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Applied Catalysis A, General (v.283, #1-2)
Novel tungsten-containing mesoporous HMS material: its synthesis, characterization and catalytic application in the selective oxidation of cyclopentene to glutaraldehyde by aqueous H2O2 by Xin-Li Yang; Wei-Lin Dai; Hui Chen; Jian-Hua Xu; Yong Cao; Hexing Li; Kangnian Fan (pp. 1-8).
Tungsten-containing hexagonal mesoporous silica (HMS) has been synthesized by using dodecylamine as template at room temperature. The as-prepared novel material is very active as a catalyst for the selective oxidation of cyclopentene (CPE) to glutaraldehyde (GA) with environmentally benign hydrogen peroxide as the oxidant. Tungsten species could stably exist in the silica-based matrix of HMS up to a Si/W molar ratio of 30, as determined by X-ray diffraction (XRD), laser Raman spectroscopy, and FT-IR. Proper content of tungsten species and its high dispersion account for its high activity. Complete conversion of cyclopentene and very high yield of glutaraldehyde (∼76.3%) are obtained over the W-HMS catalyst with a Si/W molar ratio at 30. Furthermore, almost no tungsten species are leached into the reaction solution, enabling the catalyst to be employed for many reaction cycles without dramatic deactivation.
Keywords: Cyclopentene; Glutaraldehyde; H; 2; O; 2; Tungsten; HMS; W-HMS
Study of the reaction mechanisms between Pt(acac)2 and alumina surface sites by M. Womes; T. Cholley; F. Le Peltier; S. Morin; B. Didillon; N. Szydlowski-Schildknecht (pp. 9-22).
A new preparation technique is presented allowing the controlled variation of the average size of platinum particles in small steps of 0.2–0.5nm in the size range between 1 and 2nm. The particle growth is achieved by refilling, i.e. by increasing the metal loading of a parent catalyst in a separate preparation step. The technique makes use of the selective decomposition of a platinum complex, platinum bis-acetylacetonate, Pt(acac)2, on reduced platinum particles. Anchoring of the complex on the surface of the support and thus appearance of new small particles is completely avoided by appropriate surface treatments developed on the basis of a study of the reaction mechanisms between Pt(acac)2 and the support. Three types of surface sites could be identified in this study by their specific reactivity towards Pt(acac)2. A model is presented describing the nature of these sites, the occurrence of which is correlated with the degree of dehydroxylation of the alumina surface. The efficiency of the new technique in increasing the particle size while reducing to a minimum any broadening of the initial narrow size distribution is demonstrated. The results are discussed in terms of particle shapes and two- and three-dimensional growth mechanisms.
Keywords: Alumina surface sites; Alumina surface treatments; Infrared spectroscopy; Platinum particle growth; Platinum particle shape; Platinum particle size; Pt(acac); 2; Reaction mechanisms Pt(acac); 2; – alumina surfaces; Pt/Al; 2; O; 3; catalysts; Refilling
Effect of the metal precursor on the surface site distribution of Al2O3-supported Ru catalysts: catalytic effects on the n-butane/H2 test by A. Maroto-Valiente; M. Cerro-Alarcón; A. Guerrero-Ruiz; I. Rodríguez-Ramos (pp. 23-32).
Several alumina-supported Ru catalysts prepared from different metal precursors were comparatively studied by H2 and CO adsorption microcalorimetry and by Fourier transformed-infrared spectroscopy (FT-IR) of the chemisorbed CO molecule. The correlation of the results thus obtained from these techniques with those on the n-butane/H2 reaction test, provides useful information about the type and distribution of the surface active sites on the supported metal crystallites. Also, the comparison of the results obtained from these complementary techniques with those reported for monocrystals or from other studies available in the scientific literature for supported Ru catalysts, enables the tentative attribution of the type of exposed crystalline planes. In this way, the energetic distribution of surface sites has been shown to depend on the mean metal particle size as well as on the Ru precursor involved in the preparation.
Keywords: Alumina-supported metal catalysts; Ruthenium; Surface characterization; H; 2; adsorption; CO adsorption; Microcalorimetry; FT-IR of adsorbed CO; n; -Butane hydrogenolysis
Kinetics of the reaction of toluene with benzyl alcohol over a Nafion–silica composite by Paolo Beltrame; Giovanni Zuretti (pp. 33-38).
The title reaction, a set of concurrent–consecutive steps, was studied in a slurry batch reactor at 50, 65, and 75°C, using cyclohexane as solvent and Nafion SAC-13 as solid acid catalyst. The final products were found to be dibenzylether, the isomers of benzyltoluene and dibenzyltoluenes and small amounts of unidentified byproducts. The kinetic results were interpreted by a Langmuir–Hinshelwood model, evaluating the main kinetics and adsorption coefficient involved in the reactions and their temperature dependence.
Keywords: Activation energy; Adsorption enthalpy; Benzyltoluene; Langmuir–Hinshelwood model; Nafion–silica composite
Monolith loop catalytic membrane reactor for Fischer–Tropsch synthesis by Michael C.J. Bradford; Mure Te; Allen Pollack (pp. 39-46).
