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Applied Catalysis A, General (v.292, #)

Inside front cover - Editorial Board (pp. co2).

Chemoselective hydrogenation of carbonyl compounds over heterogeneous catalysts by P. M�ki-Arvela; J. H�jek; T. Salmi; D.Yu. Murzin (pp. 1-49).

Chemoselective hydrogenation of unsaturated aldehydes and ketones over heterogeneous catalysts is a demanding task. The achieved selectivity levels depend both on the electronic and geometric structures of reactants and metal surfaces. Recent development in catalyst preparation, selection of new solvents, catalyst and reactor structures have been reviewed in this work. Additionally, catalyst characterization technique, especially alloy formation and in situ characterizations have been discussed in detail. The deep understanding of the catalyst structure is necessary for development of tailor-made catalysts for chemoselective hydrogenations. The state of art in both kinetic and molecular modelling used in chemoselective hydrogenations was presented. Some special features, like conversion–selectivity relationship and the performance in gas and liquid phase hydrogenations were discussed.

Keywords: Chemoselective hydrogenation; Unsaturated aldehyde; Heterogeneous catalyst

Investigation of sulfur behavior on CoMo-based HDS catalysts supported on high surface area TiO₂ by³⁵S radioisotope tracer method by Atsushi Ishihara; Franck Dumeignil; Danhong Wang; Xiangguo Li; Hisashi Arakawa; Eika W. Qian; Shinichi Inoue; Akinori Muto; Toshiaki Kabe (pp. 50-60).

Three series of CoMo catalysts (MoO₃: 6, 11, 16wt.%) with various Co/Mo molar ratios were prepared by successive incipient wetness impregnations of a titania sample previously prepared by the pH swing method, which provides a TiO₂ carrier with a high SSA (134m²g⁻¹) and excellent mechanical properties. DBT HDS activity of the catalysts increased with addition of cobalt up to Co/Mo=0.4 and then decreased for higher ratios, irrespective of the Mo loading. The results of a [³⁵S]DBT HDS method showed that S₀, the amount of labile sulfur atoms, increased in parallel with the activity when adding Co up to a molar ratio of 0.4. In contrast, unlike on CoMo/Al₂O₃ catalysts, only a slight increase in k_RE, the H₂S release rate constant, was observed upon Co addition. This was due to formation of the TiMoS phase: while formation of TiS^*Mo bonds favorably induces an increase in sulfur mobility on Mo/TiO₂ catalysts, electronic density on Mo atoms increases, which limits the promoting effect of Co on mobility of S_a sulfur atoms bridged between Mo and Co. Further, while the increase in HDS activity upon Co addition on a uniform MoS₂ monolayer on TiO₂ was in rather good agreement with the quantitative and kinetics data of the³⁵S tracer method, over MoS₂ slabs on TiO₂ this increase was larger than that expected from the results of the³⁵S tracer method. This was attributed to the presence of □^* and □_a CUS, i.e. catalytic sites that are not replenished with sulfur, at the steady state. A larger number of □^* CUS was present at low Mo wt.% or for low Co/Mo. As these particular catalytic sites are in the form of CUS at the steady state, they are not accounted by the [³⁵S] radiotracer method. This explains the differences observed between the experimental DBT HDS promotion and the promotion deduced from the increase in k_RE and S₀.

Keywords: Hydrodesulfurization; DBT; TiO; ₂; CoMo; ³⁵; S isotope tracer method

A hybrid supported nickel catalyst for the controlled radical polymerization of methyl methacrylate by Zhonghui Li; Hong Li; Yongming Zhang; Minzhao Xue; Lei Zhou; Yangang Liu (pp. 61-67).

A hybrid nickel-copper catalyst, which consists of a small ratio of copper catalyst and the supported nickel catalyst prepared by anchoring the nickel chloride on the cross-linking polyacrylate ion-exchange resin, has an effective catalytic activity for the polymerization of methyl methacrylate. The catalyst affords polymers with predetermined molecular weight and relatively narrow molecular weight distribution ( M_w/ M_n=1.26–1.67). The supported catalyst can be removed from the reaction medium by simple centrifugation with a low level of residual metal in the resulting polymer (5–7ppm Ni, 12–29ppm Cu). The supported nickel catalyst can be recycled conveniently with a relatively high catalytic activity without any regeneration treatment.

Keywords: Hybrid nickel-copper catalyst; Controlled radical polymerization

Effect of dealumination of zeolite catalysts on methylation of 2-methylnaphthalene in a high-pressure fixed-bed flow reactor by Jung-Nam Park; Jun Wang; Suk-In Hong; Chul Wee Lee (pp. 68-75).

Catalytic performances of various dealuminated zeolite catalysts such as H-mordenite (HM), H-beta (Hβ), USY and HMCM-22, for methylation of 2-methylnaphthalene (2-MN) were investigated in a high-pressure fixed-bed flow reactor. Methanol and 1,2,4-trimethylbenzene (TMB) were used as solvents and methylating agents. Dealumination of HM substantially improved 2-MN conversion, 2,6-dimethylnaphthalene (2,6-DMN) selectivity and stability. HM after the steam treatment at 550°C followed by acid leaching exhibited a high and a steady conversion of 40% with the very high 2,6-/2,7-DMN ratio of 2.4 for 5h of time on stream. In contrast, the untreated HM showed a severe deactivation, with a conversion of 8.4% and the 2,6-/2,7-DMN ratio of 1.4. On the other hand, Hβ showed very high and nearly steady conversion, but with reduced selectivity for 2,6-DMN; USY showed initially high conversion but the value decreased and there was no selectivity for 2,6-DMN; and HMCM-22 showed low but steady conversion with low selectivity for 2,6-DMN for 5h of time on stream. No promotion effect by dealumination on the conversion, stability, or selectivity was observed over Hβ, USY or HMCM-22. These distinguishing characteristics of these catalysts are discussed based on the differences in their porosity and acidity.

Keywords: Methylation; 2-Methylnaphthalene; Dimethylnaphthalene; Mordenite; Dealumination; Zeolite

Reductive routes to stabilized nanogold and relation to catalysis by supported gold by D. Boyd; S. Golunski; G.R. Hearne; T. Magadzu; K. Mallick; M.C. Raphulu; A. Venugopal; M.S. Scurrell (pp. 76-81).

