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Applied Catalysis A, General (v.304, #1-196)

Editorial Board (pp. co2).

n-Butene skeletal isomerization over HFER zeolites: Influence of Si/Al ratio and of carbonaceous deposits by B. de Ménorval; P. Ayrault; N.S. Gnep; M. Guisnet (pp. 1-13).

The effect of time-on-stream TOS (from 1min to 21.5h) on the rate and selectivity of n-butene transformation at 350°C was determined over a series of HFER zeolites with different Si/Al ratios (6, 9.5, 10, 19 and 32). The porosity and acidity of the fresh and aged samples were characterized by nitrogen adsorption and by NH₃ adsorption at 50°C followed by FTIR, respectively. The main differences between the samples were the following: (i) increase with Si/Al in the activity of the protonic sites (turnover frequency) of fresh samples and in their selectivity for isobutene production, (ii) decrease in the rate of isobutene production with increasing TOS for high Si/Al ferrierites as could be expected from coke formation and complex change for low Si/Al ferrierites with in particular an unexpected increase. Furthermore with all the samples, the turnover frequency for isobutene production increases with TOS whereas the one for propene+pentenes decreases or remains constant. All these observations can be explained by considering the zeolite pore system as a series of non-interconnected nanoreactors (the 10-MR channels) in which the molecules diffuse without any possibility of desorption before their exit while undergoing successive bimolecular reactions. In those with few protonic sites, n-butene isomerizes selectively through an autocatalytic process. In those with many sites a thermodynamic equilibrium mixture of propene, butenes and pentenes is formed.

Keywords: HFER zeolite; Si/Al; Coke; n; -Butene skeletal isomerization; Mechanisms

Methanolysis of styrene oxide catalysed by a highly efficient zirconium-doped mesoporous silica by Davide Barreca; Mark P. Copley; Andrew E. Graham; Justin D. Holmes; Michael A. Morris; Roberta Seraglia; Trevor R. Spalding; Eugenio Tondello (pp. 14-20).

Highly ordered zirconium doped hexagonal mesoporous silicas with Si/Zr ratios of 40:1 and 80:1 have been used as solid acid catalysts for the methanolysis of styrene oxide in a single-mode microwave reactor. The catalysts demonstrated excellent substrate conversion, high product selectivities and were shown to remain highly active for several reaction cycles. The catalyst was regenerated by microwave irradiation in methanol. The effects of concentration of zirconium dopant and reaction time were studied. Products of the reaction were identified by a combination of GC-MS and¹H NMR as 2-methoxy-2-phenylethanol (1), phenyl-acetaldehyde (2), phenylacetaldehyde dimethyl acetal (3) and 1-(1-methoxy-2-(phenethyloxy)ethyl)benzene (4). The relative amounts of these products depended on the zirconium concentration and the reaction time. Thus, with 40:1 Si:Zr catalyst, compounds (1) (93%), (2) (5%) and (3) (2%) were produced after 5min reaction but only (1) (93%) and (3) (7%) were observed after 10min.

Keywords: Mesoporous silica; Zirconium; Styrene oxide; Methanolysis; Regeneration

Study of nickel catalyst in oscillating regime of methane oxidation by means of gravimetry and mass-spectrometry by Victor Yu. Bychkov; Yurij P. Tyulenin; Vladimir N. Korchak; Evgenij L. Aptekar (pp. 21-29).

The application of the thermogravimetric analysis (TGA) combined with on-line mass-spectrometry analysis of the effluent gas mixture from the reactor and temperature programmed reduction (TPR) experiments allowed to obtain information about the content of oxygen and carbon in Ni catalysts during the oscillatory behaviour of methane oxidation. It was demonstrated that the significant variation of the oxygen content (several tens layers) in the Ni catalyst occurred during the oscillatory behaviour of methane oxidation. Together with the visual observation of the color changes due to the periodic variation of the Ni valence these data prove that the oxidation–reduction processes play the crucial role in the origin of the oscillatory behaviour during the methane oxidation over Ni catalysts. It was shown that during oscillatory behaviour of methane oxidation the catalyst contains the significant amount of deposited carbon, atleast, in two different forms. One of them is characterised by the higher reactivity and probably the higher state of the distribution on a metallic surface. The higher activity form of carbon prevails in the reduced state of the nickel catalyst. Another carbon form is characterised by the lower reactivity and, likely, does not noticeably effect the oscillations during methane oxidation.