A monolith loop catalytic membrane reactor (ML-CMR) concept for Fischer–Tropsch synthesis (FTS) was investigated by evaluating the performance of a P/Pt–Co/γ-Al2O3 catalyst in a prototype, tubular CMR and in a tubular, fixed-bed reactor (FBR). Although experimental data demonstrate that the selectivity to paraffins and the product yield per unit catalyst mass exhibited by the P/Pt–Co/γ-Al2O3 catalyst in the tubular CMR exceed those observed by the same catalyst in a tubular FBR, simple model calculations indicate that the ML-CMR product yield per unit reactor volume, at its present stage of development, is less than that for state-of-the-art multi-tubular fixed-bed and slurry-bubble column reactors.
Keywords: Fischer–Tropsch; Monolith loop; Membrane reactor; Natural gas conversion
Novel tough catalyst supports for reactions involving HF by Yusaku Takita; Takeshi Ohkuma; Hiroyasu Nishiguchi; Katsutoshi Nagaoka; Tetsuo Nakajo (pp. 47-52).
Metal fluorides are more stable than metals and metal oxides; therefore, no oxides can be applied as catalyst supports for the reactions in which hydrogen fluoride is involved. The authors observed that metal phosphates are not reactive to HF at higher reaction temperatures such as 973K. Hence, the decomposition of CClF2CClF2 was studied over Pt-supported SiO2, Al2O3, and AlPO4-based catalysts. Hydrodehalogenation proceeded and CHF2CClF2 and C2H6 were formed as major products, small amounts of CHF2CHF2, CH2FCClF2, CH2FCF3, and CH4 were also formed. Pt/SiO2 was the most active; however, SiO2 reacted with HF and the SiF4 formed sublimated. Following these, Al2O3 was the most active; however, it reacted with HF to form AlF3 and was deactivated. Similar hydrodehalogenation proceeded over Pt/AlPO4 and Pt/(CePO4AlPO4). The crystal structure of these catalysts did not change during the catalytic reaction, although the reduction of specific surface areas (SSA) was observed. Therefore, AlPO4 and Ce containing AlPO4 are suitable as catalyst supports in reactions in which HF is involved. XPS showed that the electronic effects of AlPO4 lie between that of SiO2 and Al2O3. A good linear relationship is found to exist between the initial reaction rates per unit surface area of Pt metal supported on the supports and the binding energy of supported Pt. This suggests that the more cationic the Pt, the more easily it could abstract Cl− from CClF2CClF2.
Keywords: AlPO; 4; Catalyst support; Hydrogen fluoride; CFCs; Halogenated hydrocarbons
Effect of SO2 and H2S on CO preferential oxidation in H2-rich gas over Ru/Al2O3 and Pt/Al2O3 catalysts by Hidenobu Wakita; Yukimune Kani; Kunihiro Ukai; Takeshi Tomizawa; Tatsuya Takeguchi; Wataru Ueda (pp. 53-61).
The influence of the addition of 2.1 or 21ppm SO2 or 2.1, 4.3 or 48ppm H2S to reaction gas composed of 51.5vol.% H2, 0.3vol.% CO, 13.0vol.% CO2, 0.5vol.% O2, 6.0vol.% N2, and 28.8vol.% H2O on the activity for the CO preferential oxidation was investigated. The catalysts used for the reaction tests were monolith Ru/Al2O3 and Pt/Al2O3 catalysts with Ru loading of 1.6g/l and Pt loading of 3.1g/l, respectively. Pellet 3.8wt.% Ru/Al2O3 and 3.8wt.% Pt/Al2O3 catalysts were also used to elucidate the deactivation mechanisms. The addition of a high concentration of SO2 or H2S decreased the activity for the CO preferential oxidation. The XPS and IR spectrum for the SO2-poisoned Ru/Al2O3 catalyst showed that Ru particles adsorbed SO42− species, while the XPS for both SO2- and H2S-poisoned Pt/Al2O3 catalysts showed that Pt particles adsorbed S2− species. The activities of the Ru/Al2O3 catalyst for both CO and H2 oxidations were lowered in the presence of the sulfur compounds; the selectivity of CO oxidation was almost constant during the poisoning reaction. On the other hand, the activity of the Pt/Al2O3 catalyst for CO oxidation was lowered by small amounts of the sulfur compounds, while the activity for H2 oxidation was almost constant; the selectivity of CO oxidation decreased. The poisoned Pt catalysts were regenerated by the calcination at 175°C, and the covering S2− species was oxidized to SO42− species, which migrated to the Al2O3 support.
Keywords: CO preferential oxidation; SO; 2; H; 2; S; Ru/Al; 2; O; 3; catalyst; Pt/Al; 2; O; 3; catalyst
Standardization of catalyst preparation using reference catalyst: ion exchange of mordenite type zeolite by Naonobu Katada; Tatsuya Takeguchi; Tatsuya Suzuki; Toshihisa Fukushima; Kinya Inagaki; Setsuo Tokunaga; Hiromichi Shimada; Koichi Sato; Yasunori Oumi; Tsuneji Sano; Kohichi Segawa; Kazuyuki Nakai; Hiroshi Shoji; Peng Wu; Takashi Tatsumi; Takayuki Komatsu; Takao Masuda; Kazunari Domen; Eisuke Yoda; Junko N. Kondo; Toshio Okuhara; Yasuyoshi Kageyama; Miki Niwa; Masaru Ogura; Masahiko Matsukata; Eiichi Kikuchi; Noriyasu Okazaki; Motoi Takahashi; Akio Tada; Shogo Tawada; Yoshihiro Kubota; Yoshihiro Sugi; Yasuhiko Higashio; Masahiko Kamada; Yukiyo Kioka; Kohei Yamamoto; Takayuki Shouji; Yusaku Arima; Yasuaki Okamoto; Hideyuki Matsumoto (pp. 63-74).
