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Applied Catalysis A, General (v.356, #1)

Contents (pp. iii-vi).

Editorial Board (pp. co2).

Recent developments in catalysis using nanostructured materials by N. Raveendran Shiju; Vadim V. Guliants (pp. 1-17).

This review describes recent developments of size-, shape-, structure- and composition-dependent behavior of catalyst nanoparticles employed in alkylation, dehydrogenation, hydrogenation, and selective oxidation reactions for the conversion of hydrocarbons (with main emphasis on fossil resources) to chemicals. Innovation in these areas is largely driven by novel synthesis of (nano)porous and nanostructured catalytic materials. In case of alkylation, several new classes of porous materials have recently emerged as catalysts while the discovery of novel ultralarge-pore frameworks with desirable acidity remains largely a serendipitous process. Noble metal nanoparticles such as Pt, Pd, Rh, Au and their alloys with other metals have been extensively employed to catalyze a wide range of dehydrogenation, hydrogenation, and selective oxidation reactions of organic molecules. Novel approaches are still required to synthesize and characterize stable gold and other metal nanoparticles with tightly controlled sizes to further advance the knowledge of their unique size-dependent catalytic behavior. The bulk mixed metal oxides of vanadium, molybdenum, and other transition metals, such as the M1 phase for propane ammoxidation to acrylonitrile, have shown great promise as highly active and selective oxidation catalysts. However, fundamental understanding of surface molecular structure–reactivity relationships of these systems remains highly limited. Future advances in all these areas may be possible through combined experimental and theoretical approaches.This review highlights the current global status and emerging trends in chemical catalysis employing nanostructured catalysts. The recent developments of size-, shape-, structure- and composition-dependent behavior of catalyst nanoparticles employed in alkylation, dehydrogenation, hydrogenation, and selective oxidation reactions for the conversion of hydrocarbon resources to chemicals as well as the future trends are discussed.

Keywords: Heterogeneous catalysis; Nanostructured materials; Alkylation; Dehydrogenation; Hydrogenation; Selective oxidation

Correlating NEXAFS characterization of Co–W and Ni–W bimetallic carbide catalysts with reactivity for dry reforming of methane by Huifang Shao; Edwin L. Kugler; Dady B. Dadyburjor; Sergey A. Rykov; Jingguang G. Chen (pp. 18-22).

The effect of temperature on the structure and performance of Co–W–C and Ni–W–C catalysts for dry reforming of methane (DRM) has been investigated using both reactors and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. For Co–W–C, the DRM reactivity is greatly improved after being exposed to methane at 850°C. For Ni–W–C, however, the catalytic performance before such exposure is good, although no obvious difference has been found in the catalytic performance before and after exposure to methane at 850°C. In this work, NEXAFS has been applied to characterize the fresh and spent catalysts, both before and after exposure to the reactants at 850°C, for both Co–W–C and Ni–W–C. Three NEXAFS regions have been investigated for each catalyst: the carbon K-edge, the oxygen K-edge and the L-edge of either cobalt or nickel. NEXAFS results provide insights into the possible origins for the different performance of those two different carbides. To exhibit reasonable reactivity for DRM, Ni–W oxide and Co–W oxide are required to be reduced, and the active stable catalysts must contain large amounts of carbon so that WC and either Ni or Co are seen in the bulk. NEXAFS results indicate that Ni–W–C can be reduced to a greater extent and at a lower temperature than Co–W–C. In addition, NEXAFS measurements reveal the formation of graphitic carbon at or near the surface region. This species can play a critical role in the reactivity and stability of the catalysts for DRM.The effect of temperature on the structure and performance of Co–W–C and Ni–W–C catalysts for dry reforming of methane has been investigated using both reactors and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Ni–W–C is reduced more than Co–W–C. Graphitic carbon formed at or near the surface region plays a critical role in the reactivity and stability of the catalysts.

