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Applied Catalysis A, General (v.316, #2)

Editorial Board (pp. co2).

Contents (pp. iii-vii).

Selective hydrogenation of citral with transition metal complexes in supercritical carbon dioxide by Ruixia Liu; Fengyu Zhao; Shin-ichiro Fujita; Masahiko Arai (pp. 127-133).

The activity and selectivity of the transition metal complexes formed from Ru, Rh, Pd and Ni with triphenylphosphine (TPP) have been investigated for hydrogenation of citral in supercritical carbon dioxide (scCO₂). High activities are obtained with Ru/TPP and Pd/TPP catalysts, and the overall activity is in the order of Pd≈Ru>Rh>Ni. The Ru/TPP complex is highly selective to the formation of unsaturated alcohols of geraniol and nerol. In contrast, the Pd/TPP catalyst is more selective to partially saturated aldehydes of citronellal. Furthermore, the influence of several parameters such as CO₂ and H₂ pressures, N₂ pressure and reaction time has been discussed. CO₂ pressure has a significant impact on the product distribution, and the selectivity for geraniol and nerol can be enhanced from 27% to 75% with increasing CO₂ pressure from 6 to 16MPa, while the selectivity for citronellol decreases from 70% to 20%. Striking changes in the conversion and product distribution in scCO₂ could be interpreted with variations in the phase behavior and the molecular interaction between CO₂ and the substrate in the gas phase and in the liquid phase.High activities are obtained with Ru/TPP complexes for hydrogenation of citral in supercritical carbon dioxide (scCO2). CO2 pressure has a significant impact on the product selectivity. Striking changes in the conversion and selectivity in scCO2 could be interpreted with the variations in the phase behavior and the molecular interaction between CO2 and the substrate. ▪

Keywords: Selective hydrogenation; Citral; Transition metal complexes; Supercritical carbon dioxide; Phase behavior

Effect of surface Na⁺ or K⁺ ion exchange on hydrodesulfurization performance of MCM-41-supported Ni–W catalysts by Xiang Li; Anjie Wang; Sheng Zhang; Yongying Chen; Yongkang Hu (pp. 134-141).

Ni–W hydrodesulfurization (HDS) catalysts supported on MCM-41 synthesized from two different silica sources (sodium silicate hydrate and tetraethylorthosilicate) as well as on Na⁺ or K⁺ ion exchanged MCM-41 were prepared. These catalysts were used to investigate the influence of the surface properties of MCM-41 on the performance of HDS catalysts with DBT as the model molecule. The XRD and N₂ adsorption results indicated that the MCM-41 prepared from tetraethylorthosilicate (MCM-41(T)) exhibited the best structural properties. The mesostructure of MCM-41 synthesized from sodium silicate (MCM-41(S)) remained after ion exchange with Na₂C₂O₂ and K₂C₂O₂. Both pyridine FT-IR and Hammett indicators showed that only MCM-41(S) possessed some Brönsted and Lewis acid sites. Ni–W/MCM-41(S) showed the highest HDS and hydrogenation activities. The introduction of Na⁺ and K⁺ strongly inhibited the hydrogenation activity of Ni–W/MCM-41(S) but enhanced its hydrogenolysis activity. UV–vis and TPR studies indicated that the introduction of Na⁺ and K⁺ into MCM-41(S) may lead to the segregation of surface Ni species and may hinder the reducibility of the supported Ni–W oxides. Spillover hydrogen, which is “trapped�? by Na⁺ and K⁺, may play an important role in the HDS activity and selectivity of Ni–W catalysts.The introduction of Na⁺ or K⁺ strongly inhibited the hydrogenation activity and reducibility of Ni–W/MCM-41 but enhanced its hydrogenolysis activity. Spillover hydrogen, which is “trapped�? by Na⁺ and K⁺, may play an important role in the HDS activity and selectivity of Ni–W catalysts. ▪

Keywords: MCM-41; Ni–W; Ion exchange; Hydrodesulfurization; Na; ⁺; K; ⁺; Dibenzothiophene

Gas-phase epoxidation of propylene through radicals generated by silica-supported molybdenum oxide by Zhaoxia Song; Naoki Mimura; Juan J. Bravo-Suárez; Tomoki Akita; Susumu Tsubota; S. Ted Oyama (pp. 142-151).

