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Applied Catalysis B, Environmental (v.73, #1-2)

IFC Editorial Board (pp. co2).

Editorial Board (pp. i).

Contents Continued (pp. ii).

Contents (pp. co4).

The SCR of NO with CH₄ over Co-, Co,Pt-, and H-mordenite catalysts by F. Lónyi; J. Valyon; L. Gutierrez; M.A. Ulla; E.A. Lombardo (pp. 1-10).

The catalytic reduction of NO with methane was studied operando in the presence and absence of oxygen in the reaction mixture over Co-, Co,Pt-, and H-mordenite (CoM, CoPtM, HM) catalysts using the coupled methods of diffuse reflectance infrared Fourier-transform spectroscopy and mass spectroscopy (Operando -DRIFTS-MS). The reaction temperature was in the 573–773K range, and the GHSV for nitric oxide was varied between 6000 and 60,000h⁻¹. In general, the Co-containing mordenite catalysts were more active than the HM. Over each catalyst two major surface intermediates were identified such as nitrosonium ion (NO⁺) and ammonia. The NO⁺ cations were shown to balance the negative charge on the zeolite framework. The NH₃ molecules were bound either coordinately to Lewis-acid site Co²⁺ ions or were protonated on Brønsted acid sites and retained by the zeolite as NH₄⁺ cations. The prevailing route of N₂ formation was found to involve the reaction of NO⁺ and NH₃ or NH₄⁺ surface species. It was shown that the surface concentration of the intermediate ammonia governed the rate of NO conversion. If O₂ was present in the feed gas it competed with the NO in the oxidation of methane and the surface intermediate ammonia. As a result, the steady-state concentration of the ammonia intermediate and the overall NO conversion to N₂ decreased. Additional routes of N₂ formation were revealed over the CoM and CoPtM catalysts. The cobalt facilitated the formation of NO⁺ and surface nitrate (NO₃⁻). Also nitrile (CN) and isocyanate (NCO) surface species were detected. The NO₃⁻ could be rapidly reduced by methane to intermediate NH₃ and, thereby, it increased the rate of NO conversion significantly. Nitrogen forming reactions can pass also through CN and NCO intermediates; however, the share of these reaction routes in the overall N₂ generation process was minor.

Keywords: NO; _x; abatement; Co,Pt-mordenite; Operando DRIFTS-MS; CH; ₄; /NO-SCR

Effect of key operating parameters on phenols degradation during H₂O₂-assisted TiO₂ photocatalytic treatment of simulated and actual olive mill wastewaters by Adrián M.T. Silva; Ekaterini Nouli; Nikolaos P. Xekoukoulotakis; Dionissios Mantzavinos (pp. 11-22).

The treatment of a synthetic solution containing 13 organic compounds typically found in olive mill wastewaters (OMW) by means of H₂O₂-promoted TiO₂ photocatalysis was investigated concerning the effect of major operating factors, namely catalyst type and loading, H₂O₂ dosage and method of addition, irradiation intensity, solution pH and initial substrate concentration on process efficiency. The latter was assessed in terms of individual compounds degradation (followed by high performance liquid chromatography), total phenols (measured according to the Folin–Ciocalteu protocol), chemical oxygen demand and total organic carbon decrease, decolorization and ecotoxicity. Of the various catalysts screened, Degussa Aeroxide P25 was found to be highly active for TPh degradation and therefore subsequent studies were performed using this catalyst. Experiments with the synthetic effluent at 650mg/L initial TPh concentration, H₂O₂ concentration in the range 0.073–0.118mol/L, 0.75g/L catalyst loading and 400W irradiation power led to complete TPh and color removal and 80% mineralization after 60min of reaction. The rate of degradation decreased with decreasing intensity from 400 to 250 to 9W and remained unchanged decreasing initial TPh concentration from 650 to 488 to 325 to 163mg/L indicating a zero order reaction regarding TPh. Changing the starting solution pH from 3.5 to 6 to 8 had only marginal effect on degradation which also generally decreased with decreasing catalyst loading and H₂O₂ concentration. The process was applied to treat actual OMW which were first filtered and diluted several times with water. Efficiency strongly depended on effluent composition and concentration; a 100-fold dilution was needed to make the effluent amenable to photocatalytic treatment.