Keywords: Oscillations; Methane oxidation; Nickel catalysts; Thermogravimetry

Ethanol dehydrogenation over copper catalysts on rice husk ash prepared by ion exchange by Feg-Wen Chang; Hsien-Chang Yang; L. Selva Roselin; Wen-Yao Kuo (pp. 30-39).

Samples of copper on rice husk ash (Cu/RHA) have been prepared by the ion exchange method, with various copper loadings, and have been calcined at different temperatures. Such samples were tested for dehydrogenation of ethanol to acetaldehyde. The samples were characterized by DSC, XRD, FTIR, TEM, XPS, TPR, BET, and H₂–N₂O titration techniques. FTIR spectra illustrate the formation of chrysocolla in uncalcined and calcined Cu/RHA catalyst precursors. DSC, XRD and XPS analyses illustrate that, in Cu/RHA catalyst precursor after drying at 383K, copper is present as Cu(OH)₂ species. After calcination at 723K, copper is present as Cu²⁺ ions and as CuO species. After reduction of the calcined Cu/RHA sample at 523–573K, copper is present as Cu⁺ and/or Cu⁰ species along with unreduced Cu²⁺ species. TEM images show that copper crystallites are spherical in shape and are evenly distributed. TPR results reveal that various copper loadings in calcined Cu/RHA catalyst precursor exhibit similar metal-support interactions (MSI). Ethanol conversion for dehydrogenation of ethanol is found to be independent of calcination temperature and has little effect on Cu loading. Ethanol is selectively converted to acetaldehyde at the reaction temperature of 483–548K. The Cu/RHA catalysts exhibit higher catalytic activity and lower deactivation rate than Cu/SiO₂ catalysts. The activity of Cu/RHA catalysts is found to depend on Cu surface area.

Keywords: Copper catalyst; Rice husk ash; Silica support; Ion exchange; Ethanol dehydrogenation; Acetaldehyde

Influence of solid–acid catalysts on steam reforming and hydrolysis of dimethyl ether for hydrogen production by Kajornsak Faungnawakij; Yohei Tanaka; Naohiro Shimoda; Tetsuya Fukunaga; Shunichiro Kawashima; Ryuji Kikuchi; Koichi Eguchi (pp. 40-48).

Influences of solid–acid catalyst on dimethyl ether steam reforming (DME SR) and DME hydrolysis for hydrogen production were investigated. Series of zeolite (JRC-ZHM20(5), JRC-ZHM90(1) as H-mordenite type and JRC-Z5-90H(1) as ZSM-5 type) and of alumina (ALO8, TA1301, TA3301, DK503, NKHD24, NKHO24 and NK324) were used as acidic catalysts for DME hydrolysis. The composite catalysts of the acidic catalyst and CuFe₂O₄ spinel catalyst were employed for DME SR. DME SR activity strongly depended on the acidic catalyst that is active for DME hydrolysis. The hydrolysis of DME, the rate-determining step in DME SR, is equilibrium-controlled. Zeolite exhibited high activity for DME SR at a low temperature range of 200–275°C, since the hydrolysis could effectively proceed over strong BrØnsted acid-sites approaching its equilibrium. Alumina possessing Lewis acid-sites was active for DME hydrolysis in the higher temperature range from 275 to 450°C. CO₂ and CO with relatively small amounts of CH₄ were found as primary carbon-containing compounds when alumina was used as the acidic catalyst. In the case of zeolite, besides those carbon compounds, C₃H₈, i-C₄H₁₀, and n-C₄H₁₀ were detected during SR and hydrolysis of DME. It was found that not only the acid amount of the acidic catalysts, but also the acid strength and the type of acid-site definitely affected the steam reforming and hydrolysis activity. γ-Alumina (ALO8) mixed with CuFe₂O₄ exhibited the highest DME conversion and hydrogen production with optimum reforming temperature at 350–375°C. Stable activity for DME hydrolysis was attained over ALO8 with high durability for 25h.