It was found that silica-supported molybdenum oxide was high effective for the epoxidation of propylene among various silica-supported metal oxides. The post-catalytic bed volume played an important role in its formation. On a MoO_x/SiO₂ with 0.255mmol/g-SiO₂, a propylene conversion of 17.6% and a PO selectivity of 43.6% were obtained at 5atm, 573K and flow rates of C₃H₆/O₂/He=10/5/10cm³min⁻¹. The characterization studies indicated that crystalline MoO₃ nano-particle species was more effective for propylene epoxidation to PO than molecularly dispersed Mo oxide species. The reaction mechanism of propylene epoxidation on MoO_x/SiO₂ catalysts is hypothesized to involve gas-phase radicals generated at relatively low temperature by the dispersed molybdenum oxide species. These radicals participated in homogeneous reactions with molecular oxygen to produce propylene oxide.Silica-supported molybdenum oxide was high effective for the epoxidation of propylene to propylene oxide (PO) using O2 as an oxidant. The post catalytic-bed volume played an important role in PO formation. Crystalline MoO3 nano-particle species was effective for the propylene epoxidation. ▪

Keywords: Epoxidation; Propylene oxide; Silica-supported molybdenum oxides; Post-catalytic reaction; Radical reaction

Application of sulfonic acid functionalized MCM-41 materials—Selectivity changes in various probe reactions by Bulcsú Rác; Mariann Nagy; István Pálinkó; �?rpád Molnár (pp. 152-159).

MCM-41 mesoporous ordered silica materials with covalently anchored propanesulfonic acid groups with varying pore diameters (1.6–3.5nm) were synthesized. Two samples were prepared in the presence of appropriate templating agents (hexadecyltrimethylammonium chloride, decyltrimethylammonium bromide). After template removal they were reacted with 3-mercaptopropyltrimethoxysilane followed by transforming the thiol groups by oxidation to sulfonic acid functions. Two other catalyst samples were also prepared by treatment with phenyltriethoxysilane before template removal and functionalization. Sample characterization was performed by physical (low-angle X-ray powder diffraction, nitrogen adsorption, and desorption) and chemical (acid–base titration) methods. Three catalytic transformations were studied. Highly selective formation of para-tert-butylphenol through the isomerization of the ortho isomer was found in the alkylation of phenol with 2-methylpropan-2-ol over three of the catalysts. In the pinacol rearrangement of meso-hydrobenzoine, the rates of formation of diphenylacetaldehyde produced through phenyl migration with much higher steric requirement, parallel the changes in pore sizes. The reactivity of three aromatic ketones (acetophenone, 2-acetylnaphtalene, and 3-acetylphenantrene) in the formation of cyclic ketals over three of the catalysts depends significantly on the steric bulk of the reacting molecules. Furthermore, reactivity of the molecules with larger ring size in competitive reactions decreased and even stopped almost completely after the first hour and only the smaller molecule reacted further. Molecular modeling indicated that steric requirements might have significant effects on the reactivity over MCM-41-based catalysts. The results are interpreted as resulting from the combined effect of structural features of catalyst samples, catalyst ageing, and diffusion limitations.Steric congestion in the channels of functionalized MCM-41 shown by molecular modeling, diffusion limitations, and catalyst ageing result in high selectivity and significant differences in reactivity in catalytic transformations. ▪

Keywords: Mesoporous silicas; Grafting; Propanesulfonic acid; Alkylation of phenol; Pinacol rearrangement; Cyclic ketals; Catalyst ageing; Diffusion limitation

Synthesis and characterization of high surface area molybdenum phosphide by Ruihua Cheng; Yuying Shu; Lin Li; Mingyuan Zheng; Xiaodong Wang; Aiqin Wang; Tao Zhang (pp. 160-168).