Evidence is presented and discussed for the involvement of ionic gold, probably Au(1+) in catalysis by supported gold. Various catalytic systems and various experimental techniques have been used for reactions involving carbon monoxide. Mössbauer effect spectroscopy on gold-titania and gold-titania-zirconia reveals the co-existence of Au(0), Au(I) and Au(III), but only the Au(I) content correlates directly with the activity of these solids for CO oxidation. XPS data suggest that a small (ca. 6%) fraction of the gold present in gold-titania-zirconia catalysts is present in an electron deficient state relative to Au(0). For gold–iron oxide catalysts, high water-gas shift activity is obtained for samples in which a partial reduction of the gold, initially present as Au(III), has occurred. For gold-HY zeolites, in which the gold is initially introduced as Au(III) by ion-exchange from [Au(en₂)]³⁺, samples become catalytically active only after a considerable induction period has been exceeded. The induction period is shortened and the activity of the catalysts increased by pre-treatment with sodium borohydride, and some degree of reduction of the gold is assessed to have occurred. Further evidence that non-equivalent states of gold exist (i.e. metallic and ionic gold) in active CO oxidation catalysts based on gold-titania is provided by the fact that partial removal of gold occurs when the solids are treated with solutions containing cyanide ions under oxidative conditions. The specific activity per unit of gold increases with decreasing gold content when the gold content is lowered by such treatment. The results are consistent with the requirement for Au(I) involvement in the catalytic reaction, though a role for Au(0) is not ruled out.

Keywords: Catalytic systems; Carbon monoxide; Oxidative conditions

Vanadium effect on HUSY zeolite deactivation during hydrothermal treatment and cyclohexane model reaction by Hemiryan M.T. Oliveira; Marcelo H. Herbst; Henrique S. Cerqueira; Marcelo M. Pereira (pp. 82-89).

In the present paper, vanadium was ion-exchanged and impregnated at different levels on a HUSY zeolite. The vanadium effect on hydrothermal deactivation and coke formation is discussed based on cyclohexane model reaction data combined with spectroscopic characterization techniques. Coke formation is affected by vanadium introduction. For all catalysts the presence of vanadium increased the coke amount comparing to HUSY. During coke deactivation, a portion of vanadium was reduced from 5+ to 4+. The dehydrogenation products (benzene and olefins) preferentially form on vanadium sites, react further on the zeolite acid sites, resulting in an increase in the coke formation and thus on catalyst deactivation.

Keywords: Zeolite; USY; Deactivation; Coke; Vanadium; EPR

Efficient hydrogen supply from tetralin with superheated liquid-film-type catalysis for operating fuel cells by Shinya Hodoshima; Hiroaki Nagata; Yasukazu Saito (pp. 90-96).

A catalytic reaction pair, consisting of tetralin dehydrogenation/naphthalene hydrogenation, has newly been proposed as a storage medium of hydrogen for operating polymer-electrolyte fuel cells. The hydrogen storage capacity of tetralin (3.0wt.%, 28.2kg-H₂/m³) is lower than that of decalin (7.3wt.%, 64.8kg-H₂/m³), with the decalin dehydrogenation/naphthalene hydrogenation pair operated. Nevertheless, the rates of tetralin dehydrogenation and naphthalene hydrogenation to tetralin are much faster than the rates of the latter reaction pair. With respect to hydrogen storage for static or domestic use with space advantages, tetralin would be superior to decalin due to the ability of supplying hydrogen easily.Very high reaction rates and conversions of hydrogen evolution from tetralin were accomplished stationarily with “superheated liquid-film-type catalysis�? by heating at 210–240°C, in contrast to the poor results obtained with ordinary suspended catalysis. In particular, a carbon-supported nano-size platinum catalyst in the superheated liquid-film state exhibited efficient tetralin conversion as high as 95% within 25min contact at 240°C under distillation conditions. At the same temperature range, the dehydrogenation rates for decalin that had been obtained were ca. 3.9–6.3 times slower than those for tetralin, suggesting the excellent characteristics of tetralin as a hydrogen storage medium.In addition, carbon-supported nickel–ruthenium composite catalysts were found to give dehydrogenation activities at 240°C comparable with those of the platinum catalyst at 210°C.

Keywords: Hydrogen storage medium; Tetralin/naphthalene pair; Decalin/naphthalene pair; Carbon-supported nano-size metal catalysts; Superheated liquid-film-type catalysis

The strong influence of structures around titanium centers in dimeric mono-, di-, and tri-titanium(IV)-substituted Keggin polyoxotungstates on the catalytic epoxidation of alkenes with H₂O₂ by Chika Nozaki Kato; Satoshi Negishi; Kouichiro Yoshida; Kunihiko Hayashi; Kenji Nomiya (pp. 97-104).

Dimeric mono-, di-, and tri-titanium(IV)-substituted Keggin polyoxotungstates [(α-PTiW₁₁O₃₉)₂O]⁸⁻ (1), [(α-1,2-PW₁₀Ti₂O₃₈)₂O₂]¹⁰⁻ (2), and [(α-1,2,3-PTi₃W₉O₃₇)₂O₃]¹²⁻ (3) catalyzed the epoxidation of cyclooctene, cyclohexene, and 1-octene with aqueous H₂O₂ at 25°C in a homogeneous system. Structures around the titanium centers had a strong influence on the catalytic activities. Complex3, in particular, was the most active because it exhibited the fastest rate of formation of the active hydroperoxotitanium(IV) intermediate. The bond valence sum calculation of the oxygen atoms using the observed bond lengths revealed that protons in the countercations were bound to the surface edge-sharing oxygen atoms of each A–Ti₃ site in complex3, which accelerated the formation of the hydroperoxotitanium(IV) intermediate.

Keywords: Titanium(IV); Polyoxotungstate; Alkene epoxidation; Hydrogen peroxide; Oxidizing titanium(IV) intermediate

Preparation and characterisation of Rh/Al₂O₃ catalysts and their application in the adiponitrile partial hydrogenation and styrene hydroformylation by S. Alini; A. Bottino; G. Capannelli; A. Comite; S. Paganelli (pp. 105-112).

Rh/Al₂O₃ catalysts with a low metal loading were prepared using different preparation methods (ion exchange and homogeneous precipitation through urea decomposition). Catalysts with very high rhodium dispersion were obtained by properly choosing the preparation parameters. Moreover the kinetic parameters for the adsorption of the precursor on the support were determined. The catalysts were tested in two industrially important reactions: the adiponitrile hydrogenation and hydroformylation reaction of styrene. The hydrogenation of adiponitrile was carried out in mild conditions in a slurry reactor, at temperatures between 70 and 100�C and under a hydrogen pressure of 3MPa. The catalyst prepared with the ion exchange technique gave aminocapronitrile with a conversion of 60% and a selectivity of 99%. The catalyst was very active in the hydroformylation of styrene, but it suffered leaching problems such as many supported catalysts.

Keywords: Rhodium; Alumina; Ion exchange; Catalyst; Metal dispersion; Hydrogenation; Hydroformylation

Preparation of ZnNiMo/γ-alumina catalysts from recycled Ni for hydrotreating reactions by Carlos F. Linares; Julio L�pez; Adriana Scaffidi; Carlos E. Scott (pp. 113-117).

