisorption, H₂ temperature-programmed reduction, H₂ chemisorption, TG/DTA, temperature-programmed hydrogenation, Raman spectra and transmission electron microscope to give the insight of physicochemical properties. Catalytic tests probed by the carbon dioxide reforming of methane revealed that Ni-grafted TUD-1 exhibited the highest catalytic activity and long-term stability among these catalysts. Further studies implied catalytic activity, stability and carbon formation were highly sensitive to the metallic nickel particle size which was significantly affected by the introduction method of Ni active sites. Strong anchoring effect inherent to the grafting method was suggested to be the underlying reason for the small Ni particle size and improved catalytic performance.

Keywords: TUD-1; Nickel; Grafting; Dry reforming

Effect of phase structures on the photocatalytic activity of surface fluorinated TiO₂ by Kangle Lv; Xiaofang Li; Kejian Deng; Jie Sun; Xianghong Li; Mei Li (pp. 383-392).

Nanocrystalline TiO₂ with different contents of anatase were tailored by hydrothermal treatment of the mixed solution of Ti(SO₄)₂ and TiCl₄ at 250°C for 24h, and then calcined at 500°C for 3h. The catalysts were characterized by X-ray diffraction, transmission electron microscopy, nitrogen sorption, X-ray photoelectron spectroscopy and UV–vis diffuse reflectance spectra. The as-prepared TiO₂ samples with different contents of anatase have similar BET specific surface areas (30–40m²/g) and crystalline sizes (30–40nm). The effect of surface fluorination on the adsorption and photocatalytic activity of TiO₂ samples was evaluated using Brilliant Red X3B, an anionic azo dye, as the target organic molecule at pH 3.0. Both on anatase and rutile TiO₂, the dark adsorption of X3B was greatly decreased in the presence of fluoride, ascribed to competitive adsorption of fluoride that reduces the positive charges on the catalyst surface. After surface fluorinated by 1.0mmol/L NaF, the photocatalytic activity of anatase was enhanced by a factor of 2.63. However, 81.3% of the photocatalytic activity was reduced for rutile TiO₂ after surface fluorinated under the same condition. Only when the content of anatase is higher than 40%, can fluoride shows positive effect on the photocatalytic activity of TiO₂. Two reaction models were put forward, based on the photocurrent response, degradation kinetics, hydroxyl radicals quenching and detecting, to illustrate the different effects of fluoride on the photocatalytic degradation of X3B in anatase and rutile TiO₂ suspensions.

Keywords: Photocatalytic degradation; Titanium dioxide; Fluoride; Adsorption; Crystalline phase

Photocatalytic performance of tetragonal and cubic β-In₂S₃ for the water splitting under visible light irradiation by Xianliang Fu; Xuxu Wang; Zhixin Chen; Zizhong Zhang; Zhaohui Li; Dennis Y.C. Leung; Ling Wu; Xianzhi Fu (pp. 393-399).

Tetragonal (T-In₂S₃) and cubic (C-In₂S₃) β-In₂S₃ were synthesized by hydrothermal method. The obtained products were characterized by X-ray diffraction (XRD), diffuse reflectance spectra (DRS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) technologies. Their photocatalytic activity for hydrogen evolution from water under visible light irradiation ( λ>400nm) was evaluated. It was revealed that the photocatalytic activity of β-In₂S₃ was strongly affected by the arrangement characteristic of the indium vacancies. The vacancy ordered T-In₂S₃ showed no activity for hydrogen production, while the vacancy disordered C-In₂S₃ exhibited stable activity. For C-In₂S₃ sample, further studies indicated that the photoactivity strongly depended on the nature and the amount of noble metal cocatalyst. The optimum loading value of Pt cocatalyst was found to be 2wt.%. With this loading amount as a reference value, the hydrogen production rate of noble-metal-loaded C-In₂S₃ decreased in the order Pd>Pt>Ru>Au/C-In₂S₃.

Keywords: In; ₂; S; ₃; Photocatalytic activity; Hydrogen evolution; Vacancy

Visible light photocatalytic reduction of Cr(VI) on TiO₂ in situ modified with small molecular weight organic acids by Nan Wang; Lihua Zhu; Kejian Deng; Yuanbin She; Yanmin Yu; Heqing Tang (pp. 400-407).

Visible light photoreduction of toxic Cr(VI) over TiO₂ was achieved through surface modification with small molecular weight organic acids (SOAs) as sacrificial organics. Because neat anatase TiO₂ is active only under UV light irradiation ( λ<387nm), no photoreduction of Cr(VI) was observed in TiO₂ dispersions being irradiated with visible light ( λ>420nm). However, when a small amount of colorless SOAs was added into the TiO₂ dispersion, a charge-transfer-complex (CTC) was formed between TiO₂ and SOA, which was sensitive to visible light irradiation and induced the photo-oxidation of SOA and photoreduction of Cr(VI). It was observed that about 95% of added Cr(VI) (0.2mmolL⁻¹) was removed in the visible light-illuminated TiO₂ (1.0gL⁻¹) dispersions at pH 3.0 within 2h by adding 0.2mmolL⁻¹ tartaric acid as a SOA. The SOA-induced photoreduction of Cr(VI) proceeded via a CTC-mediated path, being governed by chemical structures of sacrificial SOAs. A higher energy of the highest occupied molecular orbital or lower ionization potential of SOAs is favorable to electron transfer within TiO₂-SOA complex, thereby accelerating the photoreduction of Cr(VI). The Cr(VI) removal was further enhanced by increasing SOA concentration and/or decreasing solution pH.