A joint study was organized to establish a standard set of conditions for the ion exchange of zeolite from sodium into proton-form. The sodium-form mordenite with Si/Al2=ca. 15 was ion exchanged into an NH4-form, followed by calcination according to various recipes. Then various advanced techniques for characterization (ICP, TG, XPS, SEM, XRD, N2 adsorption,29Si and27Al NMR, benzene diffusion, IR of OH and adsorbed pyridine and CO, ammonia TPD) were applied, and some test reactions (cracking of cumene, isopropylation of biphenyl, oligomerization of propene and chichibabin condensation of acetaldehyde and ammonia into picoline) were conducted. The ion exchange (removal of sodium) proceeded as expected, but remarkable differences were observed in physicochemical and catalytic properties of the thus-prepared proton-form samples. Exceptionally high temperature (383K) for the ion exchange resulted in the structural degradation, while most samples exchanged at 333–353K maintained the crystallinity and pore volume. The use of NH4Cl slightly changed the crystal morphology. Extra-framework aluminum species was formed on most samples after calcination above 773K. In contrast, calcination at 673K maintained the framework aluminum. Therefore, the dealumination is considered to proceed after complete removal of ammonia from the ammonium-form zeolite. However, the proton-form zeolite was stable under dry conditions, so it is speculated that the dealumination was induced by the contact of the proton-form zeolite to atmosphere with humidity. The total and Brønsted acidity decreased with the dealumination, while Lewis acidity increased. On the other hand, rapid heating of the ammonium type zeolite caused narrowing of the micropores. These structural changes seriously affected the catalytic activities for various reactions.
Keywords: Catalyst preparation; Standardization; Ion exchange; Mordenite; Zeolite; Reference catalyst; Dealumination; Acidity
Standardization of catalyst preparation using reference catalyst: ion exchange of mordenite type zeolite by Naonobu Katada; Tatsuya Takeguchi; Tatsuya Suzuki; Toshihisa Fukushima; Kinya Inagaki; Setsuo Tokunaga; Hiromichi Shimada; Koichi Sato; Yasunori Oumi; Tsuneji Sano; Kohichi Segawa; Kazuyuki Nakai; Hiroshi Shoji; Peng Wu; Takashi Tatsumi; Takayuki Komatsu; Takao Masuda; Kazunari Domen; Eisuke Yoda; Junko N. Kondo; Toshio Okuhara; Takahide Kanai; Miki Niwa; Masaru Ogura; Masahiko Matsukata; Eiichi Kikuchi; Noriyasu Okazaki; Motoi Takahashi; Akio Tada; Shogo Tawada; Yoshihiro Kubota; Yoshihiro Sugi; Yasuhiko Higashio; Masahiko Kamada; Yukiyo Kioka; Kohei Yamamoto; Takayuki Shouji; Shigeo Satokawa; Yusaku Arima; Yasuaki Okamoto; Hideyuki Matsumoto (pp. 75-84).
The undesired structural change of mordenite with Si/Al2=15 during the ion exchange and during calcination from the sodium form into proton form, especially the dealumination after the calcination, was studied. The29Si NMR results clarified that calcination of the NH4-form mordenite with Si/Al2=15 at >ca. 800K, followed by the contact of proton-form sample with the atmosphere containing humidity, induced the dealumination. However, the samples carefully kept free from humidity after the heat treatment showed no dealumination or only a low degree of it. The27Al NMR and ammonia TPD results agreed with these findings. The origin of dealumination is thus considered to be the contact of the proton-form sample with humidity after the calcination. On the other hand, the dealumination was not observed after calcination at <673K. The1H NMR indicated that the ca. 1/3 of the ion-exchange sites were blocked by the ammonium cations after calcination at 673K, suggesting that the dealumination was prevented by the ammonium cations. On the basis of these findings, a standard set of conditions in which one can safely prepare the proton-form zeolite with high quality is proposed. The recommended temperature for the ion exchange is room temperature, because it is high enough to exchange the ions in this case. The most important variable is the calcination temperature; it should be lower than 673K in order to avoid the dealumination. These conditions were confirmed to yield zeolites with a high framework aluminum content and ordinary catalytic performance.
Keywords: Catalyst preparation; Standardization; Ion exchange; Mordenite; Zeolite; Reference catalyst; Dealumination; Acidity
New and efficient heterogeneous catalytic system for Heck reaction: palladium colloid layer in situ reduced in the channel of mesoporous silica materials by Liang Li; Ling-Xia Zhang; Jian-Lin Shi; Ji-Na Yan; Jian Liang (pp. 85-89).
