Applied Catalysis A, General (v.288, #1-2)
Cobalt oxide/γ-alumina catalysts prepared by equilibrium deposition filtration: The influence of the initial cobalt concentration on the structure of the oxide phase and the activity for complete benzene oxidation by Theodora Ataloglou; Christina Fountzoula; Kyriakos Bourikas; John Vakros; Alexis Lycourghiotis; Christos Kordulis (1-9).
In the present work we studied the influence of the initial concentration of the impregnating solution used for mounting Co(II) species on the γ-alumina surface by equilibrium deposition filtration method (edf) on the physicochemical properties and the catalytic activity of the “cobalt oxide”/γ-alumina catalysts. The complete oxidation of benzene has been used as a model reaction.Two series of catalysts (edf-X-A and edf-X-B) of varying Co content (X: up to 21 wt.% Co) were prepared using the above-mentioned method and tested at various temperatures in the range 200–300 °C using a fixed-bed reactor. In the first series (A) various Co loadings were obtained by varying the initial Co(II) concentration of the impregnating solution. In the second series (B) the corresponding Co loadings were obtained by using the impregnating solution used for the preparation of the catalyst of A series with the maximum Co(II) content and varying the impregnation time. All catalysts were characterized using various techniques, X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), X-ray powder analysis (XRD), nitrogen adsorption (BET) and temperature-programmed reduction (TPR).It was found that the initial Co(II) concentration of the impregnating solution used for depositing the corresponding species on the γ-alumina surface by edf influences the catalytic activity of the “cobalt oxide”/γ-alumina catalysts with respect to the complete oxidation of benzene. The increase of the initial Co(II) concentration of the impregnating solution brings about a change in the composition of the deposited phase formed in the impregnation step by decreasing the ratio “Co(II) surface inner-sphere complexes/surface Co(II) precipitates”. Upon calcination, the Co(II) surface inner-sphere complexes are transformed to well-dispersed “cobalt oxide” phase strongly interacting with the support surface while the surface Co(II) precipitates are transformed to Co3O4 crystallites loosely interacting with the support surface. The former phase is responsible for the relatively high dispersion of Co observed in the A series of catalysts but it is rather inactive, while the latter exhibits lower dispersion but higher activity. Thus, the edf catalysts prepared using high initial Co(II) concentration exhibited higher catalytic activity than the corresponding ones prepared using low initial Co(II) concentration.
Keywords: Cobalt oxide catalysts; Preparation method; Equilibrium adsorption; VOCs combustion; Benzene oxidation; DRS; XPS; TPR;
TiO2-supported iron–molybdenum hydrodesulfurization catalysts by A. Spojakina; E. Kraleva; K. Jiratova; L. Petrov (10-17).
TiO2-supported Mo (6 and 12 wt.%) and Fe (0.25–1.0 wt.%) containing catalysts have been prepared using H3PMo12O40 heteropolyacid (HPMo) and Fe salt of HPMo. Catalysts have been characterized by BET, SEM, IR, TPR, XPS methods and by their HDS activity in the reaction of thiophene conversion. Promoting effect of TiO2 on Mo catalysts was confirmed, higher in case of catalysts with low Mo concentration (6 wt.%) than in case of the catalyst with 12 wt.% Mo. The highest HDS activity and stability was observed after introducing Fe in the form of HPMo countercation (Fe/Mo ∼ 0.1). Iron increases concentration of Mo6+ and Mo5+ in octahedral coordination. After sulfidation, the Fe-containing catalysts show presence of different Mo valence states (Mo4+, Mo5+, Mo6+), Fe―P, Mo―P and/or Fe―Mo―P bonds that affect the HDS catalytic activity.
Keywords: Heteropolycompounds; Titania support; Iron promotor; Thiophene conversion; IR; TPR; XPS;
Repeated use of supported H3PW12O40 catalysts in the liquid phase esterification of acetic acid with butanol by J.H. Sepúlveda; J.C. Yori; C.R. Vera (18-24).
Tungstophosphoric acid (HPA) catalysts supported over SiO2, ZrO2 and carbon were prepared and characterized. Its repeated use in the liquid phase reaction of esterification of acetic acid with butanol was particularly studied. The results revealed that silica- and zirconia-supported HPA had an intrinsic activity per unit protonic acid site greater than that of an Amberlyst W35 resin. Its repeated use was, however, impeded because of the dissolution of HPA in the reaction medium. Carbon-supported HPA catalysts had a slightly lower activity but they displayed a sustained conversion level upon reuse in subsequent catalytic tests. Inspection of the solvent media after the reaction in a UV–visible spectrophotometer revealed that both butanol and water leached HPA from the silica- and zirconia-supported catalysts and that the effect was minimal in the case of the carbon catalysts. It was rationalized that [PW12O40]3− anions are strongly adsorbed at pH 1–2 on the carbon support due to the electrostatic interaction with the carbon surface protons of zero-point-of-charge (ZPC) equal to 6.