Keywords: Bimetallic carbide; Dry reforming; Methane; NEXAFS

Assessing the acid properties of desilicated ZSM-5 by FTIR using CO and 2,4,6-trimethylpyridine (collidine) as molecular probes by Martin Spangsberg Holm; Stian Svelle; Finn Joensen; Pablo Beato; Claus Hviid Christensen; Silvia Bordiga; Morten Bjørgen (pp. 23-30).

This FTIR study shows that zeolite defects (internal Si-OH sites) are removed upon NaOH treatment. Free Si-OH sites in the mesopores increase in concentration. Some mesopores are protected by the microporous framework. Mesopore formation appears to take place at defective sites. The acid strength of Brønsted sites is unaffected, but Lewis acidity on the external crystal surface is formed.A series of desilicated ZSM-5 catalysts previously shown to have improved catalytic performance in the MTG (methanol-to-gasoline) reaction [M. Bjørgen, F. Joensen, M.S. Holm, U. Olsbye, K.-P. Lillerud, S. Svelle, Appl. Catal. A 345 (2008) 43] was subjected to thorough examination using FTIR. Clearly, defects represented by internal Si-OH sites are removed upon NaOH treatment. In a parallel manner, free Si-OH sites increase in concentration and the results point to a selective mechanism for formation of mesopores as the framework dissolution preferentially takes place at defective sites in the crystallites. The acid properties of the desilicated materials were investigated by applying CO and collidine (2,4,6-trimethylpyridine) as molecular probes. Monitoring the induced frequency shifts upon CO adsorption at liquid N₂ temperature revealed that the desilication procedure did not alter the acid strength of the Brønsted sites significantly. This weakens the explanation linking improved catalytic behaviour, such as increase in both catalyst activity and hydrogen transfer activity, to modified Brønsted acid strength. Simultaneous to the mesopore formation resulting from the desilication, strong Lewis acid sites were generated, presumably from dislodged framework aluminium. Collidine, which is too bulky to enter the micropore system of ZSM-5, could access Lewis acidity, suggesting that these sites were predominantly generated on the external surface or in the newly created mesopores. Additionally, by first saturating the zeolite surface with collidine and subsequently adsorbing CO, we show that barely any Lewis acidity was uncoordinated post-collidine saturation while the Brønsted acidity continuously was protected behind the micropore system. It is hypothesized from the present study that the desilication procedure can lead to a slight dealumination of the samples while forming Lewis acidity preferentially at the crystal surface.

Keywords: MFI; MTG; MTH; NaOH treatment; Mesoporous; Lewis acidity

Quantitative determination of sites able to chemisorb CO on Au/ZrO₂ catalysts by F. Menegazzo; F. Pinna; M. Signoretto; V. Trevisan; F. Boccuzzi; A. Chiorino; M. Manzoli (pp. 31-35).

Quantitative volumetric measurements of low temperature CO chemisorption on Au/ZrO₂ catalysts and Fourier transform infrared measurements of adsorbed CO in well defined and controlled conditions of temperature and pressure are here presented as widely accessible and reproducible methods for determining the concentration of gold sites able to chemisorb CO on Au/ZrO₂ catalysts. HRTEM analyses were also performed in order to support the validity of the measurements.

Keywords: CO; Volumetric chemisorption; IR CO absorption; Au/ZrO; ₂; Gold active sites

Complete oxidation of isopropanol over Cu₄O₃ (paramelaconite) coating deposited on fiberglass by CVD by Jorge Medina-Valtierra; Claudio Frausto-Reyes; Gabriela Camarillo-Martínez; Jorge A. Ramírez-Ortiz (pp. 36-42).