Ni, recovered from Ni–Cd cellular phone batteries, was used in the preparation of ZnNiMo/Al₂O₃ catalysts. The catalysts were characterized by temperature programmed reductions (TPR), surface area determinations (BET) and chemical analysis. Vanadyl octaethyl porphyrin (VOOEP) hydrodeporphyrinization (HDP) and thiophene hydrodesulfurization (HDS) were used as catalytic tests. It was found that the addition of Zn increases the ratio between octahedral and tetrahedral Mo in ZnMo and ZnNiMo catalysts, and that Ni addition lowers the reduction temperature of Mo species. Both results induce a positive synergetic effect for HDP and HDS reactions. An activity maximum was found for the catalyst with a Zn/(Zn+Ni) atomic ratio equal to 0.29, for both reactions. Finally, the use of a possible pollutant (Ni–Cd batteries) to produce a catalyst to eliminate contaminants in fuels was shown to be feasible.

Keywords: Ni–Zn–Mo Catalysts; Ni–Cd batteries; HDP; Tiophene HDS

Study of the deactivation of a commercial catalyst for ethylbenzene dehydrogenation to styrene by I. Rossetti; E. Bencini; L. Trentini; L. Forni (pp. 118-123).

The catalytic performance and characteristics of an industrial catalyst, fresh and spent, i.e. downloaded from an industrial reactor after a normal lifetime cycle, were compared. Some different causes of catalyst deactivation, such as loss or redistribution of promoters, active phase modification, Fe³⁺ reduction, coke deposition on catalyst surface and physical modifications, were evidenced by means of several techniques. All the mentioned causes of deactivation showed strictly interconnected and concurred to the decrease of conversion. However, the key factors leading to irreversible deactivation showed potassium migration towards the inner part of the extrudate particle, its agglomeration into concentrated spots and its volatilisation from the surface, together with the progressive Fe³⁺ reduction to Fe²⁺. These modifications led to the enhancement of coking activity and to the loss of mechanical properties, so making deactivation irreversible.

Keywords: Ethylbenzene dehydrogenation; Catalyst deactivation

Nanocomposite catalysts: Dendrimer encapsulated nanoparticles immobilized in sol–gel silica by Lindsey W. Beakley; Sarah E. Yost; Raymond Cheng; Bert D. Chandler (pp. 124-129).

A method for immobilizing dendrimer encapsulated nanoparticles (DENs) in a sol–gel silica matrix was developed. To evaluate timing effects for DEN addition to the sol–gel preparation, platinum DENs were added at two different times: (1) just before the condensation reactions were initialized, and (2) 24h after initializing the condensation reactions after the sol formation but before solutions had gelled. After gellation, drying, and activation, the catalysts had similar activities for CO oxidation catalysis. The catalyst prepared after sols had formed, however, was substantially less active for toluene hydrogenation. Infrared spectroscopy of adsorbed CO indicated that this latter catalyst had fewer available surface sites and that both catalysts remained poisoned by dendrimer decomposition products after activation.

Keywords: Pt catalysts; Sol–gel chemistry; PAMAM dendrimers; Dendrimer encapsulated nanoparticles; CO oxidation; Toluene hydrogenation; IR spectroscopy of adsorbed CO; Catalyst preparation

Catalytic pyrolysis of chlorodifluoromethane over metal fluoride catalysts to produce tetrafluoroethylene by Dae Jin Sung; Dong Ju Moon; Sangjin Moon; Joonho Kim; Suk-In Hong (pp. 130-137).

The catalytic pyrolysis of chlorodifluoromethane (CHClF₂, R22) over aluminum fluoride, calcium fluoride and their physical mixtures were investigated. The conversion of R22 and the selectivity of tetrafluoroethylene (TFE) over prepared catalysts were compared with those over a non-catalytic pyrolysis. The conversion of R22 in the catalytic pyrolysis was significantly higher than that in the non-catalytic case under the tested conditions. In the catalytic pyrolysis of R22, the selectivity for trifluoromethane (CHF₃, R23) decreased with time-on-stream (TOS), whereas the selectivity for tetrafluoroethylene (C₂F₄, TFE) increased. The Cu-promoted catalysts were more selective toward TFE than Cu-unpromoted catalysts. It was found that the enhanced TFE yield over Cu-promoted metal fluoride catalysts may be explained by the increased heat transfer effect. The physical mixture catalysts showed the highest selectivity and yield for TFE. This result may be interpreted as due to the surface modifications, such as the formation of bimetallic fluoride and the variation of fluorine content on the surface of catalyst, caused by the attack of HF produced during the pyrolysis of R22.

Keywords: Chlorodifluoromethane; Tetrafluoroethylene; Pyrolysis; Metal fluoride; Aluminum fluoride; Calcium fluoride; Catalyst

Preparation of La₂NiO₄/ZSM-5 catalyst and catalytic performance in CO₂/CH₄ reforming to syngas by W.D. Zhang; B.S. Liu; C. Zhu; Y.L. Tian (pp. 138-143).

A La₂NiO₄/ZSM-5 catalyst was prepared by the sol–gel method, which ensured high dispersion of the metal and high activity in the CO₂ reforming of methane. The catalytic performance, catalyst stability and coke deposition as well as the influence of the doped La species on the Ni/ZSM-5 catalyst were investigated. The results show that the conversion of CO₂ and CH₄ to syngas and the selectivity of CO and H₂ observed over the La₂NiO₄/ZSM-5 catalyst were significantly higher than those over a Ni/ZSM-5 or La₂NiO₄/γ-Al₂O₃ catalyst. Such results suggest that the doping of the rare earth ion (La³⁺) in the ZSM-5 not only enhanced the stability of the catalyst, but also increased the catalytic activity. In addition, the catalysts were characterized by X-ray diffraction (XRD), BET and thermogravimetic and differential thermal analysis (TG/DTA). The X-ray diffraction (XRD) studies revealed that the prepared catalyst, La₂NiO₄, exhibited a typical spinel structure and was uniformly dispersed both on the surface and in the ZSM-5 zeolite channels. During the CO₂/CH₄ reforming, the La₂O₃ generated from the La₂NiO₄ decomposition was transformed into La₂O₂CO₃ in an atmosphere of CO₂, which promoted CO₂ adsorption on the surface of the catalyst. The TG/DTA results indicate that the amount of carbon deposition on the La₂NiO₄/ZSM-5 catalyst was smaller than the amount on the Ni/ZSM-5 catalyst, and that there were at least two kinds of carbon deposition on the used La₂NiO₄/ZSM-5 catalyst. However, only one kind of carbon deposition existed on the used Ni/ZSM-5 catalyst.

Keywords: La; ₂; NiO; ₄; /ZSM-5 catalyst; Dispersion of Ni; Coke formation; Sol–gel technique; CO; ₂; /CH; ₄; reforming

Effect of combining palladium, iridium or rhenium with platinum supported on H-ZSM-5 zeolite on their cyclohexene hydroconversion activities by Ahmed K. Aboul-Gheit; Sameh M. Aboul-Fotouh; Noha A.K. Aboul-Gheit (pp. 144-153).