Keywords: Supported heteropolyacids; Esterification; Reuse;
Catalytic application of Al-MCM-41 in the esterification of acetic acid with various alcohols by B. Rabindran Jermy; A. Pandurangan (25-33).
Mesoporous Al-MCM-41 molecular sieves in four Si/Al ratios: 25, 50, 75 and 100, were synthesised under hydrothermal condition. They were characterized using powder X-ray diffraction (XRD), FT-IR, BET and thermogravimetric–differential thermal analysis (TGA–DTA). The XRD spectra showed that the materials were of hexagonal mesoporous structure. The FT-IR spectra revealed the order of the hydrophobic character of the catalyst materials when one compared the broad envelopes due to the O―H stretching of water in the higher energy region. The acidity of the catalyst was measured by FT-IR using pyridine as the diagnostic base. The BET surface area measurements indicated the surface areas between 900 and 1000 m2 g−1 and pore diameters around 26 Å units. The catalytic activity of the materials was tested for the vapour phase esterification of acetic acid with n-butyl alcohol (NBA), isobutyl alcohol (IBA) and tertiary butyl alcohol (TBA) under autogeneous condition at 100, 150, 175 and 200 °C. NBA conversion was found to be higher than IBA and TBA. The hydrophobic properties of catalyst, alcohols and the stearic properties of alcohols were suggested to play important roles in the esterification. Al-MCM-41 (25) for NBA, Al-MCM-41 (100) for IBA and TBA was found to be more active. The mechanism was Eley–Rideal type. The reaction was also studied over commercially available heteropolyacids and zeolites (HM, Hβ, HZ and ZSM-5). Except for zeolites, other catalysts were found to have nearly identical activity to that of Al-MCM-41. Zeolites showed less activity for NBA and TBA but comparable activity to IBA. The requirement of Brönsted acid sites for the reaction was clearly established by running the reaction in the absence of catalyst. Occurrence of the reaction mainly within the pores was confirmed by running the reaction over the as-prepared catalyst that provides less conversion than the calcined material.
Keywords: Comparison; Esterification; Al-MCM-41; Acetic acid; n-Butyl alcohol; Isobutyl alcohol; Tertiary butyl alcohol;
Gas-phase hydrogenation of acetonitrile over Pt and Pt–Pd supported on mesoporous solids: influence of the metallic precursor by M.C. Carrión; B.R. Manzano; F.A. Jalón; I. Fuentes-Perujo; P. Maireles-Torres; E. Rodríguez-Castellón; A. Jiménez-López (34-42).
Gas-phase hydrogenation of acetonitrile has been chosen as a test reaction to evaluate the catalytic behaviour of supported bimetallic catalysts prepared from dinuclear complexes precursors. Thus, Pd/Pt supported on zirconium doped mesoporous silica catalysts, with total metal loading of 1 and 2 wt.%, have been obtained by incipient wetness impregnation by using [PdPtCl2(μ-dppm)2], after removing the ligands by calcination and subsequent reduction with H2. These catalysts have been compared with supported platinum or palladium/platinum catalysts with similar metal loadings prepared from classical inorganic salts ([Pt(NH3)4](NO3)2, PdCl2 and H2PtCl6·6H2O). The metal-based catalysts have been characterized by powder XRD, adsorption–desorption of N2 at 77 K, TEM, H2-TPR and NH3-TPD. A remarkable high degree of metal dispersion was attained when using the dinuclear precursor, giving rise to the highest yield of triethylamine in the gas-phase hydrogenation of acetonitrile, with a selectivity toward this tertiary amine close to 100%.
Keywords: MCM-41; Dinuclear complex; Platinum; Bimetallic catalyst; Mesoporous solid; Hydrogenation of acetonitrile;
Biphenyl hydrogenation over supported transition metal catalysts under supercritical carbon dioxide solvent by Norihito Hiyoshi; Chandrashekhar V. Rode; Osamu Sato; Masayuki Shirai (43-47).
Catalytic hydrogenation of biphenyl to bicyclohexyl, an organic hydrogen storage medium, was examined over supported transition metal catalysts in supercritical carbon dioxide solvent. The yield of bicyclohexyl was almost 100% over the charcoal-supported rhodium (Rh/C) and ruthenium (Ru/C) catalysts at the temperature of 323 K, which was much lower than that required for biphenyl hydrogenation in organic solvents (573 K). The initial activity was higher over the Rh/C catalyst, while the initial selectivity to bicyclohexyl was higher over the Ru/C catalyst. The conversion of biphenyl increased with increase in hydrogen and carbon dioxide pressures, while the selectivity to bicyclohexyl was independent of hydrogen and carbon dioxide pressures over both catalysts.
