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Applied Catalysis A, General (v.318, #)

Editorial Board (pp. co2).

Contents (pp. iii-x).

Stereoselective hydrogenation of terpenes using platinum-based catalysts by Mónica L. Casella; Gerardo F. Santori; Albertina Moglioni; Virginia Vetere; José F. Ruggera; Graciela Moltrasio Iglesias; Osmar A. Ferretti (pp. 1-8).

The catalytic hydrogenation of some terpenes is discussed. Catalysts employed were silica supported Pt and Pt modified by tin addition. Selected substrates were α-pinene, verbanone, fenchone, camphor and verbenone. The catalytic systems studied allow the control of reaction stereoselectivity. In sterically hindered terpenones, the topography of the molecule resulted of fundamental importance in controlling the stereoselectivity of the reaction. ▪In the present paper, the catalytic hydrogenation of some terpenes is discussed. Catalysts employed were silica supported Pt and Pt modified by tin addition using techniques derived from surface organometallic chemistry on metals. Selected substrates were α-pinene, verbanone, fenchone, camphor and verbenone. The catalytic systems studied allow the control of reaction stereoselectivity. The hydrogenation of α-pinene led selectively to cis-pinane, and it was possible to observe that the modification of Pt/SiO₂ with Sn caused an important decrease of the catalytic activity; this fact can be explained by combined electronic and geometrical effects. In sterically hindered terpenones (fenchone and camphor), the topography of the molecule resulted of fundamental importance in controlling the stereoselectivity of the reaction. In verbenone hydrogenation, the Pt/SiO₂ catalyst allowed to obtain cis-verbanone with high yield and catalysts modified with Sn led to the formation of a principal product ( cis-verbanol) different than the one obtained by chemical reduction with NaBH₄ ( cis-verbenol).

Keywords: Platinum–tin catalysts; Surface organometallic chemistry; Hydrogenation; Stereoselectivity; α-Pinene; Camphor; Verbenone

In situ X-ray investigations on AgIn/SiO₂ hydrogenation catalysts by Frank Haass; Michael Bron; Hartmut Fuess; Peter Claus (pp. 9-16).

In this paper, Ag/SiO₂ and AgIn/SiO₂ hydrogenation catalysts are investigated by means of in situ EXAFS under industrial relevant conditions (i.e., 20bar and 250°C). For this purpose, a new in situ cell has been developed, which is also described in this paper. ▪The structure of bimetallic catalysts based on silver and indium has been studied during the hydrogenation of acrolein by in situ X-ray absorption spectroscopy. A novel in situ cell, capable of performing X-ray absorption experiments in transmission geometry on catalyst powders under reaction conditions (i.e., temperatures up to 500°C and pressures up to 20bar, corrosive atmosphere), was developed for this purpose. Ag K- and In K-spectra were recorded during the acrolein hydrogenation. Changes in the indium valence were observed during the reaction by XANES analysis, whereas silver remained redox inert. The evaluation of the EXAFS spectra exhibited a characteristic peak in r-space at ca. 3Å during acrolein hydrogenation, which can be understood by a structure model consisting of AgIn clusters partly covered with adsorbed acrolein on the catalyst surface. It could be shown that the adsorbate-metal-distance is different for Ag/SiO₂ and AgIn/SiO₂ catalysts, which is most likely due to different adsorption geometries. Structural parameters of the catalyst under reaction conditions were determined by a quantitative EXAFS analysis.

Keywords: Hydrogenation catalysts; Bimetallic catalysts; Acrolein; X-ray absorption spectroscopy; Silver; Indium; In situ-spectroscopy

The influence of textural and structural properties of Pd/carbon on the hydrogenation of cis, trans, trans-1,5,9-cyclododecatriene by Amandine Cabiac; Gérard Delahay; Robert Durand; Philippe Trens; Dominique Plée; Alice Medevielle; Bernard Coq (pp. 17-21).

Carbon-supported palladium catalysts were prepared by ion-exchange and precipitation/deposition methods on various activated carbons. Pd/carbon catalysts with Pd particles ranging from 1.5 to 10nm were thus obtained. The liquid phase hydrogenation of c, t, t-1,5,9-cyclododecatriene was carried out on these catalysts. A structure-sensitivity was observed with a decrease of TOF on smallest Pd particles. The highest yield to half-hydrogenated cyclododecene was observed on large Pd particles (∼10nm).Pd/C catalysts were prepared by ion-exchange and precipitation/deposition methods on various activated carbons with Pd particles ranging from 1.5 to 10nm. The liquid phase hydrogenation of c, t, t-1,5,9-cyclododecatriene was carried out on these catalysts. A structure-sensitivity was observed with a decrease of TOF on smallest Pd particles. The highest yield to half-hydrogenated cyclododecene was observed on large Pd particles (∼10nm).▪

Keywords: Palladium; Carbon; Catalysts; Hydrogenation; Cyclododecatriene

Shape selectivity of MWW-type aluminosilicate zeolites in the alkylation of toluene with methanol by Satoshi Inagaki; Kohei Kamino; Eiichi Kikuchi; Masahiko Matsukata (pp. 22-27).

We investigated the alkylation of toluene with methanol over MCM-22 and ITQ-2 zeolites possessing an MWW structure. A high p-xylene selectivity was obtained by poisoning the external surface of ITQ-2 or MCM-22 with collidine. We concluded that both interlayer and intralayer 10MR micropores in the MWW structure caused the shape-selective formation of p-xylene in the alkylation of toluene with methanol.▪We investigated the alkylation of toluene with methanol at 250°C over MCM-22 and ITQ-2 zeolites possessing an MWW structure. Whereas ITQ-2, produced by the delamination of MCM-22 precursor, showed a poor p-xylene selectivity of 23% at 1.7% of the level of toluene conversion, a high p-xylene selectivity of 80% at 0.6% of the level of toluene conversion was obtained by poisoning the external surface of ITQ-2 with collidine. Similarly, MCM-22 treated with collidine showed a high p-xylene selectivity of 74% at 3.8% of the level of toluene conversion. We concluded that both interlayer and intralayer 10-membered ring (10MR) micropores in the MWW structure caused the shape-selective formation of p-xylene in the alkylation of toluene with methanol.

Keywords: MCM-22 zeolite; ITQ-2 zeolite; Alkylation of toluene with methanol; Shape selectivity; Collidine

Catalyst deactivation during thiophene HDS: The role of structural sulfur by Bas M. Vogelaar; Petr Steiner; Thomas F. van der Zijden; A. Dick van Langeveld; Sonja Eijsbouts; Jacob A. Moulijn (pp. 28-36).