Keywords: Dimethyl ether; Alumina; Zeolite; Cu-based spinel; Acidity; Hydrogen; Steam reforming; Hydrolysis

Synthesis of dimethyl ether (DME) on modified HY zeolite and modified HY zeolite-supported Cu–Mn–Zn catalysts by Jinhua Fei; Zhaoyin Hou; Bing Zhu; Hui Lou; Xiaoming Zheng (pp. 49-54).

Synthesis of dimethyl ether (DME) via methanol dehydration were investigated over HY zeolite and over Fe-, Co-, Ni-, Cr-, or Zr-modified HY zeolite, and via direct CO hydrogenation over modified HY zeolite-supported Cu–Mn–Zn catalysts. Zr- and Ni-modified HY zeolite exhibited higher activity and stability for methanol dehydration, while Fe-, Co-, and Cr-modified HY zeolite deactivated quickly due to carbon deposition. For DME synthesis directly from CO hydrogenation, it was found that the amount of dehydration component had an important influence on the performance of the dual catalyst. Zr–HY supported Cu–Mn–Zn catalyst was more active and stable than Cu–Mn–Zn/HY in the “synthesis gas to dimethyl ether�? process.

Keywords: Dimethyl ether; Methanol; Zeolite HY; Cu–Mn–Zn catalyst

Photocatalytic degradation of organic contaminants in water by ZnO nanoparticles: Revisited by C. Hariharan (pp. 55-61).

Nanoscale photocatalysts have attracted much attention due to their high surface area to volume ratios. This work investigates the photodegradation of organic contaminants using the fluorescence emission characteristics of ZnO nanoparticles (ZnO-nano) in aqueous solutions. This is accomplished by preparing nanocrystalline ZnO; the presence of organic contaminants in water is readily detected from the quenching of fluorescence observed from ZnO semiconductor films. Photolysis of ZnO thin films immersed into an aqueous system containing organic contaminants results in the degradation of the contaminants. A comprehensive study has been done involving several organic contaminants in water (like aliphatic and aromatic chloro compounds as well as some commonly used aromatic solvents) to check the suitability of ZnO-nano as an efficient photocatalyst. The ZnO nanoparticles not only serve as a better catalytic system compared to bulk ZnO and commercially available Degussa TiO₂ in achieving degradation of the added contaminants, but unlike other semiconductor systems can also act as a non-specific sensor for the presence of these common contaminants in water. A total cleanup of a cocktail of contaminants in water was also achieved using the ZnO-nano.

Keywords: ZnO; Nanoparticles; Semiconductor; Organic contaminants and photocatalysis

Temperature profile of catalyst bed during oxidative steam reforming of methane over Pt-Ni bimetallic catalysts by Baitao Li; Shigeru Kado; Yuya Mukainakano; Mohammad Nurunnabi; Toshihiro Miyao; Shuichi Naito; Kimio Kunimori; Keiichi Tomishige (pp. 62-71).

The catalyst bed temperature during oxidative reforming of methane (CH₄/H₂O/O₂/Ar=40/30/20/10) at 1123K and atmospheric pressure was investigated by infrared thermography over γ-Al₂O₃ supported bimetallic Pt-Ni catalysts prepared by different impregnation methods: co-impregnation and sequential impregnation. The thermographical results clearly demonstrated that the catalyst bed temperature was strongly dependent on the preparation method. The bimetallic catalyst prepared from the sequential impregnation method exhibited much higher resistance to hot spot formation in oxidative reforming of methane. Temperature programmed reduction (TPR) with H₂ revealed that the addition of Pt by a sequential impregnation method greatly promoted the reduction of Ni species; furthermore, infrared spectra of CO adsorption suggests that the surface composition of Pt on the catalyst prepared by the sequential method is much higher than that for the catalyst prepared by the co-impregnation method. The surface enrichment of Pt is responsible for the effective overlap between the combustion and reforming zones, and this can enhance the inhibition of hot spot formation.