Keywords: Supercritical carbon dioxide; Hydrogenation; Biphenyl; Charcoal-supported rhodium catalyst; Charcoal-supported ruthenium catalyst; Bicyclohexyl; Hydrogen storage;
Decomposition of ethylene carbonate in the presence of ionic liquid-based zinc tetrahalide catalysts by Hoon Sik Kim; Palgunadi Jelliarko; Je Seung Lee; So Young Lee; Honggon Kim; Sang Deuk Lee; Byoung Sung Ahn (48-52).
A series of ionic liquid-based zinc tetrahalide complexes were synthesized and their effects in the coupling reactions of ethylene oxide (EO) and carbon dioxide to produce ethylene carbonate (EC) were evaluated. The zinc tetrahalide complexes displayed high catalytic activities for the coupling reaction, but were found to cause a severe decomposition of EC during the vacuum-distillation of the product mixture. Among the various factors affecting the EC decomposition, the concentration of zinc tetrahalide species was most responsible for the decomposition: the lower the concentration, the lesser the decomposition. The addition of an imidazolium or ammonium halide was effective for enhancing the activity of the zinc tetrahalide complex while having only a minor effect on the decomposition rate. The optimum catalyst composition was discussed for producing EC feasibly with minimized product decomposition.
Keywords: Ionic liquid-based zinc tetrahalide; Coupling reaction; Ethylene carbonate decomposition; Zinc tetrahalide species;
Preparation of Cr2O3-promoted copper catalysts on rice husk ash by incipient wetness impregnation by Feg-Wen Chang; Wen-Yao Kuo; Hsien-Chang Yang (53-61).
Rice husk ash (RHA) was utilized as the support material for manufacturing Cr2O3-promoted copper catalyst by incipient wetness impregnation. With constant copper loading at 15 wt%, the effects of Cr content varying from 0 to 5 wt% on surface properties and catalytic activity were investigated. In addition to RHA, commercial silica gel was also used as catalyst support for comparison to study the effect of support material. Surface characterizations were examined extensively by XRD, TPR, SEM, N2 sorption, and H2–N2O titration, while catalytic activities were studied using ethanol dehydrogenation. The results indicate that copper dispersion is enhanced by the initial increase in Cr2O3 promoter content up to 2 wt%, while it then deteriorates gradually upon further increase in promoter content. It has been suggested that an optimal Cr content around 2 wt% not only enhances catalytic activity but also retards catalyst deactivation. Generally speaking, catalyst deactivation results predominantly from copper sintering. Despite the lower BET surface area, RHA is superior to commercial silica gel as a candidate for catalyst support in this work, because the surface of the former may possess more unique pores, while the majority of surface pores on the latter are interconnected and thus can be clogged easily.
Keywords: Rice husk ash; Silica support; Chromia promoter; Copper catalyst; Ethanol dehydrogenation; Incipient wetness impregnation;
The effect of cavitating ultrasound on the aqueous phase hydrogenation of cis-2-buten-1-ol and cis-2-penten-1-ol on Pd-black by R.S. Disselkamp; K.M. Denslow; T.R. Hart; J.F. White; C.H.F. Peden (62-66).
We have studied the effect of cavitating ultrasound on the heterogeneous aqueous hydrogenation of cis-2-buten-1-ol (C4 olefin) and cis-2-penten-1-ol (C5 olefin) on Pd-black to form the trans-olefins (trans-2-buten-1-ol and trans-2-penten-1-ol) and saturated alcohols (1-butanol and 1-pentanol, respectively). Silent (and magnetically stirred) experiments served as control experiments. As described in an earlier publication by our group, we have added an inert dopant, 1-propanol, in the reaction mixture to ensure the rapid onset of cavitation in the ultrasound-assisted reactions that can lead to altered selectivity compared to silent reaction systems [R.S. Disselkamp, Ya-Huei Chin, C.H.F. Peden, J. Catal. 227 (2004) 552]. The motivation for this study is to examine whether cavitating ultrasound can reduce the [trans-olefin/saturated alcohol] molar ratio during the course of the reaction. This could have practical application in that it may offer an alternative processing methodology of synthesizing healthier edible seed oils by reducing trans-fat content. We have observed that cavitating ultrasound results in a [(trans-olefin/saturated alcohol)ultrasound/(trans-olefin/saturated alcohol)silent] ratio quantity less than 0.5 at the reaction mid-point for both the C4 and C5 olefin systems. This indicates that ultrasound reduces trans-olefin production compared to the silent control experiment. Furthermore, there is an added 30% reduction for the C5 versus C4 olefin compounds again at reaction mid-point. We attribute differences in the ratio quantity as a moment of inertia effect. In principle, the C4 versus C5 olefins has a ∼52% increase in moment of inertia about C2＝C3 double bond slowing isomerization. Since seed oils are C18 multiple cis-olefins and have a moment of inertia even greater than our C5 olefin here, our study suggests that even a greater reduction in trans-olefin content may occur for partial hydrogenation of C18 seed oils.