The deactivation behavior of a Mo/Al₂O₃ and a NiMo/Al₂O₃ catalyst during the hydrodesulfurization of thiophene was investigated under gas-phase conditions. Four different deactivation mechanisms were considered: sintering and segregation of the active phase, blocking of the pore structure by coke deposition, poisoning of the active sites by coke and changes in the nature of the active sites induced by differences in pretreatment and reaction conditions. These mechanisms were investigated using quasi in situ XPS, analysis of the pore structure and coke content, and by measuring the HDS activity. During the thiophene HDS reaction, both catalysts show similar deactivation behavior: about 50% of the initial activity was lost during the first hours on stream. The extent of sintering/segregation and pore blocking was marginal and had no significant effect on the activity. A trend between the coke content and the deactivation was observed, but it is concluded that coke does not selectively poison the active sites. The main cause for the observed initial deactivation is the loss of sulfur from the active phase during the reaction. The number of sulfur groups and vacant sites on the catalysts is in equilibrium with the H₂S/H₂ ratio of the gas phase. Exposure to H₂S resulted in an increased initial activity or a (partial) reactivation, whereas exposure to H₂ caused a deactivation. It is concluded that the rate-determining step in the HDS of thiophene is catalyzed by structural sulfur; most probably, acidic SH groups facilitate the hydrogenation of the thiophenic ring.

Keywords: Deactivation; Hydrodesulfurization; Thiophene

DC magnetron sputter deposited vanadia catalysts for oxidation processes by M. Olea; I. Sack; V. Balcaen; G.B. Marin; H. Poelman; K. Eufinger; D. Poelman; R. De Gryse; J.S. Paul; B.F. Sels; P.A. Jacobs (pp. 37-44).

New model catalysts were prepared by applying DC magnetron sputter deposition of vanadia onto ZrO₂/SiO₂ and TiO₂/ZrO₂/SiO₂ supports and were characterized by XRD, EDX, XPS, ICP and catalytic activity towards propane and isobutane oxidative dehydrogenation. Titania interlayer enhances oxidative dehydrogenation activity and decreases the total oxidation side reactions. A Mars–van Krevelen mechanism is operative.▪New model catalysts were prepared by applying DC magnetron sputter deposition of vanadia onto ZrO₂/SiO₂ and TiO₂/ZrO₂/SiO₂ supports and were characterized by X-ray diffraction (XRD), X-ray energy dispersive spectrometry (EDX), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma emission spectroscopy (ICP) and catalytic activity towards propane and isobutane oxidative dehydrogenation. Titania interlayer enhances oxidative dehydrogenation activity and decreases the total oxidation side reactions. A Mars–van Krevelen mechanism is operative.

Keywords: DC magnetron sputtering; Vanadia-based catalysts; Oxidative dehydrogenation; Propane; Isobutane; XPS; ICP; TAP; Transient experiments; Steady-state experiments

Ni/SiO₂ catalysts prepared with ethylenediamine nickel precursors: Influence of the pretreatment on the catalytic properties in glucose hydrogenation by Sabine Schimpf; Catherine Louis; Peter Claus (pp. 45-53).

To overcome nickel leaching, Ni/SiO₂ catalysts (5, 10, and 20wt%) were prepared using nickel ethylenediamine complexes. In glucose hydrogenation, they show almost no leaching, but slightly lower activity (TOF) and lower yields to sorbitol compared to an industrial catalyst. The catalytic results depend on the pretreatment performed.▪Nickel catalysts prepared with different metal loadings (5, 10, and 20wt% Ni) by impregnation with nickel ethylenediamine complexes revealed small nickel particles (mean diameter: 2–3nm) after reduction, even for high metal loadings (20wt%). When used in the hydrogenation of glucose, these catalysts show almost no nickel leaching compared to a commercial Ni/SiO₂ catalyst (prepared by precipitation, 67wt% Ni), but they are slightly less active (TOF: 2 to 10×10⁻³s⁻¹) than a commercial nickel/silica catalyst (TOF: 14×10⁻³s⁻¹) and revealed lower yields to sorbitol (3–42% compared to 60%). The catalytic results depend on the pretreatment conditions performed. When the catalysts are calcined before reduction, higher conversion (19–45%) and selectivity to sorbitol (81–92%) are obtained than when they are directly reduced without calcination pretreatment (conversion: 10–16% and selectivity to sorbitol: 21–59%) after 5h of reaction time, respectively. The difference was ascribed to the fact that complete decomposition of the nickel ethylenediamine precursor was achieved only when calcination pretreatment was performed. Indeed, when the catalysts were directly reduced, X-ray photoelectron spectroscopy (XPS) revealed a nitrogen-compound probably responsible for lower conversion and higher selectivities to fructose and mannose, indicating Lobry de Bruyn-Alberda van Ekenstein rearrangement. However, no nickel sintering was observed in contrast to the catalyst calcined before reduction.

Keywords: Hydrogenation; Glucose; Sorbitol; Nickel catalysts; Leaching

Catalytic autothermal reforming of methane: Performance of a kW scale reformer using pure oxygen as oxidant by Stefan Rabe; Thanh-Binh Truong; Frédéric Vogel (pp. 54-62).

The autothermal low temperature catalytic partial oxidation of methane was investigated in a bench-scale reactor (1kW_th power) over a structured ruthenium catalyst (metal monolith support). Pure oxygen was used as the oxidant. Autothermal operation of the reactor was successfully demonstrated. The increase of the O/C ratio increased the average reactor temperature resulting in higher methane conversions. Similar results were obtained for the increase of the space velocity. The product gas generated was rich in hydrogen (65%), nitrogen-free and contained comparably low amounts of carbon monoxide (5%). The results revealed that the oxygen-blown reforming at low temperatures could be a well-suited process for the production of hydrogen in conjunction with a carbon dioxide sequestration.The autothermal low temperature catalytic partial oxidation of methane was investigated in a bench-scale reactor (1kW_th power) over a structured ruthenium catalyst (metal monolith support). Pure oxygen was used as the oxidant. Autothermal operation of the reactor was successfully demonstrated. Reforming efficiencies as well as possible applications of the oxygen-blown reforming are discussed. ▪

Keywords: Reforming; Catalytic partial oxidation; Hydrogen; Fuel processing; Ruthenium

Carbon nanotubes synthesis by the ethylene chemical catalytic vapour deposition (CCVD) process on Fe, Co, and Fe–Co/Al₂O₃ sol–gel catalysts by Kim Yên Tran; Benoît Heinrichs; Jean-François Colomer; Jean-Paul Pirard; Stéphanie Lambert (pp. 63-69).

The production of CNTs by CCVD was examined over Fe/Al₂O₃, Co/Al₂O₃, and Fe–Co/Al₂O₃ sol–gel catalysts. Best activity and selectivity in carbon nanotubes were obtained with Co/Al₂O₃. Metal–support interactions and metal oxide particle size are influenced by metal precursor nature. A correlation has been found between the metal oxide particle sizes, the diameter of the carbon nanotubes, and the catalytic activity. ▪The production of carbon nanotubes by the chemical catalytic vapour deposition, CCVD, process was examined over iron, cobalt, and a mixture of iron and cobalt supported on alumina catalysts synthesized by a one step sol–gel process. The catalysts were synthesized from several metal precursors, iron nitrate, cobalt and iron acetylacetonate, and cobalt acetate. Ethylene was used as the carbon source.The Co/Al₂O₃ catalysts showed better activity and selectivity in carbon nanotubes synthesis than Fe/Al₂O₃ and Fe–Co/Al₂O₃ catalysts. The carbon deposit was found by TEM analysis to be rich in carbon nanotubes in the case of Co/Al₂O₃ but to be very poor in the case of the Fe–Co/Al₂O₃ catalysts. The catalysts were characterized by TEM, XRD, and nitrogen adsorption. It was shown that iron and cobalt are in oxide form. Metal–support interactions and metal oxide particle size are influenced by the nature of the precursor and this nature is an important factor for the activity and selectivity of the catalysts. Moreover, a correlation has been found between the metal oxide particle sizes, the diameter of the carbon nanotubes, and the catalytic activity.