Thin films of paramelaconite, tenorite and their mixtures were deposited on fiberglass substrate by chemical vapor deposition and catalytically evaluated by isopropanol oxidation at low temperatures between 150 and 275°C. Copper oxides were deposited using bis(2,4-pentanedionato)copper(II) as a precursor and oxygen as carrier-reactant gas. Original crystalline phases deposited on fiberglass at different temperatures or formed subsequently were characterized by several analytical techniques. Films gave crystallite sizes from 6.5 to 8.4nm and a thickness around 230nm. The fiberglass with a paramelaconite film showed a relatively high catalytic activity, more than 40%, at 250°C. Nevertheless, the fiberglass with a tenorite film exhibited a catalytic activity of only 10% at the same temperature. Above 250°C the paramelaconite experienced a notable deactivation after which the catalytic activity decreased to 6.7% at 350°C and after this, the catalyst could not be reused. This activity loss was probably due to changes in the chemical phases on fiberglass by effect of temperatures above 250°C.Films of paramelaconite were deposited on fiberglass by CVD and evaluated by isopropanol oxidation at low temperatures. Films gave crystallite sizes from 6.5 to 8.4nm and a thickness around 230nm. Paramelaconite films showed a catalytic activity of 42% at 250°C. Nevertheless, above this temperature the paramelaconite experienced a notable deactivation. This activity loss was due to changes in the chemical phases of copper by effect of higher temperatures.

Keywords: Paramelaconite film; CVD process; Catalytic fibers; Characterization study; Isopropanol oxidation

Selectivity enhancement in the catalytic hydrogenation of propionitrile using ionic liquid multiphase reaction systems by Katharina Obert; Daniel Roth; Martin Ehrig; Andreas Schönweiz; Daniel Assenbaum; Harald Lange; Peter Wasserscheid (pp. 43-51).

An approach to improve the primary amine selectivity in nitrile hydrogenation is presented. The new concept was carried out in a multiphase system comprising two liquid phases, namely an ionic liquid and an organic solvent. The new concepts led to an increase in propylamine selectivity from approx. 50% in the IL-free reference system up to 85% in the IL system.A new ionic liquid based, multiphase reaction system was investigated for the catalytic hydrogenation of propionitrile. The reaction system under investigation consisted of a solid heterogeneous Ru-catalyst (Ru on carbon), two liquid phases and the hydrogen gas-phase. By using two liquid phases in the reactor – of which one was an ionic liquid – it was possible to improve significantly the selectivity for the formation of propylamine by suppressing consecutive reactions to dipropylamine and tripropylamine. This enhanced selectivity resulted either from the protonation of the primary formed amine (in case of the Brønsted acidic ionic liquids dimethylcyclohexylammonium hydrogensulfate and 1-butylimidazolium hydrogensulfate) or from the extraction of the primary amine into the organic phase (in case of a 1-ethyl-3-methylimidazolium ethylsulfate/1,2,4-trichlorobenzene biphasic system).

Keywords: Propylamine; Hydrogenation; Ionic liquid; Biphasic

Skeletal isomerization of unsaturated fatty acids on Beta zeolites: Effects of calcination temperature and additives by Long Ha; Jingbo Mao; Jinxia Zhou; Z. Conrad Zhang; Shuguang Zhang (pp. 52-56).

A commercial Beta zeolite calcined at about 450°C generated catalysts with high activities for the skeletal isomerization of oleic acid. Addition of a small amount of water to the fatty acid promoted the conversion. The poisoning effect of the carboxylic group of oleic acid was demonstrated by the comparison of the isomerization reactions of oleic acid and 1-octadecene.▪A commercial Beta-type zeolite was studied for upgrading unsaturated fatty acids, a renewable feedstock. Catalyst calcination and additive addition were investigated aiming to improve the catalytic activity for the skeletal isomerization of oleic acid. Calcination at a temperature around 450°C instead of the commonly used 550°C generated catalysts with relatively low surface areas but high activities, which is attributed to the high Brønsted acidity as revealed by FTIR characterization. Addition of a small amount of water (2–5wt% of fatty acid) to the fatty acid promoted the conversion, but any further increase in the amount of water would result in a catalytic activity loss. Although methanol did not show a promoting effect for the isomerization, the methyl ester of oleic acid showed a higher conversion than oleic acid on the same catalyst. The poisoning effect of the carboxylic group on oleic acid was demonstrated by the comparison of the isomerization reactions of oleic acid and 1-octadecene.

Keywords: Isomerization; Fatty acid; Beta zeolite; Catalyst

Basic properties of rare earth oxides by Satoshi Sato; Ryoji Takahashi; Mika Kobune; Hiroshi Gotoh (pp. 57-63).