Keywords: Cavitating ultrasound; Hydrogenation; Isomerization; Edible oils;
Oxidation characteristics of Ru/CeO2 catalyst by Saburo Hosokawa; Satoshi Nogawa; Makoto Taniguchi; Kazunori Utani; Hiroyoshi Kanai; Seiichiro Imamura (67-73).
Oxidation characteristics of Ru/CeO2 were investigated by N2O decomposition in the presence of C3H6, by temperature programmed desorption (TPD), IR, and XAFS measurements using C3H6 as a probe molecule. Ru/CeO2 (Ru: 5 wt%) had highly dispersed Ru species which formed Ru―O―Ce and Ru＝O bonds. This Ru species was in the five-coordination environment and reacted rapidly with allylic hydrogen of C3H6, providing its double bond oxygen. The Ru＝O site was easily regenerated under oxygen atmosphere. This type of metal-oxo species was not formed for Pt, Pd, and Rh on CeO2. The peculiar oxidation property of Ru/CeO2 catalyst was due to the Ru＝O species. The optimal preparation procedure for producing Ru＝O species was to support Ru on hydrated Ce(OH)3 without drying or calcinations. The saturated amount of Ru＝O species was 2 wt% loading of Ru.
Keywords: Ru/CeO2; Ru＝O; N2O decomposition; C3H6; IR; XAFS;
Preparation of S, C cation-codoped SrTiO3 and its photocatalytic activity under visible light by Teruhisa Ohno; Toshiki Tsubota; Yousuke Nakamura; Kazuhiro Sayama (74-79).
S, C cation-codoped strontium titanium dioxide (SrTiO3) was synthesized by calcination of a mixture of thiourea and SrTiO3 powders in a lidded crucible. After C and S ions were doped into SrTiO3, the absorption edge of SrTiO3 powder was greatly shifted from 400 to 700 nm. The obtained powder was found by XPS, XRD and FT-IR to have a perovskite structure in which C and S atoms were incorporated into SrTiO3. S and C doping improved the photocatalytic activity of the doped SrTiO3 for oxidation of 2-propanol. Under a wide range of light irradiation at wavelengths longer than 350 nm, the photocatalytic activity levels of C, S cation-codoped SrTiO3 were about two times higher than those of pure SrTiO3. We found that a new absorption edge was formed in the visible light region due to doping of S and C atoms. The formation of this new absorption edge might be the reason for the high level of visible-light photocatalytic activity of this substance.
Keywords: Strontium titanate; Visible light activity; Photocatalyst; Doping of S cation; Doping of C cation; Utilization of solar light;
Selective synthesis of bisphenol F catalyzed by microporous H-beta zeolite by Suman K. Jana; Takeshi Okamoto; Tsuyoshi Kugita; Seitaro Namba (80-85).
The bisphenol F synthesis from the liquid-phase phenol and formaldehyde condensation reaction in the presence of water over microporous H-beta zeolites, with different Si/Al ratios, has been investigated. The catalysts have been characterized for their phase purity and acidity. With an increase in the aluminum content in beta zeolite, the acidity is increased gradually; however, the catalytic activity is increased and passes through a maximum. Among the different Al-containing beta zeolites (having Si/Al ratios from 11.5 to 124.5 mol mol−1), the catalyst with Si/Al ratio of 75.0 mol mol−1 shows the best catalytic performance in the bisphenol F synthesis process. The influences of catalyst amount, phenol/formaldehyde ratio and reaction temperature on the phenol and formaldehyde condensation over the catalyst showing the highest bisphenol F activity have been thoroughly studied.
Keywords: H-beta; Zeolite; Bisphenol F; Phenol; Formaldehyde;
A comprehensive comparison of CH4-CO2 reforming activities of NiO/Al2O3 catalysts under fixed- and fluidized-bed operations by Xin Chen; Kazunori Honda; Zhan-Guo Zhang (86-97).