Keywords: Carbon nanotubes; Sol–gel; Metal precursors; Ethylene; Chemical catalytic vapour deposition

Ru-Sn catalysts for selective hydrogenation of crotonaldehyde: Effect of the Sn/(Ru+Sn) ratio by B.A. Riguetto; C.E.C. Rodrigues; M.A. Morales; E. Baggio-Saitovitch; L. Gengembre; E. Payen; C.M.P. Marques; J.M.C. Bueno (pp. 70-78).

One series of Ru-Sn/SiO₂ catalysts with various Sn loading was studied in the hydrogenation of crotonaldehyde. The addition of a small amount of Sn (1wt.% Sn) made the catalyst active for hydrogenation of both the CC and CO bonds. The enhancement of the surface electron density of the Ru particle is crucial to improving the adsorption and reactivity of the CO bond.▪The effects of the Sn/(Ru+Sn) ratio and Ru loading on the properties of silica-supported RuSn catalysts were investigated. Ru-Sn/SiO₂ bimetallic catalysts were prepared by the impregnation method and characterized in situ by XPS and Mössbauer spectroscopy. The XPS results indicated the presence of two Sn species on the surface of the catalysts, in different oxidation states—Sn⁰ and Sn n⁺, and¹¹⁹Sn Mössbauer spectra revealed Sn(II), Sn(IV), and intermetallic particles with structures such Ru₃Sn₇ I, Ru₃Sn₇ II, and oxide species (RuOSn). The contents of the various species depended on Sn loading. The reaction data showed that the Ru/SiO₂ catalyst was active only for hydrogenation of the CC bond, while the addition of a small amount of Sn (1wt.% of Sn) made the catalyst active for hydrogenation of both the CC and CO bonds. Upon increasing the Sn loading from 1 to around 3.6wt.%, the specific rate for CC hydrogenation is greatly reduced whereas the specific rate for CO hydrogenation decreases more gradually. The activity for CC hydrogenation remains unvarying for Sn loading higher than around 3.6wt.%. This results in an optimum selectivity to crotyl alcohol at Sn/(Ru+Sn) molar ratio around 0.2–0.3. The abrupt change of activity toward CO hydrogenation is observed as a lower binding energy than expected is observed for the Ru⁰. This enhancement of the surface electron density of the Ru particle is crucial to improving the adsorption and reactivity of the CO bond, but has the opposite effect on hydrogenation of the CC bond. The geometric effect of formation of Sn-Ru intermetallic and SnO_x compounds on the Ru particle surface may play a part in the suppression of CC bond hydrogenation.

Keywords: Ruthenium tin catalysts; SiO; ₂; Crotonaldehyde hydrogenation; XPS; Mössbauer spectroscopy

Kinetic study of the catalytic reforming of CH₄ with CO₂ to syngas over Ni/α-Al₂O₃ catalyst: The effect of temperature on the reforming mechanism by Yuehua Cui; Huidong Zhang; Hengyong Xu; Wenzhao Li (pp. 79-88).

The mechanism of the dry reforming over the Ni/α-Al₂O₃ catalyst remained constant in 550–575°C and 650–750°C but varied with temperature in 575–650°C. CH₄ dissociation was the rate-determining step (RDS) and CO desorption also restrained the dry reforming in 550–575°C. The reaction between CH_x and CO₂ became the RDS in 650–750 °C.▪The mechanism and the rate-determining steps (RDS) of CO₂ reforming of CH₄ were investigated over the typical Ni/α-Al₂O₃ catalyst in a wide temperature range of 550–750°C using steady-state and transient kinetic methods. After elimination of the effects of side reactions, the reforming reaction was controlled by kinetics. The activation energies of the reforming reaction and the reaction orders of CH₄, CO₂, H₂, and CO showed that the reforming reaction could be divided into three regions: 550–575°C, 575–650°C, and 650–750°C. The reaction rate was constant in the low and high temperature ranges but was varied with temperature in the middle range. The CH₄ dissociation reached equilibrium with Ni–H species above 650°C. The surface oxygen species originating from CO₂ became removable and reacted with CH_x species above 575°C. The reaction of CH_x with CO₂ was slower than that of CH₄ dissociation above 650°C, leading to the durative carbon deposition on the catalyst. CO competed with CH₄ on the Ni active sites below 650°C but was desorbed rapidly above 650°C. The formation of hydrogen is a rapid or equilibrium step in the reforming reaction. The CH₄ dissociation is the RDS and CO desorption also restrained the dry reforming in 550–575°C. The reaction between CH_x and CO₂ became the RDS in 650–750°C. And the restraining steps were switched from the former two steps to the latter step in 575–650°C. The reaction temperature remarkably influences the reforming mechanism through altering the reaction steps.

Keywords: Kinetic; Mechanism; Rate-determining step; Dry reforming; Ni/α-Al; ₂; O; ₃; CH; ₄; CO; ₂

Immobilization of copper Schiff base complexes in zeolite matrix: Preparation, characterization and catalytic study by Buddhadeb Dutta; Sreyashi Jana; Rajesh Bera; Pratap Kumar Saha; Subratanath Koner (pp. 89-94).

On immobilization in zeolite matrix the [Cu(NO₂-salen)(EtOH)] complex moiety showed a remarkable color change from green to gray. Spectroscopic analysis shows the complex moiety undergoes a severe distortion after immobilization. An excellent catalytic performance of the newly prepared hybrid catalysts was observed in oxidation of phenol and 1-naphthol. ▪New zeolite-immobilized hybrid catalysts Cu(NO₂-salen)–NaY have been prepared by encapsulating copper(II) Schiff base complexes [where NO₂-salenH₂ is N, N′-(ethylene)-bis-(5-nitro-salicylaldiimine)] in NaY zeolite matrix. The hybrid materials have been characterized by UV–vis, IR and EPR spectrometry and by X-ray powder diffraction analysis. The neat copper(II) Schiff base complex [Cu(NO₂-salen)(EtOH)] (1) has also been synthesized and characterized. A brilliant color change (green–gray) has been observed when the complexes are immobilized in zeolitic matrix. X-ray powder diffraction analysis of Cu(NO₂-salen)–NaY catalysts reveals that the structural integrity of the mother zeolite in the hybrid material remained intact upon immobilization of the complex. Spectroscopic studies indicate that coordination geometry of the complex undergoes a significant distortion when it is entrapped in the zeolite cavity. While Cu(NO₂-salen)–NaY catalysts showed moderate to excellent catalytic activity and product selectivity in the oxidation reactions, the pure complexes Cu(NO₂-salen) remained virtually catalytically inactive in these reactions. The efficiency of the catalysts depends on the stereo-electronic properties of the copper Schiff base moiety.