Cyclohexene (CHE) hydroconversion was investigated using catalysts containing 0.35wt.% Pt combined with 0.35wt.% of Pd, Ir or Re supported on H-ZSM-5 zeolite as a support in a flow-type reactor and using a current of hydrogen gas throughout a temperature range of 50–400°C. First, CHE was hydrogenated to cyclohexane (CHA) at relatively low temperatures, and dehydrogenated at relatively high temperatures to benzene passing through the formation of 1,3- and 1,4-cyclohexadienes (CHDEs). Moreover, CHE isomerises at intermediate temperatures to methylcyclopentenes (MCPEs), followed by their hydrogenation to methylcyclopentane (MCPA). Still at higher temperatures, CHE (and/or other products) suffer from hydrocracking to lower molecular weight hydrocarbons, beside alkylation of a portion of the formed benzene to toluene and xylenes. The kinetic parameters: activation energy and entropy were calculated to throw light on the nature of most important non-intermixing reaction (hydrogenation of CHE to CHA) using the monometallic and bimetallic catalysts.

Keywords: Catalysts, H-ZSM-5 zeolite; Cyclohexene hydroconversion

Study of the deactivation of Co- and Pt,Co-mordenite during the SCR of NO_x with CH₄ by L. Gutierrez; M.A. Ulla; E.A. Lombardo; A. Kov�cs; F. L�nyi; J. Valyon (pp. 154-161).

Co- and Pt,Co-mordenite catalysts were found to lose about 50% of their initial NO-reduction and CH₄-oxidation activity during a long catalytic NO_x-SCR test. Adsorption capacities for N₂, X-ray diffraction and Raman spectroscopic results suggested that the activity loss cannot be explained by either mordenite dealumination or extensive Co₃O₄ formation. Infrared spectra of the adsorbed pyridine showed that fresh catalysts have strong Br�nsted and Lewis acidity. The Br�nsted acidity was attributed to bridging OH groups of mordenite, formed from H₂O by heterolytic dissociation in the electric field around the Co²⁺ ions. During the catalytic reaction, a large fraction of both kinds of acid sites was lost. The drop of acidity and catalytic activity was explained by migration of the Co²⁺ ions to lattice positions where the ion is not accessible by pyridine and is coordinated by framework oxygen atoms only. High-pressure DRIFTS spectra of adsorbed N₂ and H₂-TPR results provided additional evidence of the connection between the deactivation and cation migration processes.

Keywords: Co- and Pt,Co-mordenite; Pyridine adsorption; Deactivation

Effect of variations in acid properties of HZSM-5 on the coking behavior and reaction stability in butene aromatization by Yueqin Song; Hongbing Li; Zhijun Guo; Xiangxue Zhu; Shenglin Liu; Xionglei Niu; Longya Xu (pp. 162-170).

In order to investigate the effect of acid properties on the coke behavior and stability of butene aromatization, we prepared the AHZSM-5 samples with various acid properties by the methods of hydrothermal treatment and K addition. The reaction of butene aromatization was carried out at 350°C and 0.5MPa in a continuous flow fixed bed. The characterization of the fresh/coked catalysts with NH₃-TPD, N₂ adsorption–desorption measurement, and TG techniques has shown that a large amount of acid sites (high acid density) of the AHZMS-5 catalyst can cause a large quantity of coke deposit and serious channel blockage, and so result in a rapid loss of aromatization activity. On the contrary, after a great reduction in strong acid sites of AHZSM-5 catalyst resulting from some K-modification, the presence of only many weak acid sites also could not lessen the formation of coke nor improve the reaction stability of butene aromatization. Interestingly, the simultaneous reduction in the strong and weak acid sites to a desirable level by hydrothermal treating the AHZSM-5 catalyst at a proper temperature can effectively suppress the coke formation and channel blockage, and thus improve its olefin aromatization stability.

Keywords: Butene aromatization; ZSM-5 zeolite; Hydrothermal treatment; Reaction stability; Acid properties

Selective low-temperature CO oxidation over Pt-Co-Ce/Al₂O₃ in hydrogen-rich streams by Tuğba İnce; Gökhan Uysal; A. Nilgün Akın; Ramazan Yıldırım (pp. 171-176).

The selective low-temperature oxidation of CO was studied in hydrogen-rich streams over Pt-Co-Ce/Al₂O₃ catalysts, which were prepared using the incipient to wetness co-impregnation technique. The effects of reaction temperature and feed composition on CO conversion and selectivity were investigated in a flow micro-reactor system. The 100% CO conversion was achieved over 1.4wt% Pt-1.25wt% Co-1.25wt% Ce/Al₂O₃ with significantly high selectivity at a reaction temperature of 90�C using a feed composition of 1.0% CO, 1.0% O₂, 60% H₂ and He as balance at a space velocity of 24,000cm³/(gh). Addition of 25% CO₂ and 10% H₂O into the feed increased the reaction temperature to 110�C but allowed 100% CO conversion for 300min time-on-stream. It was concluded that this catalyst may have great potential for removing CO in the hydrogen stream from a fuel processor for fuel cell applications, considering the fact that it may operate at significantly lower temperatures and O₂/CO ratios compared to other alternatives reported in the literature.

Keywords: Pt-Co-Ce/Al; ₂; O; ₃; catalyst; Selective CO oxidation; Fuel processor; Fuel cell

Low temperature catalytic partial oxidation of methane for gas-to-liquids applications by Stefan Rabe; Thanh-Binh Truong; Fr�d�ric Vogel (pp. 177-188).

The catalytic partial oxidation (CPO) of methane in the presence of steam (low temperature catalytic partial oxidation, LTCPO) over noble metal catalysts was investigated. The “dry�? CPO over ruthenium and rhodium catalysts was studied by thermogravimetric analyses coupled with IR spectroscopy. For CPO conditions, high CO selectivities at comparably low temperatures were observed for a rhodium/γ-alumina catalyst (5% rhodium) and a 1% ruthenium/TiO₂ catalyst giving evidence that a direct reaction mechanism is involved at low temperatures. It was found that under CPO conditions at low temperatures (<450°C) the catalysts are in an oxidised state, which is probably responsible for the formation of carbon dioxide. At higher temperatures, the catalysts are in a reduced state. The CO selectivity increases with the reduction of the catalyst. Our results indicate that a direct CO formation mechanism is also possible for ruthenium/alumina catalysts.The platinum catalysts studied in the LTCPO of methane were less active than rhodium and ruthenium catalysts and revealed a lower hydrogen yield. It was found that the steam reforming activity of the ruthenium/alumina catalyst was reduced inhibited by ceria. The long term stability (80h) of a ruthenium catalyst for LTCPO of methane was demonstrated.

Keywords: Ruthenium; Rhodium; Methane; Catalytic partial oxidation; Low temperature; GTL

Deactivating effect of quinoline during the methylcyclohexane transformation over H-USY zeolite by G. Caeiro; Patrick Magnoux; J.M. Lopes; F. Ram�a Ribeiro (pp. 189-199).