The fixed- and fluidized-bed CH4-CO2 reforming activities of Ni-based catalysts were systematically compared in an identical micro quartz reactor that can operate in either fixed- or fluidized-bed mode. Results demonstrated the superiority of fluidized-bed over that fixed-bed for the title reaction. Two commercial catalysts and one self-prepared Ni-based catalyst were tested first at the specific reforming conditions of a furnace temperature of 1073 K, a CO2/CH4 molar ratio of 1.5 and SV of 93,750 ml/(h g) to confirm that the superiority of fluidized-bed was independent of catalyst. A series of comparative tests over the self-prepared NiO/γ-Al2O3 catalyst followed at various conditions: the furnace temperatures of 997–1173 K, the CO2/CH4 ratios of 1.0–2.5 and SVs of 25,000–187,500 ml/(h g). After we identified the superiority of fluidized-bed reforming at all but equilibrium-controlling conditions, two fixed- to fluidized-bed mode-switching reforming tests with the NiO/γ-Al2O3 catalyst were conducted to provide decisive proof for the stated finding. In parallel, thermo-gravimetric analysis (TG), temperature programmed oxidation (TPO) and reduction (TPR) techniques were also applied to characterize the spent samples and then to elucidate the superiority of fluidized-bed reforming. Consequently, the TG and TPO results revealed that the amount of carbon deposited over the NiO/γ-Al2O3 catalyst was always less under the fluidized-bed operation than the amount in the fixed-bed reforming, whereas TPR experiments depicted that the catalyst reduction was significantly improved under the fluidized-bed operations. Moreover, experimentally, special attention was paid to measuring the actual reforming temperatures and the results showed that the bed temperatures of the fluidized-bed reforming were always unexpectedly lower than those of the fixed-bed reforming. Thus, carbon removal through C-CO2 reaction in the oxidative regions and the catalyst reduction in the reductive zones of the fluidized-bed are proposed to explain its carbon deposition-suppressing and catalyst reduction-improving effects and then its higher reforming performances.
Keywords: CH4-CO2 reforming; Ni-based catalyst; Fluidized-bed; Carbon deposition;
Decomposition of trifluoromethane over nickel pyrophosphate catalysts containing metal cation by Hiroaki Onoda; Takafumi Ohta; Jun Tamaki; Kazuo Kojima (98-103).
Nickel pyrophosphates containing metal cations were prepared from aqueous solutions. The obtained phosphates were characterized with inductively coupled plasma (ICP), differential thermal analyses (DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), specific surface area, acid strength, amount of acidic sites, and adsorbed carbon measurements. The phosphates were used as a catalyst for decomposition of trifluoromethane. The kinds and ratios of metal cation added were discussed. The nickel pyrophosphate catalysts containing magnesium had higher selectivity to CO2 and longer lifetimes than aluminum orthophosphate for decomposition of trifluoromethane.
Keywords: Decomposition of trifluoromethane; Nickel pyrophosphate; Metal cation addition; Catalytic lifetime;
Influence of acidity and pore geometry on the product distribution in the hydroisomerization of light paraffins on zeolites by Rafael Roldán; Francisco J. Romero; Cesár Jiménez-Sanchidrián; José M. Marinas; Juan P. Gómez (104-115).
Several platinum supported zeolites with different topologies [beta (SiO2/Al2O3 = 25, 75, 150), USY(60), mordenite(20, 90), ferrierite(55) and ZSM-5(80)] have been tested as catalysts for the hydroisomerization of n-hexane, cyclohexane and n-heptane. Pt/BETA(25) provided the best results to convert C6 and C7 with high conversion and selectivity to isomers. The distribution of monobranched and multibranched isomers with different sizes is influenced by the specific pore opening of each catalyst. All the samples showed an insufficient metal sites to acid sites ratio, which promoted cracking as a consequence of further reactions of monobranched and multibranched isomers in the acid sites. The transformation of 1-hexene was compared to that of n-hexane to evaluate the effects of a higher intermediate alkene concentration. Considerations regarding n-hexane cracking mechanisms were also done. These unbalanced bifunctional catalysts promote the dimerization-cracking mechanism. In fact, this was the prevailing cracking mechanism rather than classical β-scission for all the samples except for Pt/BETA(25), for which some explanations are given. Our results suggest that the conversion is an acidity dependent parameter, whereas the selectivity only depends on the conversion obtained for each catalyst and therefore it cannot be controlled by tailoring the catalyst acidity. By comparison of different reactions performed by either the pure alkanes or their mixtures, cyclohexane was found to act as an inhibitor. However, no changes in the product distribution were observed.
Keywords: Supported-metal catalysts; Zeolites; Isomerization; Cracking mechanism; Beta-scission; Dimerization; n-Hexane; n-Heptane; Cyclohexane; 1-Hexene;
CuO/CeO2 catalysts: Redox features and catalytic behaviors by Xiaolan Tang; Baocai Zhang; Yong Li; Yide Xu; Qin Xin; Wenjie Shen (116-125).