Keywords: Oxidative steam reforming of methane; Pt; Ni; Bimetallic catalyst; Thermograph; Hot spot

Vapor-phase oxidative carbonylation of ethanol over CuCl–PdCl₂/C catalyst by Tuan-Chi Liu; Chung-Shin Chang (pp. 72-77).

CuCl–PdCl₂/C catalysts were prepared, characterized, and used for the synthesis of diethyl carbonate. Conventional impregnation was adopted for the preparation of the catalyst. Water-insoluble cuprous chloride, CuCl, was dissolved in hydrochloric acid. Catalytic properties were characterized by XRD, XPS and TPD. The activities of the catalysts in the oxidative carbonylation of ethanol were measured using a continuous flow micro-reactor. The results revealed that CuCl–PdCl₂/C catalyst was not only active but also very selective for the production of diethyl carbonate. The selectivity was 100% at a reaction temperature below 120°C. However, despite all its merits, the catalyst was easily deactivated in the reaction. The main causes of the deactivation were the sintering of the cuprous chloride and the decomposition of the palladium chloride.

Keywords: Diethyl carbonate; Cuprous chloride catalyst; Oxidative carbonylation, Palladium chloride

The water-gas-shift reaction over Ir/TiO₂ and Ir–Re/TiO₂ catalysts by Yasushi Sato; Yoshinori Soma; Toshihiro Miyao; Shuichi Naito (pp. 78-85).

Water-gas-shift reactions over Ir/TiO₂ and Ir–Re/TiO₂ catalysts were studied, employing a closed gas circulation system. Addition of Re to Ir/TiO₂ catalysts clearly accelerated the WGS reaction, as is in the cases of our previous study over Pt/TiO₂ and Pd/TiO₂ catalysts. The FT-IR analyses of the adsorbed species during the reaction exhibited the enhancement of the adsorbed CO peaks in the lower wavenumber region with the increase of Re content. These peaks are supposed to be the adsorbed CO neighboring to the adsorbed OH function, which was formed by the dissociation of water on the Re metal or ReO_x species of Ir–Re/TiO₂ catalysts.

Keywords: Ir/TiO; ₂; catalyst; Ir–Re/TiO; ₂; catalyst; Water-gas-shift reaction; FT-IR

Kinetic considerations of H₂ assisted hydrocarbon selective catalytic reduction of NO over Ag/Al₂O₃ by Henrik Backman; Kalle Arve; Fredrik Klingstedt; Dmitry Yu. Murzin (pp. 86-92).

A kinetic study of the reduction of NO by n-octane performed isothermally (200°C) at steady state conditions over an active Ag/alumina catalyst was carried out in the presence of hydrogen. The mathematical model was based on a supposed reaction mechanism, which among other steps includes molecular adsorption of NO and CO as well as dissociative adsorption of H₂ and O₂. Formation of CO₂ is assumed to go through oxidation of CO. A comparison between experimental data and simulations revealed that the developed mathematical model is able to describe the observed reduction of NO in presence of H₂ sufficiently well.

Keywords: HC-SCR; Hydrogen effect; Silver; Kinetic modelling

Oxygen adsorption on silver catalysts during the course of partial oxidation of ethylene by Akimi Ayame; Shigeru Eimaeda; Lin Feng; Hirofumi Hayasaka (pp. 93-108).