Keywords: Visible light photocatalysis; Charger transfer complex; Organic acids; Dichromate

A new glass substrate photoelectrocatalytic electrode for efficient visible-light hydrogen production: CdS sensitized TiO₂ nanotube arrays by Jing Bai; Jinhua Li; Yanbiao Liu; Baoxue Zhou; Weimin Cai (pp. 408-413).

Transparent and visible-light-response CdS sensitized TiO₂ nanotube arrays (TNAs) photoelectrode was fabricated on conductive glass with the aim to improve the mechanical stability and light utilization of traditional Ti-foil-based titania nanotubes electrode. The sample was studied by FESEM, EDX and XPS to characterize its morphology and chemical compostion. UV–vis absorption spectra and photoelectrochemical measurement approved that the CdS coating enhanced the visible spectrum absorption of the TiO₂ nanotube array, as well as their solar-spectrum induced photocurrents. Under visible-light AM 1.5 illumination (100mW/cm²) the composite photoelectrode generate hydrogen from water containing sulfide ions at a rate of 1.12mL/cm²h, nearly 7.46 times higher than that of pure TNAs or 11.79 times than that of commercial P25 glass electrode. Such kind of material will has potential application in solar water splitting and other fields.

Keywords: Transparent; CdS; TiO; ₂; nanotube arrays; Hydrogen; Glass substrate electrode

Photocatalytic degradation of bisphenol-A by nitrogen-doped TiO₂ hollow sphere in a vis-LED photoreactor by Dewi Puspitaningrum Subagio; Madhavi Srinivasan; Melvin Lim; Teik-Thye Lim (pp. 414-422).

Photocatalytic degradation and mineralization of bisphenol-A (BPA) by a novel photocatalyst, nitrogen-doped TiO₂ hollow sphere (NhT), under blue, green and yellow lights emitted by light emitting diodes (LEDs) were investigated. The photocatalyst was synthesized through polystyrene spheres templating and treatment with ammonia to extend its light absorption properties to 550nm ( E_g=2.26eV) and meanwhile possess high porosity and specific surface area. Nitrogen incorporation was confirmed through XPS analysis indicating the presence of O–Ti–N or Ti–O–N linkages in the photocatalyst material. The NhT exhibited significant increase of BPA degradation and mineralization under blue, green and yellow lights as compared to the undoped TiO₂ hollow sphere, powder TiO₂, and Hombikat UV100. The photocatalytic degradation of BPA increased with pH, and the rate was the highest even at pH>p Ka1 of BPA (i.e., pH 9.6). At circumneutral pH, 90% of BPA was degraded in 2h under irradiation of blue light with NhT, while TOC removal was 66% after 6h of irradiation. The main aromatic intermediates formed were identified with GC/MS and LC/MS/MS as 4-hydroxyacetophenone, 4-isopropylphenol, 4-isopropenylphenol and isopropanolphenol. The pathways for BPA degradation under visible light appear to agree with those with UV/TiO₂.

Keywords: Nitrogen doping; Hollow spheres; Bisphenol-A; Photocatalytic degradation; Titania

Self-assembled hematite (α-Fe₂O₃) nanotube arrays for photoelectrocatalytic degradation of azo dye under simulated solar light irradiation by Zhonghai Zhang; Md. Faruk Hossain; Takakazu Takahashi (pp. 423-429).

Self-assembly aligned hematite (α-Fe₂O₃) nanotube arrays (α-Fe₂O₃ NTs) were successfully prepared on the Fe foils by a simple two-step electrochemical anodization method in NH₄F organic electrolyte. The α-Fe₂O₃ NTs electrodes were characterized by field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy, grazing incidence X-ray diffraction, UV–vis absorbance spectra, and X-ray photoelectron spectroscopy. The resulting α-Fe₂O₃ NTs showed a pore diameter of 40nm, thickness of 2μm, and a minimum wall thickness of ∼10nm. The systematic photoelectrochemical responses on the α-Fe₂O₃ NTs electrodes were presented. The maximum photoconversion efficiencies of 0.51% and 0.60% were collected at 0.3V under illumination of visible light and simulated solar light (AM 1.5G), respectively. The photoelectrocatalytic (PEC) and photocatalytic (PC) activities of the α-Fe₂O₃ NTs electrodes were evaluated by degradation of azo dye. The significant PEC and PC performance indicated that the α-Fe₂O₃ NTs electrodes were an effective photoelectrode under visible light and simulated solar light illumination.