A high surface area molybdenum phosphide (MoP) was successfully synthesized by combining citric acid (CA) and temperature-programmed reduction (TPR) (CA-TPR) method. Reduction of the precursor which was modified by citric acid produced MoP with a high surface area of 122.0m²g⁻¹ under optimum conditions. Fourier transform infrared (FTIR) results showed that the chelating interaction between the moderate amount of citric acid and the molybdenum ion was effective in suppressing the aggregation of Mo during drying through the formation of a molybdenum citrate, which was decomposed in calcination. Reduction of the precursor from the CA-TPR method showed an obvious decrease in degree of the aggregation of the MoP particles when compared to that from the conventional TPR method. The MoP prepared by the CA-TPR method was characterized by X-ray diffraction (XRD), N₂ adsorption–desorption, TPR, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and CO adsorption microcalorimetry. An increase in reduction temperature led to the formation of MoP crystalline and a change of morphology. The increase of surface area in the reduction process was a result of the formation of pores. The porous MoP from the CA-TPR method had a higher CO chemisorption uptake than from the conventional TPR method, indicating that the high surface area MoP possessed more active sites. The preliminary testing showed that the high surface area MoP exhibited a superior activity for hydrazine decomposition with a conversion of 85%, which was much higher than the conventional MoP of 55%.A high surface area molybdenum phosphide (MoP) was successfully synthesized by combining citric acid (CA) and temperature-programmed reduction (CA-TPR) method. The porous MoP from the CA-TPR method had a higher CO chemisorption uptake and activity for hydrazine decomposition. ▪

Keywords: Molybdenum phosphide; High surface area; CO adsorption; Microcalorimetry; Hydrazine decomposition

Preferential CO oxidation over activated carbon supported catalysts in H₂-rich gas streams containing CO₂ and H₂O by Eyüp Şimşek; Şeyma Özkara; A. Erhan Aksoylu; Z. Ilsen Önsan (pp. 169-174).

Selective CO oxidation (PROX) was studied at 423K over 1% Pt–0.25% SnO_x and 1% Pt–1% CeO_x catalysts supported on un-oxidized and oxidized activated carbon (AC) using feed mixtures simulating the reformate coming from fuel processors. Effects of the addition of 15% CO₂ or (15% CO₂+10% H₂O) into feed mixtures containing 1% CO, 1% O₂, 60% H₂ and He were determined for nine different AC-supported catalysts, and the results were compared with those obtained with pure H₂-rich feed. Unlike other PROX catalysts having oxide supports, introduction of CO₂ into pure feed drastically increased CO conversion on all nine catalysts supported on oxidized or un-oxidized AC regardless of impregnation strategy.1% Pt–0.25% SnO_x supported on HNO₃-oxidized AC stands out as a potential candidate for commercial use in PROX since it yields 100% CO conversion under realistic feed conditions. 1% Pt–1% CeO_x catalysts prepared by sequential or co-impregnation and supported on air-oxidized AC also give 100% CO conversion in H₂-rich feed containing (CO₂+H₂O) during extended run times and hence hold promise as PROX catalysts.Selective CO oxidation was studied at 423 K over 1%Pt-0.25%SnO_x and 1%Pt-1%CeO_x catalysts supported on un-oxidized and oxidized activated carbon. Introduction of CO₂ and (CO₂ + H₂O) into feed containing 1%CO, 1%O₂, 60%H₂ and helium drastically increased CO conversion to 100 per cent. 1%Pt-0.25%SnO_x supported on HNO₃-oxidized AC and 1%Pt-1%CeO_x supported on air-oxidized AC hold promise as potential PROX catalysts. ▪

Keywords: Selective CO oxidation; PROX; Hydrogen clean-up; Fuel processors; PEM fuel cells

Study of Ni and Pt catalysts supported on α-Al₂O₃ and ZrO₂ applied in methane reforming with CO₂ by Francisco Pompeo; Nora N. Nichio; Mariana M.V.M. Souza; Deborah V. Cesar; Osmar A. Ferretti; Martin Schmal (pp. 175-183).