To explore oxygen adsorption kinetics on silver catalyst surfaces during the course of ethylene oxidation, relations between the amount of oxygen consumed by reaction with ethylene ( q) and oxygen partial pressure (pO2) at a given ethylene pressure (pC2H4), i.e., kinetic data, were measured using a pulse reaction technique on K₂SO₄-promoted Ag/α-Al₂O₃ catalyst and a flow reaction method on Cs and Re-copromoted Ag/(α-Al₂O₃-crystal) catalyst at 453–529K. The kinetic data were analyzed by the use of three kinetic models derived on the basis of a redox model assuming that, under steady states, no oxygen desorption occurred and the rate of oxygen adsorption on silver surface was equal to the rate of surface reactions consisting of adsorbed oxygens and gaseous ethylene. One was the model that two-step consecutively dissociative oxygen adsorptions forming oxygen adatom and then admolecule were rate-determining (Model 1), and others were molecular oxygen adsorption rate-determining model (Model 2) and surface reaction rate-determining model when one-step dissociative oxygen adsorption forming oxygen adatom only lay in a complete equilibrium state (Model 3). The Model 1 showed the most excellent suitability to the kinetic data and reproduced accurately the distinctive features for experimentalq–pO2 curves. The coverage of oxygen admolecule estimated from the Model 1 was 0.48–0.96 and 0.12–0.34 on the K₂SO₄-promoted Ag/α-Al₂O₃ catalyst atpC2H4≦0.03 atom and on the Cs and Re-copromoted Ag/(α-Al₂O₃-crystal) catalyst atpC2H4≧0.30 atom, respectively. They were about thousand times bigger than those for oxygen adatom. These results indicated that the first dissociative adsorption on vacant active center was much slower than the second dissociative oxygen adsorption on adatom; the adatom seemed likely to act as active center for the second oxygen adsorption. Selectivity to ethylene oxide elevated almost linearly with increase in the coverage of oxygen admolecule. Activation energies and heats of adsorption obtained for dissociative oxygen adsorption were quite reasonable values compared to literature values and remarkedly reduced with increasingpC2H4.

Keywords: Silver catalyst; Ethylene; Partial oxidation; Dissociative oxygen adsorption; Superoxide; Redox model; Adsorption kinetics

Spillover hydrogen mobility during Co–Mo catalyzed HDS in industrial-like conditions by P. Baeza; M. Villarroel; P. �?vila; A. López Agudo; B. Delmon; F.J. Gil-Llambías (pp. 109-115).

The work concerns the spillover hydrogen (H_so) mobility between Co₉S₈ and MoS₂ and the corresponding synergetic effects in gas–oil hydrodesulfurization (HDS), when a solid material separates the partners, either as a powder or a monolith surface. The influences of the distance (0–10mm) between Co₉S₈ and MoS₂ and the nature of the separator (γ-Al₂O₃, SiO₂, carbon, MgSiO₃ and two silica–aluminas) on the synergism were studied. A correlation exists between the value of the isoelectric point (IEP) of the separator surface and the enhancement of HDS activity. Inferring that the synergetic effect is due to hydrogen spillover, this shows that the IEP is an important parameter controlling spillover. To our knowledge, this is the first time the IEP of surfaces has been shown to have a direct effect on the spillover of hydrogen. The other results confirm that the remote control model is able to explain the synergism detected in this study.

Keywords: Hydrodesulfurization; Spillover hydrogen; CoS; _x; and MoS; ₂; phases; Industrial-like conditions; Remote control; Composite bed; Monolith support

Hydrogen production by ethanol reforming over NiZnAl catalysts by M. Noelia Barroso; Manuel F. Gomez; Luis A. Arrúa; M. Cristina Abello (pp. 116-123).

NiZnAl catalysts with different Ni loading (1–25wt.%) and a Zn:Al atomic ratio nearly constant (Zn:Al≅0.6) were prepared by the citrate sol gel method and characterized by different techniques such as TG, BET, TPR, XRD and FT-IR. They were active in the ethanol steam reforming at atmospheric pressure in the temperature range 500–600°C. However, there were significant differences in their performance. On catalysts with high Ni loading (18–25wt.%) high hydrogen selectivities around 85% were obtained. CO, CO₂ and small amount of CH₄ were the only by-products at 600°C.