Keywords: Photocatalysis; TiO; ₂; Phenols content; H; ₂; O; ₂; Olive mill wastewaters

Photoelectrochemical characterisation and photocatalytic activity of composite La₂O₃–TiO₂ coatings on stainless steel by M. Uzunova; M. Kostadinov; J. Georgieva; C. Dushkin; D. Todorovsky; N. Philippidis; I. Poulios; S. Sotiropoulos (pp. 23-33).

Composite La₂O₃–TiO₂ and plain TiO₂ photocatalytic coatings were prepared by a dip-coating technique on stainless steel substrates (SS) and tested as photoelectrodes in the electrically enhanced UV-photooxidation of organics. Electrode specimens were characterised by photovoltammetry under UV light in 0.1M K₂SO₄ solutions in the absence and presence of oxalate (a model organic pollutant), while larger electrodes were used in bulk photooxidation of oxalate and malachite green (a typical dye). La₂O₃–TiO₂/SS electrodes showed similar photocurrents to those of TiO₂ coatings on Ti substrates (TiO₂/Ti) and similar oxalate electro-photooxidation rates at moderate positive bias values. They also exhibited high removal rates for malachite green, but the electrochemical enhancement of its photooxidation was only observed at thin (0.5mgcm⁻²) and low La₂O₃ content (5mol% La) coatings.

Keywords: Titanium dioxide; Lanthanum oxide; Stainless steel; Photoelectrochemistry; Photooxidation

2,4-Dichlorophenoxyacetic acid (2,4-D) photodegradation using an M n⁺/ZrO₂ photocatalyst: XPS, UV–vis, XRD characterization by M. Alvarez; T. López; J.A. Odriozola; M.A. Centeno; M.I. Domínguez; M. Montes; P. Quintana; D.H. Aguilar; R.D. González (pp. 34-41).

Zirconium oxide materials doped with transition metals (Mn, Fe, Co, Ni and Cu) were synthesized using sol–gel methods. The powders, which were obtained, were characterized by XPS, XRD, UV–vis spectroscopy and nitrogen adsorption.The photodegradation of 2,4-dichlorophenoxyacetic acid (2,4-D), a herbicide used in agricultural applications, was used as a test reaction to study the activity of the compounds synthesized. Photodegradation studies were performed using a lamp radiating light with a UV wavelength of 254nm. Characterization studies showed a predominance of the tetragonal phase of zirconium oxide for all of the samples studied. The values obtained for the forbidden energy level E_g fall in a range between 3.6 and 5.5eV. BET surface areas were found to be in a range between 55 and 80m²/g. The concentration of the metals is small and in the case of Ni it could not be detected. Samples calcined at 400°C used in the photocatalytic study showed the highest activity. Mn/ZrO₂ was the most active photocatalyst used. A 70% conversion of 2,4-D was obtained in the first hour. This can be compared to a conversion of only 30% in the absence of Mn/ZrO₂.

Keywords: Photocatalysis; 2,4-Dichlorophenoxyacetic acid; XPS; Band gap; Tetragonal zirconia

Electrochemical promotion of platinum impregnated catalyst for the selective catalytic reduction of NO by propene in presence of oxygen by Fernando Dorado; Antonio de Lucas-Consuegra; Philippe Vernoux; José L. Valverde (pp. 42-50).

The effect of electrochemical promotion for the selective catalytic reduction of NO by propene was investigated, for the first time, on a Pt impregnated catalyst film directly deposited onto a Na–β″-Al₂O₃ solid electrolyte. The effect of sodium promoters on the activity and N₂ selectivity was evaluated at 240°C under different oxygen concentrations (0.5, 1 and 5%). The presence of promoters still enhanced the selectivity to N₂, even under large excess of oxygen (5%), where the N₂ reaction rate was increased by a factor of 1.8. Nevertheless, the promotional effect of sodium on the overall catalytic activity for NO removal was progressively lowered with increasing oxygen concentrations, as a result of a strong inhibition of propene adsorption and a relative increase of the oxygen coverage. Characterization by cyclic voltammetry supported these results, providing useful information about the chemisorption of reactant species under the different reaction conditions.

Keywords: Electrochemical promotion; NEMCA effect; Selective catalytic reduction; Platinum impregnated catalyst; Cyclic voltammetry

Pure versus metal-ion-doped nanocrystalline titania for photocatalysis by Panagiotis Bouras; Elias Stathatos; Panagiotis Lianos (pp. 51-59).