Keywords: Heterogeneous catalytic oxidation; Y-zeolite; Immobilization; Copper(II) Schiff base

Alkylation of bromobenzene with allyl acetate over zeolites: Influence of zeolite factors and reaction conditions on activity and selectivity by Kshudiram Mantri; Eileen Dejaegere; Gino V. Baron; Joeri F.M. Denayer (pp. 95-107).

The influence of zeolite factors such as pore geometry (viz. H-USY, H-BEA, H-MOR, H-ZSM-5) and Si/Al ratio and reaction conditions such as feed flow rate (liquid hourly space velocity, LHSV=57.6, 115, and 230h⁻¹), feed composition (molar ratio: allyl acetate/bromobenzene=1/10, 1/20, 1/40, 1/100, and 1/150) and reaction temperature (130, 150, and 170°C) in the alkylation of bromobenzene with allyl acetate has been investigated. The activity and selectivity in allyl acetate to alkylated products conversion are found to be strongly influenced by the zeolite factors. Catalysts with smaller pore sizes deactivate faster due to faster pore blocking by side products. H-USY zeolites deactivate the slowest and produce the largest amount of alkylation products. The distribution for the total alkylation products (consisting of allyl bromobenzene (ABB), cis- and trans-propenyl bromobenzene (PBB) and dialkylated product (DAP)) lies around 50% over the whole allyl acetate conversion range with H-USY. H-MOR and H-ZSM-5 produce practically no primary alkylation products, but rather a large amount of side products of the alkylating agent. The conversion of allyl acetate decreases with increasing liquid hourly space velocity and allyl acetate concentration in the feed. At high concentration of allyl acetate, the formation of light components is high. Higher reactor temperatures lead to higher initial catalyst activity, but also faster deactivation and lower selectivity for alkylation products.

Keywords: Alkylation; Bromobenzene; Allyl acetate; Allyl bromobenzene; H-USY; H-BEA; H-MOR; H-ZSM-5

Catalytic conversion of limonene over acid activated Serra de Dentro (SD) bentonite by C. Fernandes; C. Catrinescu; P. Castilho; P.A. Russo; M.R. Carrott; C. Breen (pp. 108-120).

A series of acid-activated clay catalysts were prepared from a purified bentonite, rich in structural iron, collected at Serra de Dentro on the island of Porto Santo. The purified bentonite exhibited a surface area of 130m²g⁻¹ which increased to values as high as 500m²g⁻¹ following activation with 4M HCl at 95°C for 30min (SD-4M-95-30). The ability of the activated samples to convert limonene to p-cymene was evaluated using a reaction time of 15min at 80°C. The sample prepared using 3M HCl at 95°C for 30min (SD-3M-95-30) offered the optimum combination of surface area (470m²g⁻¹) and acidity (0.26mmolg⁻¹) and 95% of the limonene was converted to product. About 15% of the product mixture was p-cymene whilst non-volatile products and polymeric species made up 54% of the product mixture. The presence of iron in the octahedral sheet of the SD bentonite appears responsible for the dehydrogenation activity. TG–MS analysis of acid activated samples, saturated with cyclohexylamine, reflected the dehydrogenation capabilities of the catalysts in that SD-3M-95-30 produced the most benzene and aniline as decomposition/transformation products.A series of acid-activated clay catalysts were prepared from a purified bentonite, rich in structural iron, collected at Serra de Dentro on the island of Porto Santo. The ability of the activated samples to convert limonene to p-cymene was evaluated. TG–MS analysis of acid activated samples, saturated with cyclohexylamine, reflected the dehydrogenation capabilities of the catalysts. ▪

Keywords: Acid activated clays; Acidity; Catalysis; Limonene; p; -Cymene

Steam reforming of methanol using supported Mo₂C catalysts by Sean S.-Y. Lin; William J. Thomson; Timothy J. Hagensen; Su Y. Ha (pp. 121-127).

Mo₂C supported on zirconia has shown the potential to be a promising reforming catalyst to produce hydrogen from methanol. At 400°C with a steam-to-carbon ratio of one, 97% of methanol conversion and 62% of hydrogen yield can be achieved by using supported Mo₂C/ZrO₂ catalyst. The hydrogen production rate is 20μmol/gs at WHSV of 3h⁻¹. ▪Two supported molybdenum carbide catalysts, Mo₂C supported on γ-alumina (Mo₂C/γ-Al₂O₃) and zirconia (Mo₂C/ZrO₂), were investigated as an alternative catalyst for steam reforming of methanol. The catalysts were prepared by a temperature-programmed reaction (TPR) method, and it was found that the supported Mo₂C catalysts are superior to an unsupported catalyst, with Mo₂C/ZrO₂ having a higher hydrogen yield than Mo₂C/γ-Al₂O₃. We hypothesize that the suppression of methanation by interaction between molybdenum carbide and the zirconia support resulted in the increased hydrogen yield. Results from diffuse-reflectance infrared spectroscopy (DRIFTS) suggested that the ability of the zirconia support to retain methoxy groups while resisting the formation of hydroxyl groups on its surface is a key factor leading to a molybdenum carbide/zirconia support interaction which suppresses methanation. Under the operating conditions of a steam-to-carbon ratio of 1 and 400°C, the reforming activity of the Mo₂C/ZrO₂ catalyst remained stable for longer than 10h.

Keywords: Supported molybdenum carbide; Methanol steam reforming; TPR method; Methanation; Water–gas shift reaction; Hydrogen yield

Chromium-containing small pore mesoporous silicas: Synthesis, characterization and catalytic behavior in the liquid phase oxidation of cyclohexane by S. Shylesh; Prinson P. Samuel; A.P. Singh (pp. 128-136).