Ni and Pt catalysts supported on α-Al₂O_3, α-Al₂O₃-ZrO₂ and ZrO₂ were studied in the dry reforming of methane to produce synthesis gas. All catalytic systems presented well activity levels with TOF (s⁻¹) values between 1 and 3, being Ni based catalysts more active than Pt based catalysts. The selectivity measured at 650°C, expressed by the molar ratio H₂/CO reached values near to 1. Concerning stability, Pt/ZrO₂, Pt/α-Al₂O₃-ZrO₂ and Ni/α-Al₂O₃-ZrO₂ systems clearly show lower deactivation levels than Ni/ZrO₂ and Ni or Pt catalysts supported on α-Al₂O₃. The lowest deactivation levels observed in Ni and Pt supported on α-Al₂O₃-ZrO₂, compared with Ni and Pt supported on α-Al₂O₃ can be explained by an inhibition of reactions leading to carbon deposition in systems having ZrO₂. These results suggest that ZrO₂ promotes the gasification of adsorbed intermediates, which are precursors of carbon formation and responsible for the main deactivation mechanism in dry reforming reaction.The catalysts studied presented well activity levels, being Ni based catalysts more active than Pt based catalysts. The lowest deactivation levels were observed in α-Al₂O₃-ZrO₂ systems. These results suggest that ZrO₂ promotes the gasification of adsorbed intermediates, which are precursors of carbon formation and responsible for the main deactivation mechanism. ▪

Keywords: Methane; Carbon dioxide; Syngas; Reforming; Nickel; Platinum

Surface structure and catalytic performance of niobium oxides supported on titania by Thomas Onfroy; Olga V. Manoilova; Saeed B. Bukallah; David M. Hercules; Guillaume Clet; Marwan Houalla (pp. 184-190).

The surface structure and activity of catalytic systems based on niobium oxide supported on titania were investigated. A series of catalysts with Nb content up to 3.6atoms/nm² was prepared by incipient wetness impregnation of the titania support with niobium oxalate solutions. Characterization of the system by X-ray diffraction (XRD) and Raman spectroscopy studies did not show evidence of niobium oxide formation. Surface analysis was performed by X-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS), Raman and infrared spectroscopy. These results were correlated with Brønsted acidity and catalytic activity determined in our previous study. A direct correlation between the catalytic activity and the abundance of Brønsted acid sites had been observed. Analysis of the surface structure by infrared spectroscopy showed a similar evolution for the intensity of the band attributed to polymerized NbO_x.The surface structure and activity of catalytic systems based on niobium oxide supported on titania were characterized by XRD, XPS, Ion Scattering spectroscopy (ISS), Raman and infrared spectroscopy. The catalytic activity for propanol dehydration and the abundance of Brønsted acid sites were directly correlated and their development is consistent with that of the intensity of the infrared band attributed to polymerized NbO_x. ▪

Keywords: Titania-supported niobium oxide; Brønsted acidity; Surface analysis; Infrared spectroscopy; Raman spectroscopy; Propanol dehydration

Catalytic activity of a dinuclear manganese complex (MnMeTACN) on the oxidation of ethyl linoleate by Z.O. Oyman; W. Ming; R. van der Linde (pp. 191-196).

Catalytic activity of a dinuclear manganese-based complex [Mn₂^IV(μ-O)₃L₂](PF₆)₂ (MnMeTACN) (L=1,4,7-trimethyl-1,4,7-triazacyclononane), and its combination with a polyamine, 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA), was investigated on the oxidation of ethyl linoleate (EL). When MnMeTACN was molecularly mixed with EL in a co-solvent (methanol), MnMeTACN alone was found to be a very active catalyst for the oxidation of unpurifed EL (containing a small amount of hydroperoxides), similar to the catalytic activity of a Co-based catalyst. For purified EL (free of hydroperoxides), the addition of tert-butyl hydroperoxide was necessary to rapidly initiate the EL oxidation. A tentative catalytic cycle for MnMeTACN was proposed on the basis of electrospray ionization mass spectrometry (ESI-MS) investigation. The existence of HMTETA significantly accelerated the decomposition of the formed hydroperoxides into alkoxy free radicals, which in turn led to a high level of volatile aldehyde byproducts due to β-scission reactions.The catalytic activity of a dinuclear manganese-based complex, [Mn^IV₂(μ-O)₃L₂](PF₆)₂ (MnMeTACN) on the oxidation of ethyl linoleate (EL) was found to be similar to that of a Co-based catalyst. The presence of hydroperoxide was necessary to rapidly initiate the EL oxidation. A tentative catalytic cycle for MnMeTACN was proposed on the basis of ESI-MS investigation. ▪