Thin films of pure or doped nanocrystalline titania have been deposited on glass slides by using a sol–gel procedure, in the presence of surfactant Triton X-100, which acts as template of the nanostructure. Fe³⁺, Cr³⁺ and Co²⁺ were used as dopants while the doping extended in a broad domain from very low to very high levels. The photocatalytic efficiency of pure or doped titania was tested for discoloration of an aqueous solution of Basic Blue 41. The presence of dopants resulted in a progressive loss of total crystallinity, some transition from anatase into rutile and, in the case of Co²⁺, formation of the mixed oxide cobalt titanate. Loss of anatase had dramatic consequences on photocatalytic efficiency by UV–vis excitation, which decreased fast with increasing dopant concentration. Selected visible excitation of the doped titania could lead to photodegradation of the dye but to a far lesser degree than UV–vis excitation. Photosensitization by absorption of light by the dye itself loses its importance in the presence of the dopant. Thus the doped material is a visible-light photocatalyst but substantial photodegradation efficiency is achieved only at very high doping levels, for example, 20at.% for Fe³⁺ doping. In any case, direct UV excitation of pure titania is a more efficient photocatalytic process than visible excitation of the doped semiconductor.

Keywords: Nanocrystalline titania; Metal-ion doping; Photocatalysis

Mn–Ce/ZSM5 as a new superior catalyst for NO reduction with NH₃ by Gabriela Carja; Yoshikazu Kameshima; Kiyoshi Okada; Changalla D. Madhusoodana (pp. 60-64).

Mn–Ce/ZSM-5 catalyst prepared in an aqueous phase at 423K exhibits a broad temperature window (517–823K) for high NO conversions (75–100%) in the process of selective catalytic reduction (SCR) by NH₃ even in the presence of H₂O and SO₂. Both the zeolite matrix and the over-exchanged amounts of manganese and cerium contribute to obtain a complex structure that owns microporous–mesoporous characteristics and specific surface properties.

Keywords: SCR; NO reduction; Manganese; Cerium; ZSM-5

The origin of the enhanced activity of Pt/zeolites for combustion of C₂–C₄ alkanes by T.F. Garetto; E. Rincón; C.R. Apesteguía (pp. 65-72).

The deep oxidations of ethane, propane and butane were studied on Pt supported on MgO, alumina, and zeolites KL, HY, ZSM5, and Beta. The catalyst activities were evaluated through both conversion versus temperature (light-off curves) and conversion versus time catalytic tests. The Pt oxidation activity for the three lower alkanes was drastically increased when supported on zeolites as compared to Pt/Al₂O₃ or Pt/MgO. C₂–C₄ alkane oxidation turnover rates were about two (ethane, propane) and one (butane) orders of magnitude higher on Pt/acid zeolites than on Pt/Al₂O₃, but also weakly acid Pt/KL zeolite was significantly more active as compared to Pt/Al₂O₃ (more than one order of magnitude for ethane and propane). This latter result showed that the support acidity is not a major contributing factor for lower alkane combustion. Promotion of the alkane oxidation activity on Pt/zeolites was explained by considering the drastic increase observed for the density of alkane adsorbed species on zeolite supports; it was found, in fact, that the alkane uptake per m² was about one order of magnitude higher on Pt/zeolites than on Pt/Al₂O₃. This alkane confinement in zeolite pores would enhance the Pt oxidation rate because the reaction is positive order with respect to the hydrocarbon and probably also because would promote an additional oxidation pathway in the metal-oxide interfacial region.

Keywords: Lower-alkanes combustion; Pt-based catalysts; Zeolite supports; Confinement effect

Reduction of nitrogen oxides over Ir/YSZ electrochemical catalysts by P. Vernoux; F. Gaillard; R. Karoum; A. Billard (pp. 73-83).