Organic–inorganic hybrid mesoporous silica materials containing chromium and various organo trialkoxysilanes (chloropropyl, vinyl, methyl) were prepared by the co-condensation method, in presence of cetyl trimethyl ammonium surfactants. Small pore chromium-silica samples having pores in the supermicroporous region can be prepared from the large pore hybrid mesoporous chromium samples by simple calcination, without changing the chain length of the surfactant used in the assembly process.▪Organic–inorganic hybrid mesoporous silica materials containing chromium and various organo trialkoxysilanes (chloropropyl, vinyl, methyl) were prepared by the co-condensation method, in the presence of cetyl trimethyl ammonium surfactants. The hybrid material, containing chromium, retains one X-ray diffractogram (XRD) peak up to a molar ratio of 1:1 between tetra ethyl orthosilicate (TEOS) and organosilane in the synthesis gel. Small pore mesoporous chromium-silica samples can be prepared from the large pore hybrid mesoporous chromium samples by calcination. By this method, the pore size of the material can be tailored into the supermicroporous region, without changing the chain length of the surfactant used in the assembly process, as judged from the XRD and N₂ sorption isotherms. The shrinkage in pore size is dependent on the nature and percentage of the organic pendant groups, such that the chloro propyl and vinyl pendant mesoporous material show more pore size shrinkage than the smaller methyl pendant units. Because of the tailorable pore size and with better textural characteristics, the chromium samples show better catalytic activity in the aerial oxidation reaction of cyclohexane than the conventional chromium-containing mesoporous material, like Cr-MCM-41, under a solvent free system. Among the porous chromium catalysts, the samples prepared using chloro propyl silane show higher cyclohexane conversion and cyclohexanone selectivity and behave as a true heterogeneous catalyst.

Keywords: Small pore silicas; Chromium; Cyclohexane; Oxidation

Structure characterization of orthorhombic phase in MoVTeNbO catalyst by powder X-ray diffraction and XANES by H. Murayama; D. Vitry; W. Ueda; G. Fuchs; M. Anne; J.L. Dubois (pp. 137-142).

Pure orthorhombic phase of MoVTeNbO catalyst prepared by hydrothermal method was characterized by combination of XANES and XRD. The unit cell is Pba2 with a=2.1116nm, b=2.6594nm, c=0.4007nm. The unit formula is Mo_0.55⁵⁺Mo_6.76⁶⁺V_1.52⁴⁺V_0.17⁵⁺Te_0.69⁴⁺Nb_1.00⁵⁺O_x²⁻ (28.34< x<28.69). The analysis refined geometric arrangement of the catalyst, particularly the positions, fractional occupancies, and oxidation states of metal atoms. ▪The structure of the pure orthorhombic phase of the MoVTeNbO catalyst used for propane selective oxidation to acrylic acid was characterized by a combination of XANES and XRD. The vanadium K absorption pre-edge peak position due to 1s–3d transition obtained by XANES shows that average oxidation state of V is 4.1+. The Rietveld XRD analysis refined the unit cell parameters, chemical formula, and geometric arrangement of the catalyst, particularly the positions and fractional occupancies of metal atoms. The unit cell is Pba2 with a=2.1116nm, b=2.6594nm, c=0.4007nm. The unit formula is Mo_0.55⁵⁺Mo_6.76⁶⁺V_1.52⁴⁺V_0.17⁵⁺Te_0.69⁴⁺Nb_1.00⁵⁺O_x²⁻ (28.34< x<28.69). The structure refinement of five-, six-, and seven-membered rings of MO₆ (M=Mo or V) determined that Nb⁵⁺ is localized in the pentagonal channel surrounded by MO₆ octahedra, that Te⁴⁺ is localized in the hexagonal channel surrounded by MO₆, and that the heptagonal channel is not occupied. Results revealed that Te⁴⁺ is only localized in the hexagonal channel at 70% occupancy. Te in the catalyst proves to be highly stable.

Keywords: MoVTeNbO mixed oxide catalyst; XRD; XANES; Rietveld refinement; Propane selective oxidation

Partial oxidation of propane to synthesis gas over noble metals-promoted Ni/Mg(Al)O catalysts—High activity of Ru–Ni/Mg(Al)O catalyst by Masato Shiraga; Dalin Li; Ikuo Atake; Tetsuya Shishido; Yasunori Oumi; Tsuneji Sano; Katsuomi Takehira (pp. 143-154).

Ru–Ni_0.5/Mg_2.5(Al)O bimetallic catalysts prepared by adopting “memory effect” of hydrotalcite showed high and stable activity in the partial oxidation of propane to synthesis gas; the deactivation due to both Ni oxidation and coke formation on the catalyst was effectively suppressed by the loading of 0.1wt%Ru. ▪Effect of the addition of small amount of noble metal, i.e. Ru, Rh, Pd, Ir or Pt, in the Ni/Mg(Al)O catalyst on the catalytic activity for the partial oxidation of propane has been investigated. Mg_2.5(Ni_0.5)–Al hydrotalcite was prepared by co-precipitation and was calcined to form Mg_2.5(Al,Ni_0.5)O periclase. When the powders of the periclase were dipped in an aqueous solution of the nitrate of Ru(III), Rh(III), Pd(II), Ir(III) or Pt(II), a reconstitution of the hydrotaclite took place on the surface of Mg_2.5(Al,Ni_0.5)O particles due to a “memory effect”. The calcination followed by the reduction of the dipped samples produced highly dispersed noble metal-Ni supported catalysts. The loading of noble metal gave rise to a decrease in the reduction temperature of Ni²⁺ to Ni⁰ on Mg_2.5(Al,Ni_0.5)O periclase, an increase in the amount of H₂ uptake on the Ni metal and moreover a decrease in the particle size of Ni metal formed on the noble metals-Ni/Mg_2.5(Al)O catalyst. When the noble metals-Ni_0.5/Mg_2.5(Al)O catalysts were tested in the temperature-cycled operation of propane partial oxidation between 400 and 700°C, the deactivation due to both Ni oxidation and coke formation on the catalyst was effectively suppressed by the loading of noble metals. The combination of Ru and Ni_0.5/Mg_2.5(Al)O was the most effective; the high sustainability against both Ni oxidation and coke formation was obtained only with 0.1wt% of Ru loading. A dipping of 1.0g of the powders of Ni_0.5/Mg_2.5(Al)O periclase in a 5ml of Ru(III) nitrate-aqueous solution was enough to reconstitute the hydrotalcite on the surface of the powder particles, leading to the formation of the Ru–Ni bimetal loaded catalyst with the high activity as well as the high sustainability.

Keywords: Propane partial oxidation; H; ₂; production; Ru–Ni/Mg(Al)O catalyst; Memory effect; Hydrotalcite

Coke formation on WO₃/SiO₂ metathesis catalysts by D.J. Moodley; C. van Schalkwyk; A. Spamer; J.M. Botha; A.K. Datye (pp. 155-159).

An appreciable amount of coke (49wt%) forms over an 8wt% WO₃/SiO₂ catalyst during the metathesis of 1-alkenes to internal alkenes. Catalyst activity is maintained despite these high coke levels. To understand this phenomenon, the coked catalyst was characterized by energy filtered transmission electron microscopy (EFTEM). Trace amounts of oxygenated compounds were shown to dramatically reduce coke levels. ▪An appreciable amount of coke forms over an 8wt% WO₃/SiO₂ during the metathesis of 1-alkenes to internal alkenes. Catalyst activity is maintained despite the high coke levels (49wt%). To understand this phenomenon, the coked catalyst was characterized by thermogravimetric analysis (TGA), BET and energy filtered transmission electron microscopy (EFTEM). Even at high coke levels, carbon maps show that the coke is dispersed over the support rather than covering the tungsten oxide. This observation may explain why the high activity of the catalyst is maintained and gives an indication that the location of coke laydown is more important than the amount deposited, in determining catalyst activity. Trace quantities of water, butanol and 2-pentanone were introduced into the feed stream and this resulted in the inhibition of coke formation without a significant loss in catalyst activity. 2-Pentanone was found to be the most effective inhibitor. Coking profiles indicated that the internal alkenes coked more rapidly than the 1-alkene feed.