Keywords: Alkyd coating; Mn-catalyst; Oxidation; Hydroperoxide; Catalytic activity

Novel aspects of the physical chemistry of Co/SiO₂ Fischer–Tropsch catalyst preparations by I. Puskas; T.H. Fleisch; J.A. Kaduk; C.L. Marshall; B.L. Meyers; M.J. Castagnola; J.E. Indacochea (pp. 197-206).

Co/SiO₂ catalysts were prepared by aqueous cobalt nitrate impregnations of silicas with different surface areas to study the effect of the support surface area on the reactions occurring during impregnation and calcination and to define the stage and mode of metal–support interactions. Cobalt silicate formation is the result of silica migration and bond formation between CoO and SiO₂. The migration of silica occurs in a relatively short time period during the thermal decomposition of cobalt nitrate, while simultaneous migration and oxidation of CoO to Co₃O₄ aggregates also occurs. The extensive migration of silica is attributed to strong attraction between SiO₂ and CoO species, inducing the removal of silicic acid or silica molecules from the silica surface. ▪Co/SiO₂ catalysts were prepared by aqueous cobalt nitrate impregnations of silicas with different surface areas to study the effect of the support surface area on the reactions occurring during impregnation and calcination and to define the stage and mode of metal–support interactions. TPR analyses of samples calcined in dry air showed the presence of various quantities of cobalt silicate species, while cobalt silicate formation was not discernible by other analytical techniques. Our conclusion, confirmed in our later studies, is that cobalt silicate does not form during impregnation or calcination, but is created during the reduction in the TPR instrument. Because of these and other ambiguities of the TPR analyses, in our continuing studies we preferred alternative analytical approaches.These studies on the calcination stage resulted in the following unusual findings: (1) X-ray photoelectron spectroscopy revealed drastic decreases in the surface cobalt concentration after calcination of high surface silicas impregnated with cobalt nitrate solutions. (2) Infrared spectroscopy indicated much less than expected Co₃O₄ formation upon calcination if high surface area silica was the support. (3) A method was devised to calculate the surface areas of individual components in mixtures. The calculations indicated about 20% surface area losses for the silica in calcined catalysts. (4) Scanning electron micrographs of a calcined catalyst on high surface area silica support showed smaller-sized decorations around the larger silica particles. Energy-dispersive X-ray analysis of the decorations showed Si as major, and Co as a minor component. Pure Co₃O₄ phases were not found by EDX analyses of these decorations. These four seemingly unrelated findings are attributed to a common cause: silica migration and weak bond formation between CoO and SiO₂. The extent of surface area losses (i.e. the extent of silica migration) is about an order of magnitude greater in CoO_x–SiO₂ catalysts than in analogously treated SiO₂. The migration of silica must have occurred in a relatively short time period during the thermal decomposition of cobalt nitrate, while simultaneous migration and oxidation of CoO to Co₃O₄ aggregates also occurred. The CoO species intercepted by SiO₂ were unable to oxidize, resulting in reduced quantity of Co₃O₄ formation. The extensive migration of silica is attributed to strong attraction between SiO₂ and CoO species, inducing the removal of silicic acid or silica molecules from the silica surface.

Keywords: Cobalt; Silica; Fischer–Tropsch; Migration

Nickel distribution in (Ni,Mg)/Al-layered double hydroxides by J.A. Rivera; G. Fetter; Y. Jiménez; M.M. Xochipa; P. Bosch (pp. 207-211).