This study has shown that Ir/YSZ electrochemical catalysts can reach high catalytic activity for the SCR of NO by propene in the presence of oxygen. Under stoichiometric conditions, porous and thin (about 40nm) Ir film achieves N₂ yield higher than 80% between 350 and 500°C. However, iridium films require on-stream treatment at 500°C in order to develop their catalytic efficiency by increasing Ir particles size and establishing an ideal Ir⁰/IrO₂ ratio. Under lean-burn conditions, the same sample presents high and durable NO conversion at 500°C. These results confirm that magnetron sputtering is a suitable technique for synthesis of effective thin catalytic films. Furthermore, it was found that NO reduction by propene can be electrochemically promoted on Ir/YSZ electrochemical catalysts. This promotion exhibits an electrophobic NEMCA effect, the reaction rate increasing when a positive polarisation is applied. The electropromotion efficiency was found to be structure sensitive.

Keywords: Ir; YSZ; Electrochemical catalyst; Selective catalytic reduction; NO; Propene; Electrochemical promotion of catalysis; EPOC; NEMCA effect; Magnetron sputtering

Embedded Rh(1wt.%)@Al₂O₃: Effects of high temperature and prolonged aging under methane partial oxidation conditions by T. Montini; A.M. Condò; N. Hickey; F.C. Lovey; L. De Rogatis; P. Fornasiero; M. Graziani (pp. 84-97).

A simple and efficient synthetic procedure for the production of catalysts stable at high temperature was investigated. Methane partial oxidation was studied over a Rh(1wt.%)@Al₂O₃ catalyst, composed of Rh nanoparticles embedded in an Al₂O₃ matrix, and the results were compared with those of a reference Rh(1wt.%)/Al₂O₃, obtained by incipient wetness impregnation procedure. The embedded catalyst was prepared by precipitation of Al(OH)₃ in the presence of stabilised Rh nanoparticles, followed by calcination. H₂ chemisorption data confirm the accessibility of most of the protected Rh nanoparticles. Both Rh catalysts are active for MPO, reaching complete CH₄ conversion above 1023K. Notably, the embedded catalyst is more resistant to deactivation during consecutive run-up and steady state catalytic experiments. The protection offered by the surrounding layer of porous oxide prevents extensive sintering of the active metal phase, even after high temperature aging, as observed by high resolution TEM. Moreover, with respect to the standard impregnated sample, the embedded Rh(1wt.%)@Al₂O₃ is more resistant towards the undesirable incorporation of Rh into the alumina under oxidising conditions. At 1023K, stable MPO activity is observed for at least 60h, after which slow deactivation starts, essentially by coke deposition. Treatment with O₂ restores the catalytic activity, while brief switches to O₂ during reaction prevent deactivation. Increasing the working temperature or the reactant concentration significantly reduces the effects of coke deactivation.

Keywords: Rh catalyst; Embedded rhodium nanoparticles; Hydrogen production; Methane partial oxidation

Bi modified Pd/SnO₂ catalysts for water denitration by Jacinto Sá; Janine Montero; Elizabeth Duncan; James A. Anderson (pp. 98-105).

A Pd/SnO₂ catalyst was doped with low concentrations of Bi in order to induce selective poisoning of sites on the Pd surface in order to test a hypothesis that specific surface sites are responsible for ammonium formation during the catalytic hydrogenation of nitrates from drinking water. Initial addition of low levels of Bi appeared to selectively titrate high-energy surface Pd atoms located in the high index planes of the Pd crystallites. Addition of Bi had little effect on catalyst activity but modified selectivity profiles of nitrite and ammonium formation.

Keywords: Pd/SnO; ₂; Selective poisoning; Bi; Nitrate reduction; Aqueous; NH; ₄; ⁺; formation

Ethanol oxidation on a carbon-supported Pt₇₅Sn₂₅ electrocatalyst prepared by reduction with formic acid: Effect of thermal treatment by Flavio Colmati; Ermete Antolini; Ernesto R. Gonzalez (pp. 106-115).

A carbon supported Pt–Sn electrocatalyst in the Pt:Sn atomic ratio 75:25 was prepared by the reduction of Pt and Sn precursors with formic acid and thermally treated at 200°C (Pt–Sn200) and 500°C (Pt–Sn500). Thermal treatment at both temperatures gave rise to the formation of a predominant phase of cubic Pt₃Sn and, to a lesser extent, a hexagonal PtSn phase. The amount of the hexagonal PtSn phase as well as the particle size increased with increasing thermal treatment temperature. The formation of some very large particles (size>30nm) was apparent in the Pt–Sn500 catalyst. The activity for the ethanol oxidation reaction (EOR) and the performance in a single direct ethanol fuel cell (DEFC) of the catalyst thermally treated at 200°C were better than both the as-prepared catalyst and Pt₇₅Sn₂₅/C by ETEK. The higher activity for the EOR of the Pt–Sn200 sample was ascribed to the presence of the Pt₃Sn phase and to cleaning effect of the thermal treatment at 200°C.