The influence of 0.5wt.% of quinoline (540ppm of nitrogen) in the feed was tested for the methylcyclohexane transformation at 350�C over an H-USY zeolite (framework Si/Al ratio of 5.4). The selectivities for the fresh catalyst do not seem to be altered by the presence of quinoline. Oppositely, for the deactivated zeolite, the aromatics yield increases for the tests performed with quinoline. Deactivation with time on stream is very pronounced, even for tests carried out without the base molecule; this can be attributed to the formation of highly polyaromatic coke molecules that block the acid sites and the microporous structure. In presence of quinoline, deactivation is enhanced due to its cumulative poisoning effect, especially for smaller contact times. This deactivation is caused by the strong interaction of the nitrogen base with the Br�nsted acid sites responsible for the cracking mechanism. Quinoline molecule also participates in coke formation reactions, leading to an increase in the produced amount of coke, particularly of the more polyaromatic compounds insoluble in dichloromethane.

Keywords: H-USY zeolite; Cracking; Methylcyclohexane; Quinoline; Poisoning; Deactivation; Coke

Investigation of factors influencing catalytic activity for n-butane isomerization in the presence of hydrogen on Al-promoted sulfated zirconia by Yinyong Sun; St�phane Walspurger; Beno�t Louis; Jean Sommer (pp. 200-207).

Two series of Al-promoted sulfated zirconia with 3mol% Al₂O₃ content were prepared. In one case, zirconium–aluminum hydroxide has been aged at room temperature; in the other case, zirconium–aluminum hydroxide has been synthesized at 373K under hydrothermal condition. For the two series of samples, the influence of the synthesis parameters such as ageing time, the amount of ammonia added, and zirconium concentration on catalytic activity for n-butane isomerization in the presence of hydrogen were investigated. Moreover, Al-promoted sulfated zirconia with a high surface area (174m²/g) can be obtained by properly adjusting synthesis parameters under hydrothermal condition at 373K. The catalytic data showed that this material had similar catalytic activity to a conventional Al-promoted sulfated zirconia with a low surface area (98m²/g). The characterization of the samples revealed that the catalytic activity was directly correlated with sulfur content rather than surface area, sulfate density and the total number of Brønsted acid sites. The synthesis of the precursors of hydroxides before sulfation is a crucial step for catalytic activity of the samples in n-butane isomerization.

Keywords: H/D exchange; Sulfated zirconia; n; -Butane; Isobutane; Hydrogen; Isomerization; Hydrothermal synthesis

Mg,Al-mixed oxide system: Synthesis under hydrothermal conditions, physico-chemical characterisation and application as an efficient catalyst for imidazole methylation by Hanna Grabowska; Mirosław Zawadzki; Ludwik Syper; Włodzimierz Miśta (pp. 208-214).

Mg,Al-mixed oxide catalyst with molar ratio 1:2 was prepared hydrothermally from magnesium acetate and basic aluminium nitrate. The obtained sample was characterised by XRD, HRTEM and nitrogen adsorption. The basic sites density was determined by temperature-programmed desorption of CO₂ combined with mass spectrometry (TPD-MS). Moreover, test reactions for acid–base characterisation (i.e. 2-propanol and cyclohexanol transformations) were used. The prepared catalyst proved to be selective and active for monoalkylation of imidazole leading to 1-methylimidazole. The gas phase catalytic alkylation of imidazole with methanol on Mg,Al-mixed oxide catalyst was carried out in a continuous process at atmospheric pressure in the temperature range of 225–350°C. 1-Methylimidazole was efficiently obtained with selectivity reaching up to 97.4% at an imidazole conversion of 93.0% (at temperature 340°C).

Keywords: Mg,Al-mixed oxide; Hydrothermal synthesis; Imidazole; Alkylation; Methanol; 1-Methylimidazole

Transformation of methanol in the presence of steam and oxygen over ZnO-supported transition metal catalysts under stream reforming conditions by Nobuhiro Iwasa; Masayoshi Yoshikawa; Wataru Nomura; Masahiko Arai (pp. 215-222).

Steam reforming of methanol (CH₃OH+H₂O→3H₂+CO₂) has been investigated with various ZnO-supported group 8–10 metal catalysts in the presence of oxygen. The catalysts may be classified into two groups according to their catalytic actions and properties. One group includes Pd/ZnO and Pt/ZnO catalysts, which are active for the steam reforming in the absence of oxygen. In the presence of oxygen, however, partial oxidation of methanol (CH₃OH+(1/2)O₂→2H₂+CO₂) rapidly proceeds and the conversion of methanol into hydrogen is drastically enhanced. These catalysts are composed of PdZn and PtZn alloys, which catalyze the steam reforming and the partial oxidation of methanol in the absence and presence of oxygen, respectively. In addition, for Pd/ZnO catalysts, high Pd loading favors the partial oxidation, whereas lower Pd loading is beneficial to the oxidation of methanol similar to the second group of catalysts. The second group includes other group 8–10 metal catalysts such as Fe, Co, Ni, Ru and Ir, which have no alloy components, in contrast to the first group. The decomposition of methanol (CH₃OH→2H₂+CO) occurs with these catalysts in the absence of oxygen in preference to the steam reforming. In the presence of oxygen, the oxidation of methanol (CH₃OH+(3/2)O₂→2H₂O+CO₂) occurs predominantly and the production of hydrogen is not so improved, although the total conversion of methanol is increased.

Keywords: Steam reforming; Methanol; Hydrogen production; Oxygen; Pd alloy

Catalytic oxidation of cyclohexane to cyclohexanol and cyclohexanone over Co₃O₄ nanocrystals with molecular oxygen by Lipeng Zhou; Jie Xu; Hong Miao; Feng Wang; Xiaoqiang Li (pp. 223-228).

Co₃O₄ nanocrystals with average particle sizes of 30 and 50nm were synthesized using cobalt nitrate as precursor, and were characterized by X-ray diffraction (XRD), nitrogen adsorption, transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR) spectroscopy. Catalytic oxidation of cyclohexane with molecular oxygen was studied over Co₃O₄ nanocrystals. These catalysts showed obviously higher activities as compared to Co₃O₄ prepared by the conventional methods, Co₃O₄/Al₂O₃, or homogeneous cobalt catalyst under comparable reaction conditions. The 89.1% selectivity to cyclohexanol and cyclohexanone at 7.6% conversion of cyclohexane was realized over 50nm sized Co₃O₄ nanocrystals at 393K for 6h.

Keywords: Nanocrystals; Co; ₃; O; ₄; Cyclohexane; Oxidation

Low temperature water-gas shift: Examining the efficiency of Au as a promoter for ceria-based catalysts prepared by CVD of a Au precursor by Gary Jacobs; Sandrine Ricote; Patricia M. Patterson; Uschi M. Graham; Alan Dozier; Syed Khalid; Elin Rhodus; Burtron H. Davis (pp. 229-243).