Hydrotalcites are anionic clays whose structure is lamellar. They are constituted by pairs of octahedral divalent and trivalent cations. The substitution of the divalent by the trivalent cations generates a charge excess which has to be compensated by anions such as carbonates, nitrates or iodine among others. The location of the trivalent cations is uncertain as it may depend on the synthesis method. Although hydrotalcites may be synthesized through conventional precipitation from the corresponding salts the obtained cation distribution may be altered in presence of microwave irradiation.In hydrotalcites synthesized in presence of microwave irradiation, magnesium and aluminum are not homogeneously distributed: Aluminum is selectively retained in the particle core. If zinc or nickel are included in the synthesis mixture, zinc, which is a large cation, remains in the pore mouths generating lattice strain. Most of it, then, forms zinc oxide crystallites. Instead, nickel is able to reach the inner part of the hydrotalcite particle. With calcinations, 450°C/4h, hydrotalcite is never fully destroyed.In hydrotalcites synthesized in presence of microwave irradiation, magnesium and aluminum are not homogeneously distributed: aluminum is selectively retained in the particle core. If zinc or nickel are included in the synthesis mixture, zinc, which is a large cation, remains in the pore mouths generating lattice strain. Instead, nickel is able to reach the inner part of the hydrotalcite particle. ▪

Keywords: Hydrotalcite; Microwave irradiation; Microporous materials; Zinc; Aluminum; Magnesium; Nickel; Nanometrical NiO

HDS of thiophene over CoMo/AlMCM-41 with different Si/Al ratios by Marcelo J.B. Souza; Bojan A. Marinkovic; Paula M. Jardim; Antonio S. Araujo; Anne M.G. Pedrosa; Roberto R. Souza (pp. 212-218).

A series of AlMCM-41 molecular sieves with different Si/Al ratios were synthesized followed by the deposition of cobalt and molybdenum oxides on these mesoporous supports by co-impregnation. These materials were characterized by X-ray diffraction (XRD), transmission electron microscopy and selected area electron diffraction (TEM/SAED), X-ray fluorescence (XRF), and nitrogen adsorption. Hydrodesulphurisation (HDS) of thiophene was carried out at 350°C in a fixed bed continuous flow micro reactor coupled on line to a gas chromatograph. The main products of HDS of thiophene were H₂S, isobutene, 1-butene, n-butane, 2-butene-trans, and 2-butene-cis. It was observed that the reactivity of the as-synthesized catalysts is a direct function of the Si/Al ratio, nature and concentration of the active species on the mesoporous supports. ▪A series of AlMCM-41 molecular sieves with different Si/Al ratios were synthesized followed by the deposition of cobalt and molybdenum oxides on these mesoporous supports by co-impregnation. Such materials were further calcined and catalysts with 15wt.% of cobalt and molybdenum and a Co/(Co+Mo) atomic ratio of 0.30 were obtained. These materials were characterized by X-ray diffraction (XRD), transmission electron microscopy and selected area electron diffraction (TEM/SAED), X-ray fluorescence (XRF), and nitrogen adsorption. Hydrodesulphurisation (HDS) of thiophene was carried out at 350°C in a fixed bed continuous flow micro reactor coupled on line to a gas chromatograph. The main XRD peaks of MCM-41 phase were observed in all samples and peaks due to MoO₃ and CoMoO₄ phases were also identified from XRD results. It was found that the as-synthesized catalysts presented reasonable conversion results for HDS of thiophene, when compared to other supported catalysts. The main products of HDS of thiophene were H₂S, isobutene, 1-butene, n-butane, 2-butene-trans, and 2-butene-cis. It was observed that the reactivity of the as-synthesized catalysts is a direct function of the Si/Al ratio, nature and concentration of the active species on the mesoporous supports.

Keywords: AlMCM-41; Si/Al ratio; Cobalt and molybdenum; Hydrodesulphurization

One-pot synthesis of Ga-SBA-15: Activity comparison with Ga-post-treated SBA-15 catalysts by Z. El Berrichi; B. Louis; J.P. Tessonnier; O. Ersen; L. Cherif; M.J. Ledoux; C. Pham-Huu (pp. 219-225).