Keywords: Pt–Sn alloys; Ethanol oxidation; Direct ethanol fuel cells; Thermal treatment

Hydrogen production from crude pyrolysis oil by a sequential catalytic process by Thomas Davidian; Nolven Guilhaume; Eduard Iojoiu; Hélène Provendier; Claude Mirodatos (pp. 116-127).

A sequential process aiming at hydrogen production was studied over two Ni-based catalysts, using crude beech-wood oil as the feed. The process alternates cracking/reforming steps, during which a H₂+CO rich stream is produced and carbon is stored on the catalyst, with regeneration steps where the carbon is combusted under oxygen. The two catalysts exhibited good performances for H₂ production from bio-oil, the gaseous products stream consisting in 45–50% H₂. The regeneration step was found fast and efficient, the coke being readily combusted and the catalyst activity fully recovered. A positive heat balance between the endothermic cracking/reforming reactions and the exothermic coke combustion suggests that an autothermal process could be designed. Comparison of the thermal decomposition of bio-oil (empty reactor) with the catalytic cracking revealed that they are first decomposed into primary light gases (CO, CO₂, CH₄, C₂₊) and soots. These compounds are further reformed onto the catalyst by the steam contained in bio-oil, and equilibrated via the WGS reaction. The key roles of the catalyst are therefore (i) to improve the overall bio-oil gasification into syngas, (ii) to promote steam reactions and increase hydrogen production by steam reforming and WGS and (iii) to control and determine the nature of the coke formed during the cracking/reforming step. A Ni/Al₂O₃ catalyst with large Ni particles was found to promote the formation of carbon filaments, whereas on a Ni–K/La₂O₃–Al₂O₃ catalyst, with a lower Ni loading and highly dispersed Ni, the carbon was essentially deposited as an amorphous carbon layer.

Keywords: Bio-oil; Pyrolysis oil; Hydrogen; Sequential catalytic cracking/reforming; Supported Ni; Coking; Regeneration

Tailor-made high porosity VOC oxidation catalysts prepared by a single-step procedure by J. Blanco; A.L. Petre; M. Yates; M.P. Martin; J.A. Martin; M.A. Martin-Luengo (pp. 128-134).

Supported platinum on sepiolite catalysts with high macroporosities have been prepared as conformed ceramic extrudates by a single-step synthesis route, designated impregnated carbon procedure (ICP), using activated carbon as a templating agent and also for in situ reduction of the metal salt. These catalysts display unique textural and mechanical features and highly dispersed Pt nanoparticles whose catalytic activities were evaluated in the combustion of trace toluene in air. The effects of the particle size, oxidation state and loading of platinum and of the reduction and calcination conditions on the catalytic activity were investigated.

Keywords: Toluene combustion; Platinum; Sepiolite; Activated carbon; Supported metal catalyst; Impregnated carbon procedure

Photocatalytic activity and photo-induced hydrophilicity of mesoporous TiO₂ thin films coated on aluminum substrate by Wingkei Ho; Jimmy C. Yu; Shuncheng Lee (pp. 135-143).

Mesoporous TiO₂ thin films were prepared on aluminum substrate via the reverse micellar method (RM-TiO₂) and sol–gel method (SG-TiO₂), respectively. It was found that the mesoporous RM-TiO₂ thin films exhibited a better photocatalytic performance than that of SG-TiO₂ in the degradation of acetone in air and photo-induced hydrophilicity. This was attributed to the fact that the RM-TiO₂ thin films had higher specific surface area and porosity than that of SG-TiO₂. The larger surface-to-volume ratio of mesoporous RM-TiO₂ thin films can serve as a more efficient transport path for gaseous reactants and products in photocatalytic reactions, thus improving the photocatalytic activity. The photocatalytic performance and hydrophilicity of RM-TiO₂ thin films coated on different substrates were also compared. The aluminium-supported samples showed a slower photocatalytic rate than those on quartz and stainless steel in the degradation of acetone because aluminum ions diffused from the substrate and acted as a charge recombination center. However, the hydrophilic property of the TiO₂/Al sample was superior to those on quartz and stainless steel substrates, probably due to its higher surface roughness and hydroxyl content.