Keywords: Ethanol; Steam reforming; Hydrogen production; NiZnAl catalysts

Synthesis of Ni–Mo–W sulphide catalysts by ex situ decomposition of trimetallic precursors by R. Huirache-Acuña; M.A. Albiter; J. Espino; C. Ornelas; G. Alonso-Nuñez; F. Paraguay-Delgado; J.L. Rico; R. Martínez-Sánchez (pp. 124-130).

Nickel–molybdenum–tungsten sulphide unsupported catalysts were prepared by ex situ decomposition of trimetallic (Ni–Mo–W) precursors. The precursors were synthesized by impregnation of ammonium or tetraalkylammonium thiomolybdates on tungsten thiosalts (ammonium or tetraalkylammonium thiotungstates). Finally, the bimetallic precursors (Mo–W) were impregnated with Ni(NO₃)₂·6H₂O previously dissolved in water in order to give a final molar ratio Ni:Mo:W of 2:1:1. By the ex situ decomposition (activation), the precursors were transformed under a flow of H₂S (15%) in hydrogen from room temperature to 673K at 4K/min, dwell of 4h at 673K. All catalysts were tested in the hydrodesulphurization (HDS) of dibenzothiophene (DBT) and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM). Furthermore, the specific surface areas were measured using the BET method. The catalysts obtained present low specific surface areas, poorly crystalline structures with cavities and disordered structure and different catalytic activities in the HDS of DBT. The best HDS catalytic activity was shown by the sample labeled as NiMoW–H ( k=13.4×10⁻⁷mol/g^*s).

Keywords: Unsupported catalysts; Ex-situ decomposition; Impregnation; Hydrodesulphurization

Production of alkylated gasoline using ionic liquids and immobilized ionic liquids by Prashant Kumar; Walter Vermeiren; Jean-Pierre Dath; Wolfgang F. Hoelderich (pp. 131-141).

Ionic liquids (ILs) and immobilized ionic liquids were used as acid catalysts for the liquid phase alkylation of raffinate II and isobutane. The influences of reactant concentration (molar ratio of iC₄/C^₄), time, temperature and acid strength of the ionic liquids were studied. Using a step-up design under batch conditions with a very dilute mixture of isobutane and alkene, the conversion for a variety of ionic liquids was found to follow a pattern based on acid strength of the catalyst. Imidazolium based ILs were found to be superior to phosphonium based ILs. Novel Lewis-Acid Catalysts II (NLAC II, immobilization by grafting on siliceous MCM 41 or on silica FK 700) are better than other solid acid catalysts tested, such as SAC 13, zeolite H-Beta (Si/Al=14) and NLAC I (impregnation of ILs on silica FK 700). Possible leaching of the ionic liquid from the catalyst surface was followed by ICP measurements of the catalyst after reaction and of the reaction mixture.

Keywords: Alkylated gasoline; Raffinate II; Ionic liquid; Immobilized ionic liquids; Isobutane alkylation; Hydride transfer

Influence of reaction temperature and crystallite size on HBEA zeolite deactivation by coke by Patrick Magnoux; Andry Rabeharitsara; Henrique S. Cerqueira (pp. 142-151).

The deactivation by coke of a HBEA zeolite (Si/Al=15 crystal size=0.02μm) was investigated using the methylcyclohexane (mcha) model reaction at different temperatures and several contact times. At 350 and 450°C, C₂–C₇ olefins and paraffins (cracking products), dimethylcyclopentanes and ethylcyclopentane (isomers), aromatics (benzene, toluene, xylenes) and coke were formed. At 250°C and at low contact time, only isomers were formed whereas, at high contact time, due to the presence of strong acid sites on the zeolite, cracking products and coke were formed. At all temperatures, cracking products consist only of paraffins showing that hydrogen transfer occurs. Coke was formed through successive reactions of olefins and was mainly constituted of methylnaphthalene.At 350°C on HBEA which has similar acidity but larger crystal size (10μm), deactivation and coke formation were enhanced. Furthermore, the lower diffusivity of reaction products (olefins and aromatics) leads to the formation of polyaromatic compounds non-detected with the HBEA(15) zeolite which present small crystal size (0.02μm).