The synthesis and characterization of palladium colloid layer grafted mesoporous SBA-15 material, designated as Pd-SBA, are described. In the preparation of this new catalyst, the SiH functional groups were introduced into the channel of SBA-15 mesoporous materials resulting in highly dispersed metal colloid layer on the pore walls of the supporting material. The material is investigated for Heck coupling reactions with activated and non-activated aryl substrates. The ultrahigh specific area, large pore opening, and highly dispersed catalyst species in Pd-SBA material create one of the most active heterogeneous catalysts for Heck coupling reactions.
Keywords: Heck reaction; Palladium; Heterogeneous catalysis; Zeolites
The role of vanadium on the properties of iron based catalysts for the water gas shift reaction by Ivan Lima Júnior; Jean-Marc M. Millet; Mimoun Aouine; Maria do Carmo Rangel (pp. 91-98).
The substitution of chromium by vanadium as dopant in the iron oxide based water gas shift (WGS) catalyst has been investigated. Catalysts prepared as magnetite with different amount of vanadium have been prepared and tested with different amounts of water in the gas feed. The results obtained showed that vanadium was a promising dopant leading to very active and stable catalysts. The vanadium-doped catalysts have been characterized by means of chemical analysis, X-ray diffraction, Fourier transform infrared spectroscopy, specific surface area measurements, temperature-programmed reduction, Mössbauer spectroscopy, X-ray photoelectron spectroscopy and high resolution transmission electron microscopy with electron diffraction. Vanadium has been shown to be present both as V(III) and V(IV) species at the surface and in the bulk near the surface of the magnetite structure. It increased the specific surface area of the catalysts and kept the particles apart on the surface delaying sintering. The vanadium doping has been shown to have also an effect on the Fe(III) content of the magnetite which increased favoring the successive oxidation and reduction cycles, during the reaction.
Keywords: Magnetite; Hydrogen; WGSR; Vanadium; Iron oxide
Kinetics of the homogeneous hydrogenation of avermectins catalyzed by RhCl(Ph3P)3 complexes by Patricia D. Zgolicz; María I. Cabrera; Ricardo J. Grau (pp. 99-109).
The kinetics of the hydrogenation of avermectins B1a and B1b catalyzed by RhCl(Ph3P)3 complexes was studied in a temperature range of 298–328K at 275.7kNm−2, using catalyst loading in the range of 0.75–7.25wt.% with respect to the avermectins in toluene solution. The effects on the hydrogenation rate of the catalyst, avermectins, and hydrogen concentrations were determined under complete induction time suppression and without catalyst deactivation. Rate equations were developed for various kinetic schemes on the basis of the main steps suggested by Wilkinson for simple olefin hydrogenation and fitted to the experimental data. A statistical analysis of regression using three plausible mechanisms of reaction allows a discussion on the adequacy of the models to approach the observed half-order reaction with respect to the catalyst loading and first-order to avermectins and hydrogen concentrations. A reaction mechanism featuring non-extensive simple dissociation of the catalyst precursor and reaction pathway along the hydride route with the rate-determining olefin coordination step proved fair enough to describe the hydrogenation of this macrocyclic lactone. The physical reasonability of the equilibrium and kinetic parameters was also discussed.
Keywords: Avermectins; Hydrogenation; Wilkinson catalyst; Rhodium complexes; Kinetic modeling
Selective transesterification of triolein with methanol to methyl oleate and glycerol using alumina loaded with alkali metal salt as a solid-base catalyst by Takahiro Ebiura; Tsuneo Echizen; Akio Ishikawa; Kazuhito Murai; Toshihide Baba (pp. 111-116).
Selective transesterification of triolein (trioleoyl glycerol) with methanol to methyl oleate and glycerol could be achieved at around 333K using alumina loaded with alkali metal salt as a solid-base catalyst. The catalytic activities are shown to be relatively insensitive to the presence of water. A K2CO3-loaded alumina catalyst prepared by evacuation at 823K gives methyl oleate and glycerol in the highest yields of 94 and 89%, respectively, at 333K in 1h.This catalyst also effectively catalyzes the glycerolysis of triolein with glycerol to give dioleoyl glycerol in 71% yield at 453K in 5h.
Keywords: Transesterification; Triolein; Glycerol; Methanol; Biodiesel
Selective epoxidation of allyl acetate with tert-butyl hydroperoxide over MoO3/MgO by Kenta Shimura; Hiroyoshi Kanai; Kazunori Utani; Kazuo Matsuyama; Seiichiro Imamura (pp. 117-124).
Highly selective epoxidation of allyl acetate was carried out over MoO3/MgO using tert-butyl hydroperoxide as an oxidizing agent. The catalytically active species was identified as monolayer MgMoO4 on MgO. MgO with large pores is suitable for selective epoxide formation. The highest yield of glycidyl acetate was obtained over 7wt.% MoO3/MgO, in which MgMoO4 species were highly dispersed on the surface of MgO. Trialkyl borates were good promoters for selective epoxide formation. Among them, triisopropyl borate afforded the highest yield of 92%.1H and11B NMR measurements of a homogeneous MoO2(acac)2-B(OBu n)3-( t-C4H9OOH) system showed that alkyl groups of the borate exchange with t-butyl hydroperoxyl group, and that the boron atom interacts with the oxygen of MoO, promoting reactivity of an oxygen atom in the hydroperoxyl group to attack the double bond of allyl acetate.