Basic properties of rare earth oxides were measured by CO₂ desorption. The crystal structure varies with the ionic radius and with the valence of rare earth metals. The basic strengths of rare earth oxides are attributed to lanthanide contraction: the strength of the basic sites decreases with decreasing radius of the rare earth cation.Basic properties of rare earth oxides (REOs) calcined at different temperatures were investigated. During the calcination process, the crystal structures of Lu, Yb, Tm, Er, Y, Ho, and Dy oxides transformed from monoclinic to cubic with increasing calcination temperature, while those of Sc, Ce, La, Pr, Nd, Sm, Eu, Gd, and Tb oxides showed no change at temperatures below 1100°C. No acidic sites were observed in the measurement of NH₃ adsorbed on the REOs at 25°C. CO₂ was adsorbed on the REOs: CO₂ desorption peaks were observed depending on the strength of the basic sites. Light REOs, such as La₂O₃, Pr₆O₁₁, Nd₂O₃, and Sm₂O₃, had surface basic sites from which CO₂ desorbed at temperatures below 500°C, as well as structural carbonate that decomposed above 500°C. Heavy REOs, such as Dy₂O₃, Ho₂O₃, Y₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, and Lu₂O₃, had weak basic sites. The basic properties of REOs are attributed to lanthanide contraction: the strength of the basic sites decreases with decreasing radius of the rare earth cation.

Keywords: Rare earth oxide; Phase transition; Basic property; Lanthanide contraction

Dehydration of 1,4-butanediol over rare earth oxides by Satoshi Sato; Ryoji Takahashi; Mika Kobune; Hirotomo Inoue; Yusuke Izawa; Hironobu Ohno; Kazunari Takahashi (pp. 64-71).

Vapor-phase catalytic dehydration of 1,4-butanediol was investigated over rare earth oxides (REOs) calcined at different temperatures. In the dehydration of 1,4-butanediol over the REOs, 3-buten-1-ol was dominantly produced, together with the formation of tetrahydrofuran. Weakly basic heavy REOs, such as Er₂O₃, Yb₂O₃, and Lu₂O₃, calcined at 1000°C with C-type bixbyite structure showed high formation rates of 3-buten-1-ol.Vapor-phase catalytic dehydration of 1,4-butanediol was investigated over rare earth oxides (REOs) calcined at different temperatures. In the dehydration of 1,4-butanediol over REOs, 3-buten-1-ol was mainly produced, together with tetrahydrofuran (THF). Weakly basic heavy REOs, such as Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, Lu₂O₃, and Y₂O₃, showed high selectivity to 3-buten-1-ol, while strongly basic light REOs, such as La₂O₃, Pr₆O₁₁, Nd₂O₃, Sm₂O₃, and Eu₂O₃, produced more THF and γ-butyrolactone. Heavy REOs exhibited different catalytic activities in the dehydration of 1,4-butanediol depending on their crystal structures. Cubic C-type REOs selectively produced 3-buten-1-ol; in particular, cubic Er₂O₃, Yb₂O₃, and Lu₂O₃ showed the highest formation rates of 3-buten-1-ol. Since the formation rate of 3-buten-1-ol was suppressed over Er₂O₃ in acidic CO₂ or basic NH₃ carrier gas flow, it is probable that the active centers for the formation of 3-buten-1-ol are composed of both basic and acidic sites.

Keywords: Homoallyl alcohol; 3-Buten-1-ol; 1,4-Butanediol; Dehydration; Rare earth oxide

Preparation of porous ruthenium catalysts utilizing a silsesquioxane ligand; catalytic activity towards hydroformylation of 1-octene by Kenji Wada; Ryuta Tomoyose; Teruyuki Kondo; Take-aki Mitsudo (pp. 72-79).