Keywords: Tungsten oxide; Coke formation; Alkene metathesis; EFTEM

Catalytic vapour phase epoxidation of propene with nitrous oxide as an oxidant by Thomas Thömmes; Sebastian Zürcher; Andrea Wix; Andreas Reitzmann; Bettina Kraushaar-Czarnetzki (pp. 160-169).

The vapour phase epoxidation of propene with nitrous oxide (N₂O) was experimentally investigated in a fixed bed reactor using a CsO_x/FeO_y/SiO₂ catalyst in a broad range of residence times. A complex reaction network was derived from the trends of product selectivities as function of the conversion. For the determination of the reaction paths, not only propene but also its oxidation products, propylene oxide (PO) and propionaldehyde (PA), were used as reactants. The selectivity to PO was found to be limited due to fast side reactions, like PO isomerisation reactions and, in particular, the formation of higher molecular weight products (HMP) mainly present as carbonaceous deposits (coke) on the catalyst. The amount of HMP and coke was quantified through several methods and both were identified as the major byproducts. Although PO is formed with more than 60% selectivity among the directly identified vapour phase products, the maximum selectivity is only about 30% when taking the HMP into account.A complex reaction network was derived from experiments using propene, propylene oxide (PO), and propionaldehyde as reactants. Fast side reactions, especially to higher molecular weight products (HMP) limit the selectivity to PO. Although PO is formed with more than 60% selectivity among the directly identified vapour phase products, the maximum selectivity is only about 30% when taking the HMP into account.▪

Keywords: Reaction engineering; Partial oxidation; Propylene oxide; Propionaldehyde; Iron oxide; Silica gel; Reaction network; Carbon balance; Coke

Design of nanostructured multifunctional Pd-based catalysts from layered double hydroxides precursors by Didier Tichit; María de Jesús Martínez Ortiz; Denisa Francová; Corine Gérardin; Bernard Coq; Robert Durand; Federica Prinetto; Giovanna Ghiotti (pp. 170-177).

Three types of multifunctional supported Pd catalysts have been obtained from LDH precursors by: impregnation, coprecipitation and synthesis of a Pd colloid Mg/Al LDH nanocomposite, respectively. That prepared from the nanocomposite precursor ensures the best balance equilibrium between the different functions and leads to the higher performances in the one-pot synthesis of 2-methyl-3-phenyl-propanal (MPPAL) from benzaldehyde and propanal. ▪Three types of multifunctional supported Pd catalysts (0.2wt.% Pd) have been obtained from layered double hydroxides (LDH) precursors by: (i) impregnation with Pd(acac)₂ of a Mg(Al)O support, (ii) coprecipitation of a multicationic Pd/Mg/Al LDH, and (iii) synthesis of a Pd colloid Mg/Al LDH nanocomposite. The precursors have then been calcined at 773K and reduced at 523K to obtain the catalysts, which exhibit very different basic properties and Pd particle size distributions. Their potential was evaluated in the one-pot synthesis of 2-methyl-3-phenyl-propanal (MPPAL) from benzaldehyde and propanal. The full one-pot synthesis of MPPAL was performed sequentially operating in two stages, i.e. for 20h in N₂, then for 7h in H₂ atmospheres. The activities of the catalysts in the first stage of the reaction (condensation and dehydration steps) are related to their reconstruction ability in the propanol/water solvent to give Brønsted basic sites. The hydrogenation ability of the catalysts decreases when the average Pd⁰ particle size decreases. The specific behavior of the nanosized particles accounts for a decrease of the adsorption strength of CC bond due to the enhancement of the metal–support interaction. The catalyst prepared from a Pd nanocomposite precursor ensures the best balance between the different functions. It leads to a MPPAL selectivity of 77% at 64% benzaldehyde conversion. Benzyl alcohol formed by hydrogenation of benzaldehyde on Pd and hydrogen transfer from propanol is the main secondary product. However, the process is negatively affected by the high consumption of propanal from self-condensation.

Keywords: One-pot reactions; Benzaldehyde; Propanal; Layered double hydroxides; Palladium; Nanocomposites

Migration and oxidation of tungsten species at the origin of acidity and catalytic activity on WO₃-ZrO₂ catalysts by M.A. Cortés-Jácome; C. Angeles-Chavez; E. López-Salinas; J. Navarrete; P. Toribio; J.A. Toledo (pp. 178-189).

Tungsten atoms are initially in strong interaction with the ZrO₂ in a reduced W⁵⁺ oxidation state. As temperature increases from 560 to 800°C, W atoms are expelled to the surface of ZrO₂ forming WO_x nanoclusters of ≤0.5nm and showing high acid sites density, but poor catalytic activity. When these nanoclusters grow to ca. 3.0nm WO_x domains, acid sites decreased whereas catalytic activity increased. ▪A WO₃-ZrO₂ catalyst, prepared by a precipitation method, was annealed at 560, 700 and 800°C with a view to examine the nature of WO_x species using infrared and Raman spectroscopy, X-ray photoelectron spectroscopies (XPS), high resolution and energy filtered transmission electron microscopy (HRTEM and EFTEM). When calcining at 560°C, a large amount of W atoms remain in W⁵⁺ oxidation state, in strong interaction with the ZrO₂, forming ZrOW bonds. Only a little fraction of the W atoms was expelled to the surface as isolated WO_x species, which are responsible for the Brönsted acid sites. After calcining at 700°C, all W atoms migrated to the surface, remaining in full W⁶⁺ oxidation state, forming ca. 0.5nm nanoclusters. In these nanoclusters, all W atoms are exposed on the surface and promote acid sites, mainly Brönsted acidity. When the sample was calcined at 800°C, the tungsten nanoclusters grew to partially reduced ca. 3.0nm WO_x domains. These WO_x domains showed very low acid sites density and strength, however, they showed the highest catalytic activity in n-hexane isomerization reaction; supporting the hypothesis that redox properties of WO_x domains are responsible for this reaction.

Keywords: Tungstated zirconia; XPS spectroscopy; Brönsted acid sites; FT-IR; Raman; n; -Hexane isomerization; HRTEM; EFTEM

Deactivation of nitrile hydrogenation catalysts: New mechanistic insight from a nylon recycle process by Michael W. Duch; Alan M. Allgeier (pp. 190-198).