Increasing the Au loading had a significant positive impact on the catalytic activity. The partial reduction of ceria is necessary for generating bridging OH groups on the surface of ceria, which serve as the active sites. The surface shell reduction process in H₂ was monitored by TPR, XANES, and in situ DRIFTS spectroscopy. Either the oxygen deficiencies are first formed, followed by dissociative adsorption of H₂O to generate the Type II bridging OH groups or, they may be formed directly by spillover of dissociated H₂ from the metal to the ceria surface. For each pair of bridging OH groups formed, two cerium atoms in the surface shell change from the Ce⁴⁺ to Ce³⁺ oxidation state. Addition of Au facilitates the surface reduction process and thereby decreases the reduction temperature from 450°C for the unpromoted catalyst to 100°C for the 5% Au/ceria catalyst. A systematic decrease in the required temperature for ceria surface shell reduction was observed by increasing the Au promoter loading as follows: 0.1, 0.25, 0.5, 1, 2.5, 5%.Gold and platinum promoted catalysts were compared in a suitable reaction temperature range after first ensuring that metal–oxide interactions were overcome (ca. 5% metal loading). Approximately 20 times the amount of 5% Au/ceria catalyst was required to achieve a lightoff curve similar to that of a 5% Pt/ceria in the temperature range 200–300°C, and 5% Pt/ceria also exhibited higher steady-state activity (about double that of Au) at 175°C. This result suggests that, in addition to the role the metal plays in facilitating the formation of the active site bridging OH groups, it also influences the intrinsic rate of the WGS reaction. Transient formate decomposition experiments carried out at 140°C indicated that the rate of formate decomposition was approximately 20 times higher for 2.5% Pt/ceria than that of 2.5% Au/ceria, suggesting that the metal (in addition to the promoting effect of H₂O previously reported) plays a role in facilitating the decomposition of surface formate intermediates, the proposed rate limiting step of the reaction mechanism.

Keywords: Au loading; Au/ceria catalyst; Pt/ceria catalyst

Modification of the catalytic behaviour of platinum by zinc in crotonaldehyde hydrogenation and iso-butane dehydrogenation by J. Silvestre-Albero; J.C. Serrano-Ruiz; A. Sep�lveda-Escribano; F. Rodr�guez-Reinoso (pp. 244-251).

The effect of the presence of zinc on the catalytic behaviour of platinum in the vapour phase hydrogenation of crotonaldehyde (2-butenal) and in iso-butane dehydrogenation has been determined in activated carbon-supported catalysts prepared using H₂PtCl₆ and Zn(NO₃)₂ as the metal precursors. The catalysts have been characterised by temperature-programmed reduction (TPR), adsorption microcalorimetry of CO at room temperature and X-ray photoelectron spectroscopy after in situ reduction at 773K. The bimetallic catalyst, with a bulk Zn/Pt atomic ratio of 13.7, showed a much higher initial activity in crotonaldehyde hydrogenation, although it deactivated more strongly with time on stream. Lower activation energy for this reaction was also obtained, as well as a higher selectivity towards the unsaturated alcohol. On the other hand, the catalytic behaviour for iso-butane dehydrogenation was greatly improved by the presence of zinc, the bimetallic catalyst being more active than its monometallic counterpart and showing 100% selectivity to iso-butene.

Keywords: Pt-Zn; Selective hydrogenation; Dehydrogenation; Adsorption microcalorimetry; XPS

Multi-functional alumina–silica bimodal pore catalyst and its application for Fischer-Tropsch synthesis by Yi Zhang; Masahiko Koike; Ruiqin Yang; Sukamon Hinchiranan; Tharpong Vitidsant; Noritatsu Tsubaki (pp. 252-258).

A multi-functional bimodal pore catalyst support, alumina–silica bimodal pore support, was prepared from a polymer complex solution and silica gel. The obtained bimodal pore support had two kinds of main pores; the pore volume was decreased and the specific surface area was enlarged, comparing with the original silica gel. This kind of bimodal pore support was applied in slurry phase Fischer-Tropsch synthesis, where cobalt was supported as active metal. Alumina–silica bimodal pore catalyst exhibited high catalytic activity and favorite selectivity, due to the spatial effects of bimodal pore structure and chemical effects of coexisting alumina, which formed the new small pores inside SiO₂ large pores. Alumina–silica bimodal pore catalyst showed higher activity than silica–silica bimodal pore catalyst with similar pore structure, proving that hetero-atom bond between alumina and silica was important to promote the performance of the dispersed cobalt. The various catalysts were characterized by XRD, chemisorption, in situ DRIFT, TPR, and TPSR. It was found that alumina in alumina–silica bimodal structure improved cobalt dispersion significantly while keeping the reduction degree almost the same. TOF of alumina–silica bimodal catalysts was the highest, supported by the largest bridge-type adsorbed CO peak in DRIFT observation of this catalyst, as bridge-type adsorbed CO was the active intermediate in FTS.

Keywords: Bimodal pore support; Alumina; Fischer-Tropsch synthesis; Cobalt catalyst; Syngas

Ruthenium(III)-catalyzed mechanistic investigation of oxidation of an azo dye by sodium N-haloarenesulfonamidates in acid medium: A comparative spectrophotometric kinetic study by Puttaswamy; R.V. Jagadeesh (pp. 259-271).

The kinetics of ruthenium(III) chloride (Ru(III))-catalyzed oxidation of p-hydroxyazobenzene (PHAB) by sodium N-haloarenesulfonamidates or N-haloamines (RNXNa, where R=CH₃C₆H₄SO₂ or C₆H₅SO₂ and X=Cl or Br): chloramine-T (CAT), chloramine-B (CAB), bromamine-T (BAT) and bromamine-B (BAB) in HCl medium at 298K has been spectrophotometrically investigated at λ_max=347nm. UV–vis spectrophotometry was used as a basic analytical approach in this study. Under comparable experimental conditions, the oxidation reaction follows identical kinetics with first-order dependences on [oxidant]₀, on [PHAB]₀ and on [Ru(III)], and less than unity order dependence on [H⁺]. Additions of halide ion (Cl⁻ or Br⁻) and reduction product ( p-toluenesulfonamide or benzenesulfonamide) have no significant effect on the rate. The stoichiometry of the title reaction was found to be 1:2 and the oxidation products were identified as p-nitrosophenol and p-nitrosobenzene by GC–MS. The reaction rate was found to decrease with increases in ionic strength of the medium and increases in solvent polarity (dielectric constant). Proton inventory studies made in a mixture of H₂O–D₂O indicated the participation of H⁺ ion in the formation of transition states. The reaction fails to initiate the polymerization of acrylonitrile. The activation parameters for the reaction were deduced from Arrhenius plots. The rates with bromamines were found to be higher than those with chloramines by a factor of 3; the rates follow the sequence: BAB>BAT>CAB>CAT. This effect is attributed to electronic factors. The calculated isokinetic temperature ( β) of 354K obtained from enthalpy–entropy relationships and Exner correlations was much higher than the experimental temperature of 298K, indicating that the rate is under enthalpy control; a similar mechanism operates in the oxidation of PHAB by all the four oxidants. Under the identical set of conditions, the kinetics of Ru(III)-catalyzed oxidation of PHAB by N-haloamines has been compared with uncatalyzed reactions, revealing that the catalyzed reactions are seven- to nine-fold faster. The catalytic constant ( K_C) has been calculated for each oxidant at different temperatures. The values of activation parameters with respect to the catalyst have been evaluated from the plots of log K_C versus 1/ T. Some spectroscopic evidence for the formation of 1:1 complex between PHAB and Ru(III) has been obtained. The observed results have been explained by a plausible mechanism and the related rate law has been deduced.