Combination of an animosilsesquioxane ligand, ruthenium complexes, and titania or silica followed by the controlled calcination afforded porous oxides having both micro- and mesopores. These oxides showed catalytic activities towards the hydroformylation of 1-octene with high linear selectivity of aldehyde.The controlled calcination of ruthenium complexes together with an aminosilsesquioxane ligand (1) at 823K in air stream for 4h afforded porous silicas including monodispersed ruthenium oxide nanoparticles with high surface areas and uniformly controlled micropores. Bimodal porous oxides with both meso- and micropores were prepared by the impregnation of Ru complexes and1 onto titania (JRC-TIO-4) or silica (JRC-SIO-1), followed by the careful calcination at 823K. These bimodal catalysts showed higher activity towards hydroformylation of 1-octene (C₉-aldehydes yield up to 31%, linear selectivity up to 95% in CO 20atm, H₂ 25atm at 403K for 20h with 1.5mol% Ru catalyst) than the catalysts prepared without an aminosilsesquioxane ligand.

Keywords: Hydroformylation; 1-Octene; Porous catalysts; Ruthenium; Metal oxide nanoparticles; Silsesquioxane ligand

Dehydrogenation of propane combined with selective hydrogen combustion over Pt-Sn bimetallic catalysts by Shinji Kaneko; Tsuyoshi Arakawa; Masa-aki Ohshima; Hideki Kurokawa; Hiroshi Miura (pp. 80-87).

Dehydrogenation of propane combined with selective hydrogen combustion was studied over supported Pt-Sn bimetallic catalysts. A catalytic test for normal dehydrogenation was also carried out as part of the proposed process. Pt/Al₂O₃ modified with Sn and Zn was found to be suitable for both of these two reactions. In the normal dehydrogenation, conversions equal to the calculated equilibrium conversion were achieved with almost complete selectivity for propylene. Optimization of catalyst composition was done by addition of various amounts of Sn to Pt/Al₂O₃ and Pt/Zn-Al-O. For dehydrogenation combined with hydrogen combustion, selective hydrogen combustion was achieved over Pt-Sn bimetallic catalysts. Moreover, a stable conversion higher than that of equilibrium for normal dehydrogenation was obtained using Pt-Sn/Zn-Al-O under certain reaction conditions.Dehydrogenation of propane combined with selective hydrogen combustion was studied over supported Pt-Sn bimetallic catalysts. A catalytic test for normal dehydrogenation was also carried out as part of the proposed process. Pt/Al₂O₃ modified with Sn and Zn was found to be suitable for both of these two reactions. In the normal dehydrogenation, conversions equal to the calculated equilibrium conversion were achieved with almost complete selectivity for propylene. Optimization of catalyst composition was done by addition of various amounts of Sn to Pt/Al₂O₃ and Pt/Zn-Al-O. For dehydrogenation combined with hydrogen combustion, selective hydrogen combustion was achieved over Pt-Sn bimetallic catalysts. Moreover, a stable conversion higher than that of equilibrium for normal dehydrogenation was obtained using Pt-Sn/Zn-Al-O under certain reaction conditions.

Keywords: Dehydrogenation of propane; Selective hydrogen combustion; Pt-Sn bimetallic catalysts; Zn-Al-O support

Dehydrogenation of long chain paraffins over supported Pt-Sn-K/Al₂O₃ catalysts: A study of the alumina support effect by Songbo He; Chenglin Sun; Ziwu Bai; Xihai Dai; Bin Wang (pp. 88-98).

The support effect on the Pt-Sn-K/Al₂O₃ catalysts for the long chain paraffins dehydrogenation to mono-olefins has been investigated by the test dehydrogenation reaction of n-octadecane. The catalysts were characterized by using different techniques: BET, MIP, XRD, TEM, SEM, CO-chemisorption, H₂-TPR, H₂-TPD, NH₃-TPD and TG-DTA. Results show that the pore structure and the surface characteristic of the alumina supports strongly affect the catalytic performance. The support effect can be divided into three parts: (I) the BET and pore size distribution govern the Pt dispersion of the catalysts, resulting in influencing the dehydrogenation activity; (II) the inherent acidity controls the acidity of the catalysts, bringing on the different product selectivity; (III) the pore volume provides the effective capability for carbon deposition, thus changing the lifetime of the catalysts. These functions should be adjusted for the alumina supports to achieve an optimal catalytic performance. The ideal catalysts were selected to test the lifetime of the catalysts on the dehydrogenation of n-C₁₆–C₁₉. High activity (the average conversion is 11.6%) and perfect selectivity (the average selectivity is 92%) were exhibited during the reaction time of 960h.The alumina support effect can be divided into three parts: (I) the BET and PSD govern the Pt dispersion of the catalysts; (II) the inherent acidity controls the acidity of the catalysts; (III) the pore volume provides the effective capability for carbon deposition. These functions should be adjusted to achieve an optimal catalytic dehydrogenation performance.