In the recycling of nylon polymer, ammonolysis and subsequent nitrile hydrogenation leads to reversion of polymers to monomer units. The use of certain Raney^® catalysts in the hydrogenation step results in deactivation by a different mechanism than that previously reported for acetonitrile hydrogenation. The process and catalysts are characterized and improved reactivity for Raney^® Co over Raney^® Ni is documented. ▪In the recycling of nylon-6 and nylon-6,6, high temperature ammonolysis leads to reversion of the polymers to monomer units and dehydration of amide monomers to nitrile molecules. The resulting product is a mixture of 6-aminocapronitrile, caprolactam, adiponitrile, hexamethylenediamine and other species. To complete the recycle loop the nitrile molecule can be hydrogenated to hexamethylenediamine. This liquid phase hydrogenation has been studied over Raney^® Ni and Raney^® Co catalysts at less than 100°C and 3.5MPa in semi-batch mode. Raney^® Ni exhibited rapid deactivation in the absence of sodium hydroxide, while Raney^® Co provided long catalyst life. In comparison studies, Raney^® Ni also deactivated during hydrogenation of pure adiponitrile, in the absence of sodium hydroxide. While sodium hydroxide inhibits Raney^® Ni deactivation, it presents an economic and environmental challenge for waste handling. Analysis of recovered catalyst samples by ESCA showed an increase in nitrogen and carbon on the surface of deactivated Raney^® Ni samples compared to recovered Raney^® Co and control samples. The observed overlayer was consistent with the formation of oligomeric secondary amines, which covered the catalyst surface and prevented further reaction. Amine coupling reactions were favored for Raney^® Ni compared to Raney^® Co.

Keywords: Deactivation; Raney; Nitrile hydrogenation; Nylon; Recycle; Polyamine; Hexamethylenediamine; Adiponitrile; Caprolactam; Ammonolysis

Fluidizable reforming catalyst development for conditioning biomass-derived syngas by Kimberly A. Magrini-Bair; Stefan Czernik; Richard French; Yves O. Parent; Esteban Chornet; David C. Dayton; Calvin Feik; Richard Bain (pp. 199-206).

A multi-stage catalyst development approach is used to evaluate and optimize fluidizable tar reforming catalysts for conditioning syngas from biomass gasification. Catalyst performance was evaluated at micro through pilot scales and a 60kg batch of the best catalyst evaluated in a pilot-scale reformer. Temperature-programmed reduction is a sensitive probe of Ni species in new and used catalysts. ▪A multi-stage catalyst development approach is used to evaluate and optimize fluidizable tar reforming catalysts for conditioning syngas from biomass gasification. Previous work showed that catalyst fluidization is required to efficiently reform biomass-derived pyrolysis oil and its fractions to syngas as fluidization optimizes contact between catalyst particles and feedstocks while reducing coke formation. Biomass-derived tars like pyrolysis oils are also complex, largely aromatic feedstocks that require fluidization to improve reforming efficiency. Because industrial reforming catalysts are designed for fixed-bed operations and not for fluidized processing, attrition resistant supports and catalysts required development. We identified and tested particulate aluminas for attrition resistance under fluidized steam reforming conditions and prepared nickel-based catalysts from the strongest supports. The performance of these catalysts was tested in a microactivity test system (MATS), which used 1g catalyst quantities, had high throughput, and measured oxidation, reduction and model tar compound steam reforming. Promising candidates from MATS screening were next evaluated in a laboratory-scale fluidized bed reactor with 250g of catalyst using more realistic flow conditions and input streams. A 60kg batch of the best catalyst identified in the laboratory fluid bed was then prepared and evaluated for biomass-derived syngas conditioning in a pilot-scale reformer. Fresh and used catalysts were characterized with scanning electron, energy dispersive X-ray, and inductively coupled plasma spectroscopies. The most active and attrition resistant catalyst identified through multi-stage testing contains nickel, magnesium and potassium on 90% alpha alumina particles of 100–400μm size.

Keywords: Biomass gasification; Fluidizable reforming catalysts

The effect of support on methane activation over Pt catalysts in the presence of MoO₃ by Ruth L. Martins; Maria A.S. Baldanza; Mariana M.V.M. Souza; Martin Schmal (pp. 207-212).

We reported the role of different supports (silica, alumina and zirconia) on non-oxidative conversion of methane, through the isothermal two-step reaction, on Pt-loaded catalysts, with or without the presence of MoO₃. The activated chemisorption of methane, followed by reaction of the carbon adspecies with hydrogen was conducted in pulse and continuous modes, in the temperature range of 473–673K.▪It is reported the role of different supports (silica, alumina and zirconia) on the non-oxidative conversion of methane, through the isothermal two-step reaction, on Pt-loaded catalysts, with or without the presence of MoO₃. The activated chemisorption of methane, followed by reaction of the carbon adspecies with hydrogen was conducted in pulse and continuous modes, in the temperature range of 473–673K. It was observed by using pulse mode that evolutions of H₂, CO and CO₂ occurred simultaneously with the pulses of methane without the formation of higher hydrocarbons. The reactivity, regarding the CH₄ conversion, with or without MoO₃, follows the sequence Pt/Al₂O₃≈Pt/ZrO₂>Pt/SiO₂. Also the hydrogenation of carbon residues produced only methane. The presence of MoO₃ had a positive influence concerning the reactivity of carbon residues, on zirconia and especially on alumina supported catalysts. In the flow mode operation, methane chemisorption is followed by the evolution of H₂, plusC2, C₂,C3=, and C₃, depending on the nature of the support. The hydrogenation of carbon residues produced mainly methane, but ethane and propane were also detected specially in the presence of MoO₃ which improves the mobility of CH_X adspecies, favoring the CC nucleation.

Keywords: Methane activation; Supported transition metal catalysts; Hydrogenation of surface carbon adspecies

Alumina-catalyzed epoxidation of unsaturated fatty esters with hydrogen peroxide by Jorge Sepulveda; Sergio Teixeira; Ulf Schuchardt (pp. 213-217).

Two commercial aluminas and one produced by the sol–gel process were compared for the epoxidation of unsaturated fatty esters using anhydrous or aqueous hydrogen peroxide as oxidant and ethyl acetate as solvent. The aluminas show a high catalytic activity and very good selectivity towards the epoxides. The sol–gel alumina was more efficient and when using aqueous hydrogen peroxide could be recycled several times without loss of activity.▪Two commercial aluminas and one produced by the sol–gel process were compared for the epoxidation of unsaturated fatty esters using anhydrous or aqueous hydrogen peroxide as oxidant and ethyl acetate as solvent. The aluminas show a good catalytic activity and excellent selectivity towards the epoxides. The sol–gel alumina was more efficient and when using aqueous hydrogen peroxide could be recycled several times.

Keywords: Epoxidation; Methyl oleate; Alumina; Hydrogen peroxide; Vegetable oils

Highly efficient conversion of aldehydes to geminal diacetates (solvent-free) and their deprotection using facile and reusable molybdenum and tungsten polyoxometalates by Razieh Fazaeli; Shahram Tangestaninejad; Hamid Aliyan (pp. 218-226).

Keggin-type supported polyoxometalates (supported-H₃PW₁₂O₄₀ and H₃PMo₁₂O₄₀) were found to be efficient catalysts for preparation of 1,1-diacetates under solvent-free conditions. Deprotection of the resulting 1,1-diacetates were achieved using the same catalysts in acetonitrile solvent. This new method consistently has the advantage of excellent yields and short reaction times. Further, the catalysts can be reused for several times but they will be less active.