Keywords: Ru(III); Catalysis; Oxidation-kinetics; p; -hydroxyazobenzene; N; -haloamines

Performance of NiO–MgO solid solution-supported Pt catalysts in oxidative steam reforming of methane by Mohammad Nurunnabi; Baitao Li; Kimio Kunimori; Kimihito Suzuki; Ken-ichiro Fujimoto; Keiichi Tomishige (pp. 272-280).

The effect of Pt addition to NiO–MgO solid solution catalysts on the performance in oxidative steam reforming of methane was investigated. In the oxidative reforming of methane, Pt/NiO–MgO gave much higher methane conversion than NiO–MgO and Pt/MgO, especially under short contact time (low W/ F: W=catalyst weight, F=total flow rate). Although the effect of Pt was not clear in temperature program reduction profiles, the additive effect of Pt is remarkable in oxidative reforming of methane in term of catalyst activation. In the case of Pt/NiO–MgO catalysts, even when the H₂ reduction pretreatment was not done, the catalyst can be activated at a temperature higher than 773K with a reactant gas including methane, steam, or oxygen. This behavior is related to the methane combustion activity. The order of the activity was as follows: Pt/NiO–MgO≫Pt/MgO>NiO–MgO. High combustion activity is related to methane activation ability, and this can make the catalyst activation and reduction easier.

Keywords: Oxidative steam reforming of methane; Pt; Ni; Self-activation; NiO–MgO solid solution

Reusability of the Cu/Ni-based colloidal catalysts stabilized by carboxylates of alkali-earth metals for the one-step amination of dodecyl alcohol and dimethylamine by Hiroshi Kimura; Shun-Ichi Tsutsumi; Kiyoshi Tsukada (pp. 281-286).

The Cu/Ni-based colloidal catalyst, stabilized by barium stearate (Cu:Ni:Ba mole ratio 5:1:1; particle size 1–5nm), for the one-step amination of dodecyl alcohol and dimethylamine to N, N-dimethyldodecylamine at Cu concentration ranges of 300–1000ppm at 200–210°C, could be recovered by distillation and could be reused several times without a decrease in the activity. The activity of the concentrated activated colloidal catalysts for the amination reaction was not decreased for a month. These observations demonstrated that the reusability and stability of the Cu/Ni-based colloidal catalysts were enough for the commercial operation, which opposed to the claim that a colloidal catalyst cannot be recovered and reused. The Cu/Ni/Ba colloidal catalyst is the first example of a metallic colloid applied for the amination reaction.

Keywords: Amination; Cu/Ni/Ba

On the effects of calcination conditions on the surface and catalytic properties of γ-Al₂O₃-supported CoMo hydrodesulfurization catalysts by Y.S. Al-Zeghayer; B.Y. Jibril (pp. 287-294).

A series of alumina-supported cobalt-molybdenum catalysts were prepared by the incipient-wetness method. Different calcination temperatures (673–873K) and durations (2–96h) were used to obtain the catalysts. Samples of the catalysts were characterized by X-ray photoelectron spectroscopy (XPS). Depending on the calcination condition, two forms of molybdenum (Mo⁴⁺ and Mo⁶⁺) and sulfur (S₁ and S₂) were identified. The ratio of Mo⁴⁺/Mo⁶⁺ appeared to be affected more by the duration than by the calcination temperature. However, increase in the calcination temperature (673–873K) led to an increase in the amount of cobalt interacting with the alumina support, with a corresponding decrease in Co-Mo-S ensembles. The catalysts were tested in hydrodesulfurization of dibenzothiophene (DBT). The catalyst with 24h calcination time exhibited the highest DBT conversion. For the catalyst at a conversion of 38.8%, biphenyl (BP) and cyclohexylbenzene (CHB) were produced with selectivities of 82.8 and 17.2%, respectively. When either the calcination temperature or duration was increased, a smaller amount of CHB was observed. This has been associated with changes in the catalysts’ surface properties.

Keywords: H; ydrodesulfurization; Dibenzothiophene; CoMo/Al; ₂; O; ₃; Calcination Biphenyl; Cyclohexylbenzene; X-ray photoelectron spectroscopy

Catalytic partial oxidation of methane to syngas over Ca-decorated-Al₂O₃-supported Ni and NiB catalysts by L. Chen; Y. Lu; Q. Hong; J. Lin; F.M. Dautzenberg (pp. 295-304).

One wt% Ni and 1wt% NiB catalysts supported on Ca-decorated γ-Al₂O₃ (Ca-AlO) supports were prepared by conventional impregnation and chemical reduction methods. These supported catalysts were applied for the catalytic partial oxidation of methane (POM) to syngas. The two low-Ni-loading catalysts have shown high activity/selectivity for the POM, as good as those of 1wt% Rh and 10wt% Ni catalysts supported on commercial γ-Al₂O₃ support (AlO). But their coking resistivity was remarkably better than that of 10wt% Ni/AlO. The coke formation over these catalysts decreased in the following order: 10wt% Ni/AlO≫1wt% Ni/Ca-AlO>1wt% NiB/Ca-AlO∼1wt% Rh/AlO. The key factor in the improvement of the carbon resistance was to decrease the metallic Ni particle size through the lowering of Ni loading combined with the addition of B promoter. The low Ni loading has been achieved by covering the support with a CaAl₂O₄ layer, and decreasing the catalyst calcination temperature to ∼723K. The formation of crystalline carbon was greatly suppressed on the NiB catalysts due to the highly dispersed nature; such formation significantly improved the thermal stability of the Ni particles.

Keywords: Methane; Partial oxidation; Syngas; Ni catalyst; Boron; Coke

Facile clay-induced Fischer indole synthesis: A new approach to synthesis of 1,2,3,4-tetrahydrocarbazole and indoles by Amarajothi Dhakshinamoorthy; Kasi Pitchumani (pp. 305-311).

Preparation of 1,2,3,4-tetrahydrocarbazole and substituted indoles, using a solid acid catalyst (namely K-10 montmorillonite clay) via Fischer indole synthesis in methanol medium, is described. The results obtained by the thermal method are compared with those from microwave irradiation. Active participation by adjacent acidic and basic sites of clays is proposed.

Keywords: Fischer indole synthesis; K-10 montmorillonite; 1,2,3,4-Tetrahydrocarbazole; Carbazole; Indole

Direct synthesis of zeolite coatings on cordierite supports by in situ hydrothermal method by Landong Li; Bin Xue; Jixin Chen; Naijia Guan; Fuxiang Zhang; Dexin Liu; Hongqing Feng (pp. 312-321).