The reduction and oxidation features of nanostructured CuO/CeO2 catalysts prepared by the deposition–precipitation method were extensively investigated by TPR, FT-IR and in situ XPS techniques. Both the chemical states of copper and the reduction degree of ceria could be well controlled during the reduction with hydrogen by adjusting the temperature. Noticeably, the fully reduced Cu0 could be further oxidized into Cu+ in hydrogen by increasing the reduction temperature through the interaction between Cu0 and lattice oxygen of ceria immigrating to the surface. Structure–reactivity relationship was established between the structural features of CuO/CeO2 formed during the pre-reduction with hydrogen and its catalytic activities for CO oxidation. It was observed that reduction with hydrogen at 473–573 K, which leads to the full presence of metallic copper in the catalyst, gives rise to higher CO conversion. These phenomena were interpreted in terms of the reduction degrees of ceria, the changes of surface morphology and the chemical states of copper species. The interface oxygen activation as well as its transfer from the interface to the adsorbed reactant was found to play decisive roles in determining the reaction rate of CO oxidation.
Keywords: CuO/CeO2; Redox features; Chemical states; Metal–support interaction; CO oxidation;
Mechanistic study of a new low-temperature methanol synthesis on Cu/MgO catalysts by Ruiqin Yang; Yi Zhang; Yuki Iwama; Noritatsu Tsubaki (126-133).
In situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) was used to clarify the reaction mechanism of a new methanol synthesis method on a Cu/MgO catalyst at 443 K from syngas containing CO2 using an ethanol promoter. The adsorbed formate species were formed by exposing Cu/MgO catalyst to syngas (CO/CO2/H2), and it reacted easily with ethanol to form ethyl formate in two states: gas-phase species and physisorbed species, at low temperature. The ethyl formate was the reactive intermediate, and it was reduced easily by hydrogen atoms on Cu to form methanol at low temperature. The reaction temperature was significantly decreased due to the promotional catalytically active action of ethanol. This is a new reaction route, as ethanol used in this reaction was not consumed due to its self-regeneration by hydrogenation of ethyl formate. In order to accelerate this reaction, one must introduce a large amount of ethanol into the reaction system.
Keywords: In situ DRIFT; Methanol; Cu/MgO; Syngas (CO/CO2/H2); Ethyl formate;
Catalytic cracking of C4 alkenes to propene and ethene: Influences of zeolites pore structures and Si/Al2 ratios by Xiangxue Zhu; Shenglin Liu; Yueqin Song; Longya Xu (134-142).
Catalytic cracking of butene to propene and ethene was carried out in a continuous plug-flow stainless steel reactor over various zeolites with different pore structures and Si/Al2 ratios. It was found that the porous structure and acidity of zeolites play important roles in the zeolite performance in the butene cracking process. The smaller the pore size of the zeolite catalysts, the higher the initial selectivities towards propene and ethene and the lower the initial selectivities to C3–C4 alkanes. This is attributed to a suppression of the hydrogen transfer reaction of the alkenes. Although high initial selectivities to propene and ethene could be gained on medium-pore zeolites of ZSM-22, ZSM-23, ZSM-35 and on small-pore zeolite SAPO-34, the stabilities of all these zeolites were poor. On the other hand, due to its special structure characteristic, the ZSM-5 zeolite exhibited the best stability in the catalytic cracking of butene among the tested zeolites. MCM-22 also presented a better catalytic performance. Besides the pore structure, the acidity, which was influenced by the Si/Al2 ratio of the zeolite, was another important factor affecting the performance of the zeolites. By increasing the Si/Al2 ratio of the ZSM-5 zeolite, the selectivities to propene and ethene and the stabilities were remarkably increased owing to a suppression of secondary reactions.
Keywords: Butene; Propene; Ethene; Catalytic cracking; Zeolite catalysts;
Hydrogen production via steam–iron reaction using iron oxide modified with very small amounts of palladium and zirconia by Kohei Urasaki; Naoshi Tanimoto; Taito Hayashi; Yasushi Sekine; Eiichi Kikuchi; Masahiko Matsukata (143-148).
We investigated hydrogen production by the steam–iron reaction using iron oxide modified with very small amounts of palladium and/or zirconia at a temperature of 723 K and under atmospheric pressure. Reduction of iron oxide with hydrogen and oxidation of partially reduced iron oxide with steam (Fe3O4 + 4H2 ↔ 3Fe + 4H2O) were repeated in the range of reduction degree of 30–50 mol%. Changes in the weight of the samples were monitored using a tapered element oscillating microbalance (TEOM) to control the degree of reduction. Unmodified iron oxide caused significant deactivation due to sintering with increasing number of redox cycles. The addition of a very small amount (0.23 mol%) of palladium or zirconia onto the surface of the iron oxide enhanced the reduction and/or oxidation of the partially reduced iron oxide, which suppressed sintering. Palladium accelerated both the reduction and oxidation rates of partially reduced iron oxide, while zirconia increased only the oxidation rate. Addition of both palladium and zirconia together to the iron oxide resulted in marked enhancement of both reduction and oxidation.