Keywords: Mesoporous; Titanium dioxide; Thin films; Photocatalytic activity; Hydrophilicity

Electrochemical characterization of Pt-CeO₂/C and Pt-Ce_xZr1−_xO₂/C catalysts for ethanol electro-oxidation by Yuxia Bai; Jianjun Wu; Xinping Qiu; Jingyu Xi; Jianshe Wang; Jinfeng Li; Wentao Zhu; Liquan Chen (pp. 144-149).

Pt-CeO₂/C and a series of Pt-Ce_xZr1−_xO₂/C catalyst powders with different Ce/Zr ratio were prepared and evaluated in terms of the electrochemical activity for ethanol electro-oxidation using cyclic voltammetry (CV), steady state polarization experiments and CO-stripping technique at room temperature. XRD results show that Ce_xZr1−_xO₂ and Pt coexist in the Pt-Ce_xZr1−_xO₂/C catalyst and Ce_xZr1−_xO₂ has no effect on the crystalline lattice of Pt. TEM results show that the Pt and Ce_xZr1−_xO₂ particles dispersed uniformly over the surface of the carbon black. Cyclic voltammetry results show that the mass activity and specific activity of Pt-CeO₂/C for ethanol electro-oxidation is higher than that of Pt/C. The structure and Ce/Zr ratio of Pt-Ce_xZr1−_xO₂/C has effect on the catalytic activity of catalysts. CO-stripping voltammetry showed that the inclusion of CeO₂ and Ce_xZr1−_xO₂ favors the CO oxidation at lower potential.

Keywords: Ethanol electro-oxidation; Electrocatalyst; Ce; _x; Zr; 1−; _x; O; ₂; Pt-Ce; _x; Zr; 1−; _x; O; ₂; /C; Direct ethanol fuel cells

Pyrolysis of waste tyres with zeolite USY and ZSM-5 catalysts by Shen Boxiong; Wu Chunfei; Guo Binbin; Wang Rui; Liangcai (pp. 150-157).

Pyrolysis of waste tyres was carried out with a two-stage bed reactor. The waste tyres were first pyrolysed in a fixed bed reactor, and then the evolved pyrolysis gases were passed through a secondary catalytic reactor filled with two types of zeolite catalysts, which were ultrastable Y-type (USY) and ZSM-5 catalyst. The catalytic temperatures were examined to determine their influence on the yield of product from the pyrolysis–catalyst of waste tyres. The results indicated that with the increase of catalytic temperature, the gas yield increased at the expense of oil yield. The light fractions (<220°C) distilled from the derived oils with the two catalyst were analyzed by gas chromatography/mass spectrometry (GC/MS). It showed that there was a dramatic increase in the concentration of single ring aromatic compounds in the light fractions of the derived oils after catalysis. For example, toluene reached a value in the light fraction of 11.62wt%, benzene 1.6wt%, m/ p-xylene 12.27wt% and o-xylene 4.42wt%, with the catalysis of USY catalyst, at the pyrolysis temperature, catalysis temperature and catalyst/tyre ratio of 500, 400°C and 0.5, where the light fraction was about 71wt% in the derived oil. The yield of aromatic hydrocarbons in the derived oils were related to the different properties of the two catalysts such as the pore size which influenced the selectivity, and the silica/alumina (Si/Al) ratio which influenced the number of active sites on the catalyst surface.

Keywords: Pyrolysis; USY; ZSM-5; Tyre

Preparation and characterization of nickel–titanium composite xerogel catalyst for CO₂ reforming of CH₄ by H. Sun; H. Wang; J. Zhang (pp. 158-165).