Keywords: Epoxidation; Allyl acetate; tert; -Butyl hydroperoxide; MoO; 3; /MgO; DR–UV–vis; XANES; Trialkyl borate
Hydrogen production by oxidative methanol reforming on Pd/ZnO by Shetian Liu; Katsumi Takahashi; Kazuo Uematsu; Muneo Ayabe (pp. 125-135).
Pd/ZnO catalysts with Pd loadings of between 1 and 45% were prepared by impregnation and coprecipitation methods; their catalytic performances during oxidative methanol reforming for the production of hydrogen were investigated under various reaction conditions. The prepared catalysts showed high activity and selectivity towards hydrogen formation. At higher Pd loading (exceeding 5%), the coprecipitation method was superior to the impregnation method for the preparation of the catalyst. Highly active Pd/ZnO that is comparable to commercial Cu–Zn catalyst can be obtained with high Pd loadings. On the other hand, CO formation was greatly reduced by increasing the Pd loading. Excess amounts of Pd on the ZnO decreased the conversion of methanol and increased CO formation. XRD characterization of freshly prepared and spent catalysts confirmed the formation of the Pd–Zn alloy. The sizes of both the ZnO and the Pd–Zn crystallites affect the catalytic performance. A strong interaction between the Pd–Zn alloy and the ZnO support is believed to be essential for the selective formation of hydrogen. The reaction mechanism and the CO formation route are also discussed, based on the results that we obtained.
Keywords: Hydrogen production; Oxidative steam reforming; Methanol; Palladium; Palladium–zinc alloy; Zinc oxide
Catalytic growth of carbon fibers from methane and ethylene on carbon-supported Ni catalysts by Katsuomi Takehira; Takenori Ohi; Tetsuya Shishido; Tomonori Kawabata; Ken Takaki (pp. 137-145).
Catalytic decompositions of methane and ethylene to carbon nanofibers (CNFs) and hydrogen have been carried out on various carbon-supported Ni catalysts at 823K. Graphite (GP), active carbon (AC), and CNFs were used as the carbon supports. The CNFs used as the catalyst supports were prepared by the catalytic decomposition of methane over Ni/SiO2 catalysts at 823K, followed by removing the catalyst with hydrofluoric acid and nitric acid. All carbon materials were treated by nitric acid and/or hydrogen peroxide, and were used as the supports for impregnation in aqueous solution of Ni(II) nitrate to form Ni/carbon catalysts. After the pre-treatments, the sizes of Ni metal particles formed on the carbon supports were smaller compared with those formed on non-treated carbon supports except for AC. AC was already activated by pre-treatment as purchased and was therefore not affected by the treatment. An impregnation of non-treated GP and CNFs in acetone solution of Ni(II) nitrate also afforded small-sized Ni metal particles, indicating the important role of interactions between carbon surface and Ni(II) nitrate solution during the impregnation. These suggest that the surface of GP and CNFs, which was originally hydrophobic, changed to hydrophilic after the pre-treatments, resulting in the formation of well-dispersed Ni metal particles due to strong interaction between the carbon surface and aqueous solution of Ni(II) nitrate. When methane and ethylene were decomposed over the Ni/carbon catalysts, smaller-sized Ni metal particles produced larger amounts of CNFs; moreover, ethylene formed larger amounts of CNFs than methane. It was confirmed on Ni/CNF catalysts that smaller-sized sec-CNFs grew on the well-dispersed Ni metal particles strongly bound to the surface of treated CNFs, while larger-sized sec-CNFs grew with Ni metal particles anchored on the tip or encapsulated inside the CNFs on non-treated CNFs. By removing Ni metal particles from the samples after the decomposition with nitric acid, cross-linked or multi-layered carbon materials between the original carbon and the secondarily formed CNFs were obtained.
Keywords: Carbon-supported Ni catalyst; Catalytic decomposition; Methane; Ethylene; Cross-linked carbon nanofibers
Study on single-stage hydrocracking of vacuum residue in the suspension of Ni–Mo catalyst by Jan Mosio-Mosiewski; Ireneusz Morawski (pp. 147-155).
Activity of the Ni–Mo/Al2O3 catalyst was studied in a single-stage hydrocracking process of vacuum residue (VR) of Ural crude. The process was carried out in a continuous flow reactor, at the temperature of 410–450°C, at the pressure of 12–20MPa, at the liquid space velocity of 0.25–0.75h−1 and at the gas space velocity of 2500h−1, and a suspension of the catalyst tested was used. The catalyst was found efficient for the hydrogenation processes, inclusive of hydrodesulphurisation processes, but its cracking activity was moderate. The catalyst concentration and hydrogen pressure did not affect significantly the VR hydrocracking process over the studied scope of parameters, and only some small effect was noticed on hydrodesulphurisation of the cracking products. On the other hand, the reaction temperature and LHSV were found to strongly affect the VR hydrocracking process and to reduce the contents of asphaltenes and CCR, while the impact on hydrodesulphurisation was lower. The reaction rates and activation energy values were determined for those reactions. The conversion figure for VR to distillates (bp<538°C) reached 61.6–88.7wt.% at 430°C, and sulphur was converted at 70–85wt.%.