Keywords: Iron oxide; Redox; Hydrogen; Palladium; Zirconia;
Catalytic cracking of n-octane over alkali-treated MFI zeolites by Je Sik Jung; Ji Won Park; Gon Seo (149-157).
The catalytic cracking of n-octane over alkali-treated MFI zeolites was studied to investigate the catalytic roles of acidity and pore structure in the catalytic cracking of naphtha. The alkali treatment on the MFI zeolite induced the dissolution of silica and alumina, resulting in the loss of strong acid sites and the formation of mesopores. The low acidity and short residence time induced the reduction of cracking activity, lowering the conversion and enhancing the selectivity for primary cracking products. The alkali treatment, therefore, shows the cracking path of n-octane in zeolite pores. The acidity was the predominant factor in determining the conversion level and product composition, so a high conversion and a high yield of alkene were obtained over the MFI zeolite with a large amount of strong acid sites. Mesopores formed during the alkali treatment suppressed the production of longer alkanes such as hexane and heptane by reducing further oligomerization. The alkali treatment was not effective in enhancing overall alkene selectivity, but the selectivity for propene was high over alkali-treated zeolites, due to the rapid elution of primary cracking products.
Keywords: Catalytic cracking; n-Octane; MFI zeolite; Alkali treatment;
Catalytically active and selective centers for production of ɛ-caprolactam through liquid phase Beckmann rearrangement over H-USY catalyst by Chawalit Ngamcharussrivichai; Peng Wu; Takashi Tatsumi (158-168).
Heterogeneously catalyzed Beckmann rearrangement of cyclohexanone oxime to ɛ-caprolactam over H-ultrastable Y (USY) zeolite, with the SiO2/Al2O3 ratio of 7, has been extensively studied under liquid-phase conditions using benzonitrile (PhCN) as solvent. Although the oxime conversion reached as high as 98%, a satisfactory selectivity to the lactam was not attained due to a rapid increase in the formation of cyclohexanone as a hydrolysis product. Direct addition of a small amount of water to the reaction mixture before heating retarded the hydrolysis of oxime reactant, resulting in a remarkable improvement in the lactam selectivity to 94%. It is believed that an energetically preferential adsorption of water on the oxime-hydrolysis sites and acid-catalyzed hydrolysis of PhCN are the important keys for a selective production of ɛ-caprolactam. The FTIR spectroscopic studies on adsorbed PhCN have suggested that weak Brønsted acid sites are the active and selective sites for the Beckmann rearrangement, whereas the cyclohexanone formation is mainly catalyzed on Lewis acid sites.
Keywords: Beckmann rearrangement; Benzonitrile; USY; Acid sites;
Hydrogen production by partial oxidation and reforming of DME by Qijian Zhang; Xiaohong Li; Kaoru Fujimoto; Kenji Asami (169-174).
Hydrogen production by catalytic partial oxidation and reforming of DME was successfully carried out at an ambient pressure and 600–750 °C. An H2 yield of more than 90% was obtained with little methane production over Pt/Al2O3 and Ni-MgO combined catalysts. Ni-MgO was active for the reforming of DME as well as for the reforming of CH4, which formed through a homogeneous reaction between DME and oxygen. The hybrid catalyst gave a better performance than the dual-bed ones. High temperature and high W/F were favorable to H2 yield by improving the reforming reaction.
Keywords: DME; Partial oxidation; Reforming; Hydrogen production;
Selective oxidation of alcohols in a continuous multifunctional reactor: Ruthenium oxide catalysed oxidation of benzyl alcohol by Dmitry V. Bavykin; Alexei A. Lapkin; Stan T. Kolaczkowski; Pawel K. Plucinski (175-184).
A multifunctional compact reactor was designed, built, and tested, using as a model reaction the selective oxidation of benzyl alcohol to benzaldehyde with molecular oxygen. The reactor contains static mixers, heat-transfer channels and mm-scale packed-bed reaction channels, i.e., integrating mixing, heat transfer and reaction functionalities. Integrated compact reactor technology should be particularly attractive to the fine chemistry and pharmaceutical industries. The reactor was shown to operate in the kinetic regime over a broad range of operating conditions due to intensified mass transfer. The reactor was also shown to operate isothermally despite high reaction rate, an appreciable heat effect and high reactant concentration (TOF = 300 h−1, Δ H r ° = − 183.7 kJ mo l − 1 ). Staged injection of oxygen along the length of the reactor was investigated as a method of increasing the selectivity of oxidation reactions. Staged injection was shown to be beneficial; however, this was likely to be due to the development of a more uniform hydrodynamic regime of two-phase flow along the packed reaction channel. Experiments were performed with the ruthenium(III) hydrated oxide catalyst supported on alumina (0.9 wt% Ru/Al2O3). High activity and selectivity were observed even when working with reactant concentrations approaching industrial conditions (1 mol L−1).