Keywords: Zeolite deactivation; Coke formation; BEA zeolite; Crystallite size; Methylcyclohexane

Transesterification of dimethyl carbonate with diethyl carbonate over Al-Zn-MCM-41 and Al-MCM-41 molecular sieves by Arudra Palani; Narasiman Gokulakrishnan; Muthaiah Palanichamy; Arumugam Pandurangan (pp. 152-158).

Al-MCM-41 (Si/Al=50, 100) and Al-Zn-MCM-41 (Si/Al+Zn=50, 100) were synthesised hydrothermally and characterised by XRD, BET, TPD-Pyridine, FT-IR and²⁷Al MAS-NMR techniques. Their catalytic activity was tested for the transesterification of dimethyl carbonate (DMC) with diethyl carbonate (DEC). The reaction was carried out at 125, 150, 175 and 200°C with feed ratio 1:1. Al-Zn-MCM-41 (50) was found to be more active than other catalysts. The DMC conversion was maximum at 175°C. The study of time-on-stream showed decrease of conversion with increase in stream. The activity of the catalysts followed the order Al-Zn-MCM-41 (50)>Al-Zn-MCM-41 (100)>Al-MCM-41 (50)>Al-MCM-41 (100), which is also the order of the acidity of the catalysts.

Keywords: Ethyl methyl carbonate; Diethyl carbonate; Dimethyl carbonate; Transesterification; Al-MCM-41; Al-Zn-MCM-41

Effect of the presence of chlorine in bimetallic PtZn/CeO₂ catalysts for the vapor-phase hydrogenation of crotonaldehyde by Joaquín Silvestre-Albero; Fernando Coloma; Antonio Sepúlveda-Escribano; Francisco Rodríguez-Reinoso (pp. 159-167).

The effect of the reduction temperature has been studied on ceria-supported bimetallic platinum–zinc catalysts prepared from H₂PtCl₆ and Pt(NH₃)₄(NO₃)₂ as the platinum precursors and Zn(NO₃)₂ as the zinc precursor. The catalysts have been characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS), and their catalytic behavior has been evaluated in the vapor-phase hydrogenation of toluene and of crotonaldehyde (2-butenal) after reduction at low (473K) and high (773K) temperatures. The increase in the reduction temperature produces a strong decrease in the catalytic activity for toluene hydrogenation in both systems, but an important increase of activity for crotonaldehyde hydrogenation, which is more evident for the chlorine-free catalyst. The selectivity towards the hydrogenation of the carbonyl bond to yield the unsaturated alcohol (crotyl alcohol, 2-buten-1-ol) also increases after reduction at high temperature, being somewhat higher for the Cl-containing catalyst. The results are discussed in terms of differences in surface composition of the catalysts.

Keywords: PtZn/CeO; ₂; Selective hydrogenation; XPS; Chlorine effect

The synthesis of acetic acid from methane via oxidative bromination, carbonylation, and hydrolysis by K.X. Wang; H.F. Xu; W.S. Li; C.T. Au; X.P. Zhou (pp. 168-177).

Acetyl bromide and acetic acid (AA) were synthesized from methane by an energy-saving process. By reacting methane with oxygen in the presence of HBr and H₂O over a 2.5% Ba 2.5% La 0.5% Ni 0.1% Ru/SiO₂ catalyst, methane was converted to CH₃Br and CO (CH₃Br/CO molar ratio=1/1) with a CH₄ single-pass conversion of 70% at 660°C. Our results showed that CH₃Br was formed via the interaction of methane with bromine radicals whereas CO was generated in the oxidation of CH₃Br. Through the carbonylation of CH₃Br over RhCl₃-KI or RhCl₃-PPh₃ (triphenyl phosphine) catalyst in propanoic acid, acetyl bromide could be synthesized and readily hydrolysed to acetic acid at room temperature (with more than 99.7% yield based on CH₃Br). The promotional action of PPh₃ and KI is realized via the direct coordination of PPh₃ to Rh and the conversion of CH₃Br to CH₃I by means of Br–I exchange, respectively.