Keywords: Vacuum residue; Hydrocracking; Hydrodesulphurisation; Ni–Mo catalyst; Asphaltenes
Hydroconversion of cyclohexene using catalysts containing Pt, Pd, Ir and Re supported on H-ZSM-5 zeolite by Ahmed K. Aboul-Gheit; Sameh M. Aboul-Fotouh; Noha A.K. Aboul-Gheit (pp. 157-164).
The hydroconversion of cyclohexene (CHE) using catalysts containing 0.35wt.% of either Pt, Pd, Ir or Re on H-ZSM-5 support as well as the unloaded H-ZSM-5 zeolite was carried out using a flow-type fixed-bed reactor in a continuous flow of H2 gas. The hydroconversion of CHE was found to include its hydrogenation to CHA, dehydrogenation to benzene through cyclohexadienes (CHDEs) as intermediates, its isomerisation to the C5 ring containing cycloolefins (methylcyclopentenes, MCPEs) followed by their hydrogenation to methylcyclopentane (MCPA). Moreover, hydrocracking and alkylation products (toluene and xylenes) were found to form at higher temperatures. Hydrogenation and dehydrogenation reactions not only took place on the metal sites, but also on the unloaded zeolite at comparatively higher temperatures. The hydrogenation/dehydrogenation activities of the current metals were found to be in the order: Pd>Pt>Ir>Re. However, rhenium was almost catalytically inactive on all hydroconversion steps.
Keywords: Pt; Pd; Ir; Re; H-ZSM-5 zeolite; Cyclohexene; Hydroconversion; Hydrogenation; Dehydrogenation; Isomerisation; Hydrocracking; Alkylation
Factors influencing selectivity in naphthalene hydrogenation over Au- and Pt–Au-supported catalysts by B. Pawelec; A.M. Venezia; V. La Parola; S. Thomas; J.L.G. Fierro (pp. 165-175).
The effects of the support (γ-Al2O3 and SiO2) and of the preparation method (the reduction of metal precursors by ethanol in the presence of polyvinylpyrrolidone (PVP) versus impregnation (IMP)) on the activity and selectivity of the Au and Pt–Au catalysts in naphthalene hydrogenation ( P=2.0MPa, T=448K, WHSV=45.7h−1) were studied. The physico-chemical characteristics of the catalysts were evaluated by X-ray diffraction, N2 adsorption–desorption isotherms, DRIFT spectroscopy of the adsorbed CO, thermogravimetric (TG) and X-ray photoelectron spectroscopy techniques. Activity data for the target reaction showed that the SiO2-supported catalysts are slightly better than the γ-Al2O3-supported counterparts. The monometallic Au/Al catalyst prepared by the IMP method displayed comparable selectivity but larger activity (mmols−1molesAu(Pt)−1) than its homologue prepared by the PVP method. As derived from X-ray line broadening analysis, this is due to much better dispersion of gold particles when using the IMP method. For SiO2-supported catalysts prepared by PVP method, the initial activity followed the trend: 1Au>1Pt–1Au>2Pt. Both the monometallic Au/Si and 2Pt/Si exhibited quick deactivation contrary to the binary 1Pt–1Au/Si-pvp sample exhibiting higher activity at long time on stream. In this sample a synergy effect between Pt and Au was attributed to Pt50Au50 alloy formation. The factors controlling the selectivity in naphthalene hydrogenation on gold catalysts are discussed.
Keywords: Naphthalene hydrogenation; Silica; Alumina; Au–Pt catalysts
Catalytic activity of Cu-based amorphous alloy ribbons modified by cathodic hydrogen charging by M. Pisarek; M. Janik-Czachor; Á. Molnár; K. Hughes (pp. 177-184).
Since hydrogen is known to be one of the most efficient embrittling atomic species, cathodic hydrogen charging was used in an attempt to modify the structure, composition, and morphology of Cu-based amorphous alloy ribbons. Various methods of analysis such as X-ray electron microanalysis, SEM, high resolution Auger microanalysis (SAM), with varying lateral resolution and different information depths, as well as measurements of specific surface area, porosity and catalytic tests, were used to follow the changes within the ribbons and at the surface, and their interrelations with catalytic activity. The activity in a test reaction (dehydrogenation of 2-propanol) was enhanced up to conversion levels of 66% for Cu–Ti and of 88% for Cu–Hf, which are much higher than those obtained with all other pre-treatments previously applied. The rather low specific surface area and porosity, as well as a lack of Cu0 both before and after the catalytic test suggest that the generally accepted mechanism for the dehydrogenation of alcohols over copper catalysts with the involvement of Cu0 is not operative here.
Keywords: Cu-based amorphous alloys; Devitrification; Cu segregation; Hydrogen charging; Catalytic dehydrogenation; SEM; Auger microanalysis (AES; SAM)
Rhodium(I) and rhodium(III)–heteropolyacids supported on MCM-41 for the catalytic hydroformylation of styrene derivatives by B. El Ali; J. Tijani; M. Fettouhi; M. El-Faer; A. Al-Arfaj (pp. 185-196).