The effects of the parameters of the sol–gel catalyst preparation such as hydrolysis ratio, acid/alkoxide ratio, and calcination temperature on surface area, porous structure, crystal structure and surface properties of nickel–titanium (Ni–Ti) composite xerogel catalyst were studied. The optimum hydrolysis ratio and acid/alkoxide ratio were determined under which conditions and 453K calcination temperature, a Ni–Ti xerogel catalyst with a surface area of 426m²/g was made. Increasing the calcination temperature would lead to dramatic decrease in surface area and collapse in porous structures. To compensate this deleterious effect, aluminum-containing compound was added into the precursor mixture in sol–gel preparation and the resultant Ni–Ti–Al composite xerogel catalyst had a significantly higher surface area even after undergoing a calcination temperature as high as 973K. This xerogel catalyst showed comparably high activity for carbon dioxide reforming of methane where high temperature calcination is inevitable.

Keywords: Nickel; Titanium; Aluminum; Sol–gel; Xerogel; Composite; Catalyst; Dry reforming

Single-crystalline TiO₂ nanorods: Highly active and easily recycled photocatalysts by Yuxiang Yu; Dongsheng Xu (pp. 166-171).

Large-scale and single-crystalline anatase TiO₂ nanorods were synthesized via hydrothermal reaction of H-titanate fibers. It was found that the pH plays an important role in the shape and crystal structures of the products by hydrothermal post-treatment of H-titanate fibers in acidic solutions. At pH 2–7, the pure anatase phase was formed and the samples reserved the rod-like morphology with a diameter of 20–200nm, in contrast to the formation of particles with a mixture of rutile and brookite phases at pH 0. Photocatalytic experiments indicated that the obtained single-crystalline anatase TiO₂ nanorods are highly active for photodegradation of organic pollutants. Furthermore, we demonstrated that these nanorod catalysts can be easily recycled without decrease of the photocatalytic activity.

Keywords: Photocatalysis; TiO; ₂; Nanorods; Single-crystal; Recycling

Nanocatalysts impregnated polythiophene electrodes for the electrooxidation of formic acid by V. Selvaraj; M. Alagar; I. Hamerton (pp. 172-179).

Conductive and porous polythiophene (PTh) films, which are used as host matrixes for Pt and Pt–Pd nanoparticles, are synthesized electrochemically. PTh films containing nanometer-sized Pt and Pt–Pd bimetallic particles are electro synthesized on an indium doped tin oxide (ITO) plate by voltammetric cycling between−0.2 and +1.4V (versus Ag/AgCl/3M NaCl). The ensuing PTh electrode, modified with nanoparticles, was probed for its catalytic activity towards the electrooxidation of formic acid, an industrially important material. The modified electrode exhibits significant eletrocatalytic activity towards the oxidation of formic acid and this may be attributed to (a) the uniform dispersion of nanoparticles in the PTh film and (b) the efficacy of the nature of Pd species in Pt–Pd bimetallic systems. Monometallic (Pt) and bimetallic (Pt–Pd) nanoparticles are found to be uniformly dispersed in PTh matrixes as confirmed from analytical data using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Energy dispersive X-ray analysis (EDAX) is used to characterize the composition of metal present in the nanoparticles modified electrodes.

Keywords: Electrocatalytic oxidation; Polythiophene; Platinum nanoparticles; Pt–Pd; bimetallic nanoparticles; Formic acid oxidation; Fuel cells

Pt, Ir and Pd promoted Co/MSU catalysts for hydrotreating of tetralin: A thiotolerance study by A. Infantes-Molina; J. Mérida-Robles; E. Rodríguez-Castellón; J.L.G. Fierro; A. Jiménez-López (pp. 180-192).

Cobalt based catalysts doped with noble metals (Pt, Ir or Pd) supported on Zr-MSU type materials were studied in the hydrogenation and hydrogenolysis/hydrocracking of tetralin at different temperatures. Sulphur tolerance was studied in order to evaluate the possible application of these catalytic systems in second stage processes. The catalytic test was carried out in a high-pressure fixed-bed continuous-flow stainless steel catalytic reactor operating at a pressure of 6.0MPa. Textural, structural, acidic and metallic properties were studied by XRD, XPS, H₂-TPR, NH₃-TPD, O₂ chemisorption measurements, TEM and elemental chemical analysis. Three catalysts were prepared with 10wt% of cobalt and 0.5wt% of noble metal (Pt, Pd or Ir). Moreover, other three monometallic noble based catalysts (0.5wt% of noble metal) were prepared to demonstrate the improvement found in the bimetallic ones. The results indicate that the presence of a noble metal in cobalt catalysts, especially Pt, improves their catalytic properties in hydrogenation reactions with or without dibenzothiophene (DBT) in the feed by operating not only at low contact times, but also at low H₂/THN molar ratios. The conversion values and the yield of hydrogenation products were higher for noble metal doped catalysts at all temperatures studied; meanwhile, the yield of hydrocracking and hydroisomerization compounds is appreciable at higher temperatures, especially for platinum and iridium catalysts, despite the formation of considerable amounts of undesirable naphthalene. The platinum promoted catalyst displays very good properties when DBT is added to the feed. After 10h on stream, with 600ppm of DBT in the feed and at 315°C, it was found to maintain its high conversion of tetralin (90.5%) and a yield of hydrogenation products of 82.2%.