A simple and green in situ hydrothermal method, free of organic templates or zeolite seeds, was examined and introduced by depositing several typical microporous aluminosilicate zeolites (Linde A, Linde Y, mordenite and ZSM-5) on cordierite supports. Such preparative factors as crystallization time, crystallization temperature and basic strength were systematically investigated to discuss their effect on the growth of zeolites on cordierite supports. The as-prepared zeolite/cordierite samples were characterized by various techniques and a supposed in situ growth mechanism of zeolites on supports was given. The aluminium atoms on cordierite supports were activated by OH⁻ and these activated atoms subsequently built a zeolite framework together with the silicon atoms and aluminium atoms of the synthesis gel. Based on this, the in situ deposition of zeolites can be easily extended to other aluminium-containing supports. With respect to pure zeolite powders, the in situ coated zeolites on supports exhibited much better stability and accessibility, which were thought essential for industrial applications. Copper ion-exchanged ZSM-5/cordierite was studied as catalyst for the direct decomposition of NO and selective catalytic reduction of NO by propane in excess oxygen. Cu-ZSM-5/cordierite was found to exhibit an obviously enhanced turnover frequency compared to Cu-ZSM-5 powders, which made it a potential deNO_x catalyst for future applications.

Keywords: Zeolite coatings; In situ synthesis; Cordierite; Stability; Accessibility; TOF

Effects of Pd precursors on the catalytic activity and deactivation of silica-supported Pd catalysts in liquid phase hydrogenation by Joongjai Panpranot; Orathai Tangjitwattakorn; Piyasan Praserthdam; James G. Goodwin Jr. (pp. 322-327).

Liquid phase hydrogenation of 1-hexene under mild conditions has been investigated on a series of silica (SiO₂ and MCM-41)-supported Pd catalysts prepared from different Pd precursors such as Pd(NO₃)₂, PdCl₂, and Pd(OOCCH₃)₂. For any silica support, use of PdCl₂ as a precursor resulted in smaller Pd particles, higher dispersion, and consequently higher hydrogenation activities. Supported Pd catalysts prepared from PdCl₂ showed greater metal sintering after 5-h batch reaction. However, leaching of Pd was found to occur to a significant degree for the catalysts prepared from Pd(NO₃)₂ and Pd(OOCCH₃)₂. The results suggest that deactivation of the silica-supported Pd catalysts in liquid phase hydrogenation is dependent on the palladium particle size with smaller Pd particles being more susceptible to sintering while larger particles are more likely to be leached. An optimum Pd particle size may be needed in order to minimize such loss and enhance Pd dispersion.

Keywords: Hydrogenation; Liquid phase hydrogenation; Hexene hydrogenation; Pd/SiO; ₂; Pd/MCM-41; Catalyst deactivation

Rational design of Mg–Al mixed oxide-supported bimetallic catalysts for dry reforming of methane by Andrey I. Tsyganok; Mieko Inaba; Tatsuo Tsunoda; Kunio Uchida; Kunio Suzuki; Katsuomi Takehira; Takashi Hayakawa (pp. 328-343).

A novel synthetic strategy for preparing bimetallic Ru–M (M=Cr, Fe, Co, Ni and Cu) catalysts, supported on Mg–Al mixed oxide, has been introduced. It was based on a “memory effect�?, i.e. on the ability of Mg–Al mixed oxide to reconstruct a layered structure upon rehydration with an aqueous solution. By repeated calcinations–rehydration cycles, layered double hydroxide (LDH) precursors of catalysts containing two different metals were synthesized. Bimetallic catalysts were then generated (i) in situ from LDH under methane reforming reaction conditions and (ii) from mixed metal oxides obtained by preliminary LDH calcination. Among all the LDH-derived catalysts, a Ru^0.1%–Ni^5.0%/MgAlO_x sample revealed the highest activity and selectivity to syngas, a suitable durability and a low coking capacity. A promoting effect of ruthenium on catalytic function of supported nickel was demonstrated. Preliminary LDH calcination was shown to markedly affect the catalytic activity of the derived catalysts and especially their coking properties.

Keywords: Layered double hydroxides; Memory effect; Bimetallic catalysts; Methane; Dry reforming; Synthesis gas

3-Aminopropyltriethoxysilyl functionalized Na-Al-MCM-41 solid base catalyst for selective preparation of 2-phenylpropionitrile from phenylacetonitrile by C. Venkatesan; M. Chidambaram; A.P. Singh (pp. 344-353).

Various solid base catalysts have been prepared by ion exchange of zeolites and Na-Al-MCM-41 and by organosilane grafting over mesoporous materials. Base catalysts thus synthesized were studied in the selective monomethylation of phenylacetonitrile (PAN) to 2-phenylpropionitrile (2-PPN) using dimethylcarbonate (DMC) as an alkylating agent in a Parr autoclave at a temperature ranging between 443 and 473K and at autogenously developed pressure. NH₂-Na-Al-MCM-41 (30) showed a high activity, and the optimum loading of 3-aminopropyltriethoxysilyl (3-APTES) was found to be 1.35mmolg⁻¹, being consistent with the structural characterization. Co-condensation of 3-APTES, tetraethylorthosilicate (TEOS) and sodiumaluminate in the presence of surfactant provides a material with uniformly distributed basic sites responsible for high activity in the selective monomethylation of phenylacetonitrile.

Keywords: Monomethylation; Base catalysis; Phenylacetonitrile; Dimethylcarbonate; 2-Phenylpropionitrile; NH; ₂; -Na-Al-MCM-41

Alkylation of benzene with 1-dodecene in ionic liquids [Rmim]⁺Al₂Cl₆X⁻ (R=butyl, octyl and dodecyl; X=chlorine, bromine and iodine) by Hongliang Xin; Qin Wu; Minghan Han; Dezheng Wang; Yong Jin (pp. 354-361).

Alkylation of benzene with 1-dodecene had been investigated in 1-alkyl-3-methylimidazolium halide-aluminum chloride ionic liquids comprising various alkyl groups (butyl-, octyl- and dodecyl-) and various halogens (chlorine, bromine and iodine) on the cations and anions, respectively. Among all these ionic liquids, [bmim]⁺Al₂Cl₆Br⁻ exhibited the best catalytic performance, which was ascribed to the proper strength of its Lewis acidity and its molecular polarizability demonstrated by FT-IR. The effects of varying anion molar compositions, ionic liquid dosage, reaction temperature, molar ratio of benzene to 1-dodecene and reactant moisture were explored using [bmim]⁺Al₂Cl₆Br⁻ as the catalyst; the results were systematically explained by the mechanism of the carbenium ions. The optimum conversion of 1-dodecene 91.8% with the selectivity to 2-dodecylbenzene 38.0% was obtained when the molar ratio of the ionic liquid [bmim]⁺Al₂Cl₆Br⁻ to 1-dodecene was as low as 0.005 under the mild reaction condition. The reuse of the ionic liquid was examined. The main cause of the deactivation was the loss of the highly Lewis acidic species Al₂Cl₆Br⁻.

Keywords: Alkylation; Ionic liquids; Lewis acidity; Molecular polarizability; FT-IR; Acetonitrile; Carbenium ions

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