Keywords: Hematite (α-Fe; ₂; O; ₃; ); Anodization; Nanotubes; Photoelectrochemical; Photoelectrocatalytic

Gold clusters supported on alkaline treated TS-1 for highly efficient propene epoxidation with O₂ and H₂ by Jiahui Huang; Takashi Takei; Tomoki Akita; Hironori Ohashi; Masatake Haruta (pp. 430-438).

Gold could be deposited as clusters smaller than 2.0nm in diameter on TS-1 by solid grinding (SG) of the support with dimethyl Au(III) acetylacetonate after TS-1 was pretreated in aqueous solution of alkaline metal hydroxides. While in C₃H₆ epoxidation with O₂ and H₂ mixture Au nanoparticles larger than 2.0nm deposited on TS-1 without alkaline treatment gave a very low PO formation rate of 11g_POkg_cat.⁻¹h⁻¹, Au clusters on alkaline treated TS-1 presented a greatly enhanced rate as high as 137g_POkg_cat.⁻¹h⁻¹, which was comparable to the best data reported so far. In addition, very high H₂ efficiency reaching 47% could be obtained by gold clusters on alkaline treated TS-1.

Keywords: Propene epoxidation; O; ₂; /H; ₂; mixture; TS-1; Alkaline treatment; Gold cluster; H; ₂; efficiency

Photocatalytic isomerization of norbornadiene to quadricyclane over metal (V, Fe and Cr)-incorporated Ti–MCM-41 by Ji-Jun Zou; Yi Liu; Lun Pan; Li Wang; Xiangwen Zhang (pp. 439-445).

The photoisomerization of norbornadiene using M–Ti–MCM-41 (M=V, Fe and Cr) has been studied to develop an alternative for solar energy accumulation and high energy aerospace fuel synthesis. The photocatalysts were prepared via hydrothermal method and characterized by EDX, XRD, N₂ adsorption–desorption, TEM, UV–vis, XPS and IR. With the same Si/M ratio in starting materials, the final concentration of V in the photocatalyst is significantly lower than that of Fe and Cr. V⁵⁺ and Fe³⁺ ions are highly dispersed in Si–O framework with tetrahedral coordination when the metal content is low, and the ordered structure is well retained. However, some species in higher coordination and polymerized environments present with increasing metal content, and the ordered structure becomes to collapse. Cr ions are difficult to get into the framework with various species like extraframework Cr⁶⁺ and bulk Cr₂O₃ formed, also the ordered structure is greatly destroyed. Under UV irradiation, the transition metal ions can improve the photoisomerization activity, with the order of V>Fe>Cr. The activities of V– and Fe–Ti–MCM-41 rise with the increase of Si/M ratio, whereas the performance of Cr–Ti–MCM-41 is irregular. The photocatalysts do not exhibit any activity under visible light, regardless of their absorption in visible-light region. The activity is closely related to the extent of dispersion and local structure of metal ions, about which an indirect excitation process of Ti–O species is suggested.

Keywords: Norbornadiene; Quadricyclane; Photocatalyst; M–Ti–MCM-41; Photoisomerization

Hydrogen production from butane steam reforming over Ni/Ag loaded MgAl₂O₄ catalyst by Harim Jeong; Misook Kang (pp. 446-455).

The intensive coke deposition and reforming at high temperature that occur in the case of the conventional Ni/γ-Al₂O₄ catalyst lead to rapid catalytic deactivation and reduced H₂ production from the hydrocarbon steam-reforming reaction. We used the impregnation approach to synthesize MgO (30wt%) Al₂O₄ catalysts loaded with bimetallic Ni(15mol%)/Ag(15mol%) or Ag/Ni and studied the steam reforming reactions of butane over these catalysts. The Ag-loaded catalyst exhibited significantly higher reforming reactivity compared to the conventional Ni/MgAl₂O₄ catalyst. The main products from steam reforming over the Ni/MgAl₂O₄ catalyst without the Ag component were H₂, CO, CO₂, and CH₄, with a small amount of C₂∼hydrocarbons. However, the addition of Ag reduced the degree of carbon deposition and improved the H₂ product selectivity by eliminating the formation of C₂∼hydrocarbons at temperatures below 750°C. The catalytic performances differed according to the order in which the added metal precursors were impregnated in each step. The H₂ production was maximized at 68% over Ni(9)/Ag(1)/MgAl₂O₄ at 700°C for 1h and this high performance continued for up to 53h.

Keywords: Hydrogen production; Butane steam-reforming reaction; Ag/Ni-loaded MgAl; ₂; O; ₄; Ni/Ag-loaded MgAl; ₂; O; ₄

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Applied Catalysis B, Environmental (v.95, #3-4)

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Applied Catalysis B, Environmental (v.95, #3-4)