Rh supported catalysts were prepared by impregnating rhodium(I) and rhodium(III) complexes with and without heteropolyacids for the hydroformylation of styrene derivatives. The effect of the pore size of MCM-41 was considered. The addition of water showed a promoting effect with Rh(III) based catalysts. The amount of water showed also a big effect on the catalytic activity of the Rh(III) supported catalyst. The change of the temperature affects the selectivity of the reaction time of the reaction. Different heteropolyacids such as H3PMo12O40· xH2O (HPA-Mo12) and H3PW12O40· yH2O (HPA-W12) were used as co-catalysts that were impregnated along with rhodium complexes on the inorganic supports. The results showed a clear effect of the heteropolyacid H3PW12O40· yH2O (HPA-W12) in increasing the catalytic activity of the rhodium supported catalyst.
Keywords: Hydroformylation; MCM-41; Zeolites; Clay; Rhodium; Heteropolyacid; Styrene; Phosphine ligands; Syngas
Role of acidity and microporous structure in alternative catalysts for the transformation of methanol into olefins by Andrés T. Aguayo; Ana G. Gayubo; Raquel Vivanco; Martin Olazar; Javier Bilbao (pp. 197-207).
The transformation of methanol into light olefins (C2–C4) has been studied on several acid catalysts prepared by agglomerating different microporous acid phases (SAPO-11, SAPO-18, SAPO-34 and beta-zeolites) with bentonite and inert alumina. SAPO-11s and beta-zeolites have been prepared under different conditions and, consequently, they have different porous structure, total acidity and site acid strength. An analysis is made of the influence of their properties (micropore diameter, total acidity, acid strength and site density on their surface) on the kinetic behaviour of the catalysts (initial conversion and selectivity to olefins and deactivation rate). The catalyst SAPO-18 has a lower deactivation rate than the SAPO-34 due to a slightly lower acid strength and to a lower density of strong acid sites on the surface. This behaviour and the lower preparation cost make SAPO-18 an interesting alternative to SAPO-34, which is the one used in industry in the MTO process.
Keywords: MTO process; Microporous catalysts; Surface acidity; Catalyst deactivation
Oxidation of isobutane over complex oxides containing V, Nb, Ta, and Mo under aerobic and anaerobic reaction conditions by Yusaku Takita; Kayo Kikutani; Ching Xia; Hideaki Takami; Katsutoshi Nagaoka (pp. 209-216).
Isobutane oxidation over single metal oxides of V, Nb, Ta, and Mo and over their complex oxides was studied. The most active was V2O5, while medium activity was shown by LaVO4, BiVO4, CaV2O6, Ta2O5, TaV2O6, ZnNb2O6, Nb2O5, MgV2O6, YVO4, Cu2V2O7, MoO3 and MnNb2O5. The less active oxides were Na2MoO4 and Ag2MoO4. Isobutane was oxidized mainly to isobutene and CO x, but isobutene selectivity was generally lower than 50% below 673K. Relatively high isobutene selectivity was shown by MgTa2O6, TaV2O6, and ZnNb2O6. Methacroleine was only obtained over MoO3 and methanol was formed only over V2O5 and Cu2V2O7. Acetic acid was formed over certain V-containing oxides. No oxygen-containing products were formed over Nb- and Ta-containing oxides. On a unit surface area basis, Nb2O5 and Ta2O5 have higher oxidizing activity than V2O5 and MoO3.Isobutane oxidation was studied in the absence of gaseous O2 over MV2-type complex oxides. Catalytic activity was determined as follows:CuV2O6≫CoV2O6>MgV2O6>ZnV2O6≫ZrV2O7>CaV2O6. MgV2O6 is the most selective for isobutene formation. Combination to easily redoxable metal ions tends to accelerate the deep oxidation process. There may be a threshold for the initial reaction rate of lattice oxygen per unit surface area for selective isobutene formation. Selective isobutene formation continued until a reduction of MgV2O6 by at least 4.5%, had finished and the reduced catalyst was recovered by the calcination at 773K. Selective formation of isobutene made it possible to combine oxidations of isobutane with MgV2O6 and with the oxidations of reduced catalysts.
Keywords: Anaerobic oxidation; Isobutane; Vanadium oxide; Niobium oxide; Tantalum oxide
The preparation and catalytic behavior of copper–cerium oxide catalysts for low-temperature carbon monoxide oxidation by Xiu-Cheng Zheng; Shi-Hua Wu; Shu-Ping Wang; Shu-Rong Wang; Shou-Min Zhang; Wei-Ping Huang (pp. 217-223).
CeO2 nano-crystals were synthesized by a sol–gel process and then used as support for CuO/CeO2 (sol–gel) catalysts prepared via impregnation method. For comparison, the commercial CeO2 was also used as a support for CuO/CeO2 (commercial) catalysts prepared via the same method. The samples were characterized by means of BET, XRD, UV–vis, TPR and XPS. The catalytic properties of the CuO/CeO2 catalysts for low-temperature CO oxidation were studied by using a microreactor-GC system. The prepared spherical CeO2 nano-crystals have much smaller particle size, better crystallinity and larger surface area than the commercial CeO2. XPS analysis indicated the presence of reduced copper species in the CuO/CeO2 catalysts. TPR showed that there are different copper species in the catalysts. The influence of calcination time, temperature and CuO loadings on the catalytic activity of CuO/CeO2 catalysts has been studied. The CuO/CeO2 (sol–gel) catalysts exhibited higher catalytic activity than the CuO/CeO2 (commercial) catalysts. Compared with CuO/CeO2 catalysts prepared via other techniques, our catalysts exhibited similar or even better catalytic performance.