Keywords: Dehydrogenation; Long chain paraffins; Alumina support effect; Pore size distribution; Pt-Sn catalysts

Gold complexes as catalysts: Chemoselective hydrogenation of nitroarenes by Avelino Corma; Camino González-Arellano; Marta Iglesias; Félix Sánchez (pp. 99-102).

The reduction of a wide range of organic nitro compounds to the corresponding amines in good to excellent yields has been achieved using Au(III)–Schiff base and Au(I) catalysts. This method is mild, exceedingly efficient and highly selective. The azoxy, azo and hydrazo compounds, as the usual side products of reduction under basic conditions were not observed in the reaction system.Nitro groups on different compounds – containing double bonds, carbonyl, nitrile or halide groups – have been successfully hydrogenated with well-defined homogeneous gold and palladium complexes as catalysts using a batch reactor under low H₂ pressure. Gold complexes show high chemoselectivity towards reduction of the nitro group at near-complete conversion of the substrate. The corresponding amino derivatives are isolated in high yields.

Keywords: Gold; Catalysis; Homogeneous; Selective hydrogenation; Nitro compounds

Catalytic behavior and kinetic features of FeO_x/SBA-15 catalyst for selective oxidation of methane by oxygen by Qinghong Zhang; Yang Li; Dongli An; Ye Wang (pp. 103-111).

FeO_x/SBA-15 catalysts with low Fe contents can catalyze the selective oxidation of methane to formaldehyde efficiently. Isolated Fe species mainly account for the selective formation of HCHO. This report proposes that the Fe^II sites generated during the reaction function as the active centers for the activation of O₂, forming active oxygen species for the conversion of CH₄ to HCHO.FeO_x/SBA-15 catalysts with different iron contents were studied for the selective oxidation of methane by oxygen. The catalyst with an iron content of 0.05wt% exhibited the highest single-pass formaldehyde yield (∼2% at 898K). The selectivity to formaldehyde and the specific site rate for formaldehyde formation decreased with increasing iron content. The structure-performance correlation suggests that the isolated iron species account for the selective oxidation of methane to formaldehyde, whereas the Fe_mO_n clusters are less active and the crystalline Fe₂O₃ mainly catalyzes the complete oxidation of methane. Kinetic investigations over the 0.05wt% FeO_x/SBA-15 catalyst reveal that formaldehyde is the major primary product, and the consecutive oxidation of formaldehyde produces carbon monoxide as the main by-product. The reaction orders with respect to methane and oxygen were 1.0 and 0.20, respectively, and the activation energy was 102kJmol⁻¹, which was significantly lower than those reported for other catalysts such as MoO_x/SBA-15. Pulse reaction studies clarify that methane can react with the lattice oxygen but the products are only CO and CO₂. Thus, the lattice oxygen cannot be responsible for formaldehyde formation. It is proposed that the activation of molecular oxygen on the reduced iron sites generated by methane molecules produces active oxygen species for the selective oxidation of methane.

Keywords: Methane; Selective oxidation; Oxygen; Formaldehyde; Iron catalyst; SBA-15

Corrigendum to “Ni/SiO₂ catalysts prepared with ethylenediamine nickel precursors: Influence of the pretreatment on the catalytic properties in glucose hydrogenation” [Appl. Catal. A: Gen. 318 (2007) 45–53] by Sabine Schimpf; Catherine Louis; Peter Claus (pp. 112-112).

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Applied Catalysis A, General (v.356, #1)