Keywords: Methane oxidative bromination; Carbonylation; Acetic acid synthesis; Carbonylation catalyst

Catalytic oxidation of cyclohexane to cyclohexanone and cyclohexanol by oxygen in a solvent-free system over metal-containing ZSM-5 catalysts by H.-X. Yuan; Q.-H. Xia; H.-J. Zhan; X.-H. Lu; K.-X. Su (pp. 178-184).

Heterogeneous oxidation of liquid cyclohexane by molecular oxygen was carried out over metal-containing ZSM-5 catalysts in a solvent-free system. Among those M-ZSM-5 and M/ZSM-5 catalysts tested, Co-containing ZSM-5 catalysts including Co/ZSM-5 (prepared by ion-exchange and calcination) and Co-ZSM-5 (prepared by ion-exchange and drying) showed the best activity for the oxidation of cyclohexane to cyclohexanone and cyclohexanol. Co/ZSM-5 had almost the same activity as Co-ZSM-5 for the cyclohexane oxidation; however, the leaching of cobalt from Co-ZSM-5 readily occurred. Co/ZSM-5 (calcined) catalyst could achieve about 10mol% conversion of cyclohexane and 97% selectivity of KA-oil (the mixture of cyclohexanone and cyclohexanol) at 393K under the pressure of 1.0MPa O₂. In addition, other factors like the temperature, the pressure, the time, various metals, the tert-butylhydroperoxide (TBHP) addition, and the catalyst reuse were investigated carefully. For the titled oxidation, Co/ZSM-5 was recyclable, and could behave as a truly heterogeneous catalyst.

Keywords: Metal-containing ZSM-5; Cyclohexane oxidation; Molecular oxygen; Solvent-free system

Oxyfunctionalization of n-pentane and n-hexane by oxovanadium complexes supported on carbamated modified silica gel by Gopal S. Mishra; Armando J.L. Pombeiro (pp. 185-194).

The bis(maltolato)oxovanadium complexes cis-[VO(OCH₃)(ma)₂]1, cis-[VO(OC₂H₅)(ma)₂]2, [VO(ma)₂]3 and [VO(py)(ma)₂]4 have been anchored to chemically modified silica gel and are shown to act as supported catalysts for the oxidation of n-pentane and n-hexane, with molecular oxygen under relatively mild reaction conditions, to the corresponding ketones (with good selectivities) and alcohols (in smaller amounts). cis-[VO(OCH₃)(ma)₂]1 provides the best results in both cases and the effects of various factors (temperature, time, O₂ pressure, catalyst amount) were also investigated towards the optimization of the reaction conditions. 2-pentanone (84% selectivity) and a small amount of 2-pentanol are formed from n-pentane at 150°C, p(O₂)=15atm, while 2-hexanone (58% selectivity), 1-hexanol and acetic acid are obtained from n-hexane at 160°C, p(O₂)=10atm. The involvement of a carbon- and oxygen-centred radical mechanism is suggested by experiments with free radical traps. Heteroaromatic acids were tested as possible co-catalysts and 2-pyrazinecarboxylic acid was the most effective one. Thermogravimetric analysis (TGA) indicates the catalyst is stable up to ca. 220°C and inductive couple plasma (ICP) shows a notable extensive vanadium loss from the supported catalyst after the reaction, allowing further use of the catalyst even without reactivation.

Keywords: Vanadium–maltolato complexes; Carbamated silica gel; n; -pentane; n; -hexane; Molecular oxygen; Heteroaromatic acids; Mechanism

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Applied Catalysis A, General (v.304, #1-196)