Keywords: Sol–gel method; CeO; 2; CuO/CeO; 2; Carbon monoxide oxidation
Methane combustion over Pd/SiO2 catalysts with different degrees of hydrophobicity by P. Araya; S. Guerrero; J. Robertson; F.J. Gracia (pp. 225-233).
The combustion of methane has been studied over 1% Pd catalysts supported on commercial silica with different hydrophobicity, prepared by chlorine free precursors. It was found that, when no water is added to the feed, the degree of hydrophobicity of the silica does not affect significantly the behavior of the catalysts. The results show that the activation and deactivation processes are similar for both catalysts. Furthermore, contrary to what is observed on Pd/Al2O3 and Pd/ZrO2 catalysts, the apparent reaction order with respect to water for Pd/SiO2 catalysts is −0.25. When water is added to the feed, however, the different hydrophobicity of the supports affects the inhibition produced by the adsorption of water on the catalytic surface. Regardless of the hydrophobicity of the support, the addition of water also speeds up the deactivation process of the Pd catalysts supported on silica.
Keywords: Methane combustion; Supported Pd catalyst; Silica; Zirconia; Water inhibition
Hydrogen storage by decalin/naphthalene pair and hydrogen supply to fuel cells by use of superheated liquid-film-type catalysis by Shinya Hodoshima; Shigeki Takaiwa; Atsushi Shono; Kazumi Satoh; Yasukazu Saito (pp. 235-242).
A catalytic reaction pair of decalin dehydrogenation/naphthalene hydrogenation has been proposed as a storage medium for fuel-cell hydrogen in mobile modes. The hydrogen capacities with decalin (7.3wt.%, 64.8kg-H2m3) are higher than the target values of the Department of Energy, USA (6.5wt.%, 62.0kg-H2m3).Platinum–rhenium composite catalysts supported on granular activated carbon in “superheated liquid-film� states gave excellent reactivities for decalin dehydrogenation, where the conversion of almost 100% from decalin to naphthalene was attained within 1h by heating at 280°C in a batch-wise reactor. “Superheated liquid-film� conditions were also realized in a continuous-type reactor at the same temperature (280°C). With the goal of maintaining rapid evolution of hydrogen stationarily, a rather wide range of decalin feed rates was allowable with use of platinum particles supported on activated carbon cloth. Decalin should be evaluated as an organic chemical hydride not only because of its storage densities but also because of its potential power densities for fuel-cell vehicles.
Keywords: Decalin dehydrogenation/naphthalene hydrogenation pair; Reactive distillation conditions; Superheated liquid-film-type catalysis; Carbon-supported platinum-based catalysts; Continuous operation
Oxycracking of hydrocarbons: chemistry, technology and economic potential by J.-P. Lange; R.J. Schoonebeek; P.D.L. Mercera; F.W. van Breukelen (pp. 243-253).
In 1993, Huff and Schmidt reported the oxydehydrogenation of ethane to ethene at millisecond contact time. Shell Chemicals performed a study to confirm these claims and explore the technical scope and economic potential of this technology. The technical and economical results are summarised here and compared with various oxydehydrogenation and oxycracking studies that have been reported in the literature since then. Beyond confirming the initial claims and later findings, we also disclose new results such as the conversion of methane to ethene and the cracking alkenes to alkynes and dienes. The economic analysis concluded that this technology would at best provide marginal cost benefits over the existing steam cracker technology. However, it does not offer sufficient economic advantages to justify the development costs and take the implementation risks. The same seems to apply to several oxycracking technologies reported in the literature.
Keywords: Alkanes; Alkenes; Alkynes; Dienes; Cracking (oxidative or oxy-); Cracking (steam); Oxidation (partial); Dehydrogenation (oxidative); Platinum; Economics
Palladium-based alloy and monometallic catalysts for gas phase hydrogenation of crotonaldehyde: effects of alloying and alloy crystallite size by Nobuhiro Iwasa; Masanori Takizawa; Masahiko Arai (pp. 255-263).
Gas phase hydrogenation of crotonaldehyde has been investigated with supported Pd catalysts using different supports. The overall conversion and product distribution significantly depend on the supports used. Crotyl alcohol is formed along with butyraldehyde as the chief products in comparable quantities with Pd/ZnO, while little crotyl alcohol is formed with such catalysts as Pd/Al2O3 and Pd/SiO2. The difference in the product distribution is due to the difference in the active species, which is PdZn alloy in Pd/ZnO but is Pd in the other catalysts. The activity of Pd/ZnO decreases slightly with the size of PdZn alloy crystallites, but the selectivity to crotyl alcohol increases and that to butyraldehyde decreases.
Keywords: Crotonaldehyde; Hydrogenation; Pd–Zn alloy; Crotyl alcohol