Gallium containing SBA-15 mesoporous materials with different Si/Ga ratio were synthesized using an in situ sol–gel procedure with an aqueous solution of Ga(NO₃)₃.The catalytic activity of these Ga-SBA-15 materials has been evaluated in the Friedel–Crafts acylation of anisole with benzoyl chloride and in the alkylation of benzene. The activity was compared with the one of Ga-modified SBA-15 by post-treatment. ▪Gallium containing SBA-15 mesoporous materials with different Si/Ga ratio were synthesized using an in situ sol–gel procedure with an aqueous solution of Ga(NO₃)₃. The materials were characterised by means of elemental analysis, BET, XRD, TEM, and H/D isotope exchange techniques. It appears that depending their loading, stable Ga-species were either anchored to the siliceous matrix of SBA-15 or introduced in the framework via isomorphous substitution, thus generating acid properties in their host material.The catalytic activity of Ga-SBA-15 materials has been evaluated in the Friedel–Crafts acylation of anisole with benzoyl chloride and in the alkylation of benzene using benzyl chloride as alkylating agent. The activity of these catalysts was compared with the one of Ga-modified SBA-15 by post-treatment. A complete conversion of benzyl chloride over Ga-SBA-15 materials has been reached after 3h of reaction with a 75% selectivity toward diphenylmethane. In contrast to Ga-samples prepared by post-treatment, in situ Ga-SBA-15 present a lower stability in the acylation reaction. However, the catalytic results indicate that Ga-SBA-15 mesoporous materials can be used as versatile and stable acid catalysts for Friedel–Crafts reactions with appropriate behavior depending on their preparation mode.

Keywords: Gallium; SBA-15; Alkylation; Acylation; Acid catalyst; Friedel–Crafts

Combination of flame synthesis and high-throughput experimentation: The preparation of alumina-supported noble metal particles and their application in the partial oxidation of methane by Stefan Hannemann; Jan-Dierk Grunwaldt; Peter Lienemann; Detlef Günther; Frank Krumeich; Sotiris E. Pratsinis; Alfons Baiker (pp. 226-239).

Flame spray pyrolysis has been combined with high-throughput experimentation for the preparation and screening of alumina-supported multi-metal (Pt, Pd, Ru and Rh) catalysts suitable for the partial oxidation of methane. Structural properties, including possible alloy formation, were investigated applying STEM-EDXS as well as EXAFS spectroscopy.▪Mono and multi-noble metal particles on Al₂O₃ were prepared in one step by flame spray pyrolysis (FSP) of the corresponding noble metal precursors dissolved in methanol and acetic acid (v/v 1:1) or xylene. The noble metal loading of the catalysts was close to the theoretical composition as determined by WD-XRF and LA-ICP-MS. The preparation method was combined with high-throughput testing using an experimental setup consisting of eight parallel fixed-bed reactors. Samples containing 0.1–5wt% noble metals (Ru, Rh, Pt, Pd) on Al₂O₃ were tested in the catalytic partial oxidation of methane. The ignition of the reaction towards carbon monoxide and hydrogen depended on the loading and the noble metal constituents. The selectivity of these noble metal catalysts towards CO and H₂ was similar under the conditions used (methane: oxygen ratio 2:1, temperature from 300 to 500°C) and exceeded significantly those of gold and silver containing catalysts.Selected catalysts were further analysed using XPS, BET, STEM-EDXS and XANES/EXAFS. The catalysts exhibited generally a specific surface area of more than 100m²/g, and were made up of ca. 10nm alumina particles on which the smaller noble metal particles (1–2nm, partially oxidized state) were discernible. XPS investigation revealed an enrichment of noble metals on the alumina surface of all samples. The question of alloy formation was addressed by STEM-EDXS and EXAFS analysis. In some cases, particularly for Pt–Pd and Pt–Rh, alloying close to the bulk alloys was found, in contrast to Pt–Ru being only partially alloyed. In situ X-ray absorption spectroscopy on selected samples was used to gain insight into the oxidation state during ignition and extinction of the catalytic partial oxidation of methane to hydrogen and carbon monoxide.