Keywords: 1,1-Diacetates (acylals); Supported catalysts; Polyoxometalates (POMs); Heteropolyacids (HPAs); Keggin-type polyoxometalates; Solvent-free reaction

Catalytic reactions of methylcyclohexane (MCH), on partially reduced tungsten oxide(s) by H. Belatel; H. Al-Kandari; F. Al-Kharafi; F. Garin; A. Katrib (pp. 227-233).

In situ XPS–UPS characterization of bulk WO₃ defines the reduction conditions to obtain different W₂O₅ and WO₂ phases. UPS enabled us to clearly define the presence of WO₂. The presence of both, Brönsted and metal functions in WO₂(H_x)_ac explains the catalytic behaviour of the sample towards the isomerization–dehydrogenation of methylcyclohexane. ▪ Figure: UPS of WO₃ following reduction by H₂: (a) as received and (b) 773K for 2h.In situ XPS–UPS characterization of the reduction processes of bulk WO₃ following the exposure of the sample to hydrogen at different temperatures up to 773K enabled us to define the reduction conditions at which each of the different W₂O₅ and WO₂ phases could be obtained. The reduction process takes place in the upper 10–15 atomic layers, most probably in a sandwich like atomic layer superposition structure of different tungsten oxide(s) at each set of reduction conditions. In order to define the nature of the chemical composition of the outermost surface layer; responsible for the chemical activity, the combination of XPS–UPS techniques proved to be valuable. The depth detection limit and relatively high collision cross section in the low binding energy valence electrons of UPS enabled us to clearly define the presence of WO₂, with the bifunctional WO₂(H_x)_ac structure on its surface at reduction temperatures above 673K. The presence of both, Brönsted and metal functions on the same surface of WO₂(H_x)_ac explains the catalytic behaviour of the sample towards the isomerization–dehydrogenation of methylcyclohexane.

Keywords: Methylcyclohexane; Isomerization; Dehydrogenation; Tungsten trioxide; Tungsten dioxide; XPS; UPS

Iron and copper oxide modified SBA-15 materials as catalysts in methanol decomposition: Effect of copolymer template removal by Tanya Tsoncheva; Jessica Rosenholm; Mika Linden; Lyubomira Ivanova; Christo Minchev (pp. 234-243).

The initial state of iron and copper oxide species and their reductive and catalytic properties in the SBA-15 host matrix is influenced by the presence of the silica walls microporosity, tailored by the method of tri-block copolymer template removal. These effects depend on the nature of the loaded metal oxide. ▪Several SBA-15 type mesoporous silicas, where different means of surfactant removal have been used, have been modified by copper and iron oxide, and tested as catalyst for methanol decomposition. The materials were thoroughly characterized by nitrogen physisorption, X-ray diffraction, Moessbauer spectroscopy and temperature programmed reduction with hydrogen. The different means of template removal results in SBA-15 materials different in mesopore size and degree of microporosity. These parameters have a strong influence on the reductive and catalytic properties of the obtained composite materials.

Keywords: Copper and iron oxide modified SBA-15; Template removal; Methanol decomposition

Development of a Ru/C catalyst for glycerol hydrogenolysis in combination with an ion-exchange resin by Tomohisa Miyazawa; Shuichi Koso; Kimio Kunimori; Keiichi Tomishige (pp. 244-251).

Ru/C catalysts prepared from Ru(NO)(NO₃)₃ and active carbon with a low surface area (∼250m²/g) exhibited higher activity and selectivity in the glycerol conversion to propanediols than commercially available Ru/C catalysts (Ru/C^*) in combination with an ion-exchange resin. Characterization results suggested highly dispersed Ru metal particles on the graphite phase can be effective. ▪The combination of Ru/C and Amberlyst ion-exchange resin is effective for the dehydration and hydrogenation (denoted as hydrogenolysis) of glycerol to 1,2-propanediol under mild reaction conditions (393K). A Ru/C catalyst prepared by using active carbon with a low surface area (∼250m²/g) showed better performance than that prepared by using active carbon with a high surface area. In addition, treatment of Ru/C catalysts prepared from Ru(NO)(NO₃)₃ with Ar flowing at the appropriate temperature enhanced the performance compared to that of the commercially available Ru/C catalysts. This temperature treatment can be influenced by the decomposition of Ru precursor salt and aggregation of Ru metal particles. In addition, the degradation reaction as a side-reaction to C1 and C2 compounds of glycerol hydrogenolysis was more structure-sensitive than the hydrogenolysis reaction, and the selectivity of hydrogenolysis was lower on smaller Ru particles. The combination of Ru/C with the Amberlyst resin enhanced the turnover frequency of 1,2-propanediol formation drastically, and this indicates that 1,2-propanediol can be formed mainly by dehydration of glycerol to acetol catalyzed by Amberlyst and subsequent hydrogenation of acetol to 1,2-propanediol catalyzed by Ru/C.

Keywords: Glycerol; Hydrogenolysis; Ruthenium; Ion-exchange resin; Propanediol

Surface modification of Ni catalysts with trace Pd and Rh for oxidative steam reforming of methane by Yuya Mukainakano; Baitao Li; Shigeru Kado; Tomohisa Miyazawa; Kazu Okumura; Toshihiro Miyao; Shuichi Naito; Kimio Kunimori; Keiichi Tomishige (pp. 252-264).

Surface modification of Ni with trace Pd by a sequential impregnation method (Pd/Ni) was more effective for the suppression of hot-spot formation during oxidative steam reforming of methane than that by a co-impregnation method (Pd+Ni), and the formation of surface Pd–Ni alloy is suggested by EXAFS and TPR. The effect of surface modification with Rh was also investigated. ▪Bimetallic catalysts (Pd–Ni and Rh–Ni) were prepared by co-impregnation and sequential impregnation methods to investigate catalytic performance in oxidative steam reforming of methane. These bimetallic catalysts gave high methane conversion even at low W/ F such as 0.07gh/mol. The thermographical observation 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. In particular, Pd–Ni catalysts prepared by the sequential impregnation method showed higher resistance to hot-spot formation than monometallic Pd and Ni catalysts, and this can be a synergetic effect of Pd and Ni. Temperature-programmed reduction (TPR) with H₂ revealed that the addition of Pd or Rh by a sequential impregnation method greatly promoted the reduction of Ni species. Extended X-ray absorption fine structure (EXAFS) analysis confirmed the formation of Pd–Ni alloy and the preferential location of Pd atoms on the surface of the bimetallic particles over the Pd/Ni catalysts. Surface modification of Ni with Pd by sequential impregnation is effective for promotion of the activity and suppression of hot-spot formation.

Keywords: Oxidative steam reforming of methane; Pd; Rh; Ni; Thermography; Hot spot; Surface segregation

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Applied Catalysis A, General (v.318, #)