Keywords: Mesoporous MSU; Cobalt catalysts; Tetralin hydrogenation; Hydrogenolysis/hydrocracking; Sulphur tolerance; Noble metals

Screening of catalysts and effect of temperature for kinetic degradation studies of aromatic compounds during wet oxidation by Rodrigo J.G. Lopes; Adrián M.T. Silva; Rosa M. Quinta-Ferreira (pp. 193-202).

Catalytic wet air oxidation (CWO) of six model phenolic acids: syringic, vanillic, 3,4,5-trimethoxybenzoic, veratric, protocatechuic and trans-cinnamic acid present in wastewaters from olive oil mills was studied at different temperatures. Experiments completed in the presence of four commercially available catalysts, CuO-MnO_x/Al₂O₃, CuO-ZnO/Al₂O₃, Fe₂O₃-MnO_x and CuO-MnO_x were compared with the ones related to various catalysts prepared in our laboratory (Ag-Ce-O, Mn-Ce-O, Mn-O, Ce-O). These catalysts showed a higher effective reduction of the total organic carbon (TOC) especially when the experiments were carried out with manganese oxide supported on ceria, an alternative and powerful catalyst to treat highly contaminated wastewaters containing phenolic compounds. Along the oxidation, acetic acid and phenol were detected and quantified by HPLC as the main intermediate species. Leaching, carbon adsorption as well as texture and morphology by SEM were analyzed and formation of whiskers at the catalyst surface was observed. Moreover, the kinetic parameters were obtained and co-oxidation of the phenolic compounds in the mixture was identified in our studies.

Keywords: Wastewater reaction engineering; Catalytic wet oxidation; Phenolic acids; Catalyst characterization; Kinetics

Fuel effects on the activity of silver hydrocarbon-SCR catalysts by Valérie Houel; Paul Millington; Raj Rajaram; Athanasios Tsolakis (pp. 203-207).

The hydrocarbon-SCR activity of Ag/Al₂O₃ has been correlated with the chain length of three model fuels ( n-octane, n-decane, n-dodecane) and with the alkane/aromatic composition of two fully formulated diesel fuels. The diesel fuels were US06 (ultra-low sulphur but 24wt.% aromatics) and Fisher–Tropsch Gas-to-Liquid (FT-GTL) (negligible sulphur and only 0.3wt.% aromatics). As the hydrocarbon chain length increases, the low-temperature NOx-conversion activity improves, while the reactant selectivity (hydrocarbon SCR versus hydrocarbon oxidation) decreases at higher temperatures. With diesel fuel, the catalyst initially achieves high NOx conversion at low temperature, but the conversion degrades with time due to coking. The rate of degradation is dependent on the nature of the hydrocarbons. Both the long-chain alkanes and the aromatics present in US06 diesel fuel promote the deposition of coke on the catalyst surface. However, high NOx conversion can be maintained using a fuel injection strategy that tunes the hydrocarbon/NOx ratio to the inlet temperature, so avoiding coking and improving both selectivity and fuel economy. At low temperatures the hydrocarbon/NOx ratio is kept low, and then increased as a function of temperature to compensate for the loss of hydrocarbon when the direct oxidation by O₂ begins to dominate. Optimisation of the fuel injection strategy is different for each type of fuel, but in general the NOx-conversion activity is higher for FT-GTL fuel at comparable hydrocarbon/NOx ratios.

Keywords: Ag; Hydrocarbon-SCR; NOx conversion; Coking; Diesel fuels

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Applied Catalysis B, Environmental (v.73, #1-2)

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Applied Catalysis B, Environmental (v.73, #1-2)