Keywords: Noble metal nanoparticles; Flame spray pyrolysis; Catalytic partial oxidation of methane; High-throughput experimentation; In situ; X-ray absorption spectroscopy; STEM; Alloys

Efficient catalysts with controlled porous structure obtained by anodic oxidation under spark-discharge by Florian Patcas; Waldemar Krysmann (pp. 240-249).

The anodic oxidation under spark discharge (ANOF technique) is presented as a promising alternative for the preparation of catalytic oxide layers on metallic supports. The influence of the substrate (Al, Ti, and Mg), electrolyte composition and the treatment time to obtain egg-shell catalysts with tailor-made properties for the effective oxydehydrogenation (ODH) of cyclohexane to cyclohexene is studied. Chromium, molybdenum and nickel were chosen as precursors for active species in order to obtain catalysts able to perform the substrate oxidation by electrophilic (chromium oxide), nucleophilic (molybdena) or both kind of oxygen species (nickel oxide). It was found that compared to nickel oxide, the chromium oxide containing egg-shell catalyst was less selective while the molybdenum oxide showed very high selectivity, but lower activity. The intrinsic activity of nickel containing egg-shell catalysts is an order of magnitude higher than that of a classic alumina supported nickel oxide catalyst obtained by impregnation. The selectivity to the intermediate cyclohexene is also favored on the egg-shell catalyst with a regular pore structure. Moreover, the selectivity performance of the catalysts can be improved by designing catalysts with shorter pores.The anodic oxidation under spark discharge (ANOF technique) is presented as a promising alternative for the preparation of catalytic oxide layers on metallic supports. The influence of the substrate (Al, Ti, and Mg), electrolyte composition and the treatment time to obtain egg-shell catalysts with tailor-made properties for the effective oxydehydrogenation (ODH) of cyclohexane to cyclohexene is studied. ▪

Keywords: Microstructured catalyst; Egg-shell catalyst; Anodic-spark oxidation; Cyclohexane oxydehydrogenation; Selectivity control

Characterisation of BN-supported palladium oxide catalyst used for hydrocarbon oxidation by G. Postole; B. Bonnetot; A. Gervasini; C. Guimon; A. Auroux; N.I. Ionescu; M. Caldararu (pp. 250-258).

Hexagonal boron nitride (BN), with a graphite-type structure and with surface area of 184m²/g was used as a support for palladium oxide (PdO/BN). About 1wt% of palladium was deposited on BN by incipient wetness method by using palladium nitrate as precursor. The support and the catalyst were characterized by BET, TEM, XRD, XPS, ICP, TG, TPD, in situ ac electrical conductivity and by ammonia adsorption microcalorimetry. Oxidation of propylene and methane were used as model reactions to study the catalytic properties of the PdO /BN catalyst. The BN support was practically inactive in propylene oxidation up to 400°C, while the onset of the oxidation was detected around 200°C on PdO/BN, which points out the role of the palladium in adsorption of the reactive hydrocarbon species. At the same time, this temperature is coincident with the increase of the electronic conductivity on both BN and PdO/BN samples, which is important for oxygen adsorption/activation as electrophilic species. The catalyst was inactive in methane oxidation below 400°C. Only about 2% CH₄ conversion was observed at 400°C, increasing sharply up to 87% at 550°C with methane transformation only to CO₂ and water.Hexagonal BN (with graphite structure) was used as a support for a palladium catalyst (1 wt% Pd). Both solids were characterized by BET, TEM, XRD, XPS, ICP, TG, TPD, in situ ac electrical conductivity and ammonia adsorption microcalorimetry. Propylene and methane oxidation were used to study the catalytic properties of Pd/BN. ▪

Keywords: Boron nitride; Palladium catalyst; In situ; electrical conductivity; Hydrocarbon oxidation; Acidity

Corrigendum to “Plasma generation of supported metal catalysts�? [Appl. Catal. A: Gen. 237 (2002) 41–51] by Hyunsup Shim; Jonathan Phillips; I.M. Fonseca; S. Carabineiro (pp. 259-259).

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Applied Catalysis A, General (v.316, #2)