Keywords: Multifunctional reactors; Structured reactors; Selective oxidation; Ruthenium oxide; Compact reactors; Three-phase;
Rare-earth elements modified hydrotalcites and corresponding mesoporous mixed oxides as basic solid catalysts by R. Bîrjega; O.D. Pavel; G. Costentin; M. Che; E. Angelescu (185-193).
The inspection of a series of hydrotalcites (HTs) samples prepared under different supersaturation conditions, has allowed the selection of the low supersaturation method conducting to a more disordered HT structure as appropriate to accommodate rare-earth elements (REE) species in HTs structures. The goal is to prepare mesoporous mixed oxides to be used as catalysts for basic catalyzed organic reactions. A series of REE (Y3+, Dy3+, Gd3+, Sm3+, La3+) modified HTs samples are prepared under low supersaturation conditions. Their derived mixed oxides were obtained by the thermal decomposition of HTs at 460 °C for 18 h under argon flow. The properties of HTs modified REE and of their corresponding mixed oxides are analyzed from XRD structural data, textural measurements and basicity data. The HTs modified REE in an amount of approximately 10% (w/w), from 6.78% (w/w) for Mg0.75Al0.23Y0.02 to 11.74% (w/w) for Mg0.75Al0.23Dy0.02 proved to be effective precursors for the manufacturing of mixed oxides catalysts very active and selective in the reaction of cyanoethylation of ethanol with acrylonitrile. A relation between their conversions and their properties, in particular, the number of weak and medium-strength basic sites could be proposed.
Keywords: REE modified HTs; Mg(Al/REE)O mixed oxides; Cyanoethylation of ethanol with acrylonitril;
Molecular traffic control in porous nanoparticles by Andreas Brzank; Gunter Schütz (194-202).
We investigate the conditions for reactivity enhancement of catalytic processes in porous solids by use of molecular traffic control (MTC) as a function of reaction rate and grain size. With dynamic Monte-Carlo simulations and continuous-time random walk theory applied to the low concentration regime we obtain a quantitative description of the MTC effect for a network of intersecting single-file channels in a wide range of grain parameters and for optimal external operating conditions. The efficiency ratio (compared with a topologically and structurally similar reference system without MTC) is inversely proportional to the grain diameter. However, for small grains MTC leads to a reactivity enhancement of up to approximately 30% of the catalytic conversion A → B even for short intersecting channels. This suggests that MTC may significantly enhance the efficiency of a catalytic process for small porous nanoparticles with a suitably chosen binary channel topology.
Keywords: Molecular traffic control; Nanoparticle; Zeolite; Master equation; Discrete poisson equation;
Pd nanoparticles introduced inside multi-walled carbon nanotubes for selective hydrogenation of cinnamaldehyde into hydrocinnamaldehyde by Jean-Philippe Tessonnier; Laurie Pesant; Gabrielle Ehret; Marc J. Ledoux; Cuong Pham-Huu (203-210).
Palladium nanoparticles (4–6 nm) were deposited inside multi-walled carbon nanotubes (MWNTs) via a simple impregnation using an aqueous solution containing a palladium salt. The low surface tension of the solvent allows a complete filling of the tube, leading, after thermal treatments, to the formation of small and homogeneous palladium particles decorating the inner cavity of the support. The impregnation method was extremely efficient as no palladium particle located on the outer surface of the tubes was observed. The catalyst was tested for the selective hydrogenation of cinnamaldehyde which contains both a C＝C and a C＝O bond. The nanotubes based catalyst exhibits along with a high catalytic activity an extremely high selectivity towards the C＝C bond hydrogenation when compared to a commercial catalyst supported on a high surface area activated charcoal. A peculiar metal-support interaction and the absence of micropores and of oxygenated surface groups on the carbon nanotubes support are proposed to explain these results.
Keywords: Carbon nanotubes; Palladium nanoparticules; Cinnamaldehyde hydrogenation;
Formation of methyl methacrylate by condensation of methyl propionate with formaldehyde over silica-supported cesium hydroxide catalysts by Mamoru Ai (211-215).
The vapor-phase aldol condensation of methyl propionate (MP) with formaldehyde (HCHO) to form methyl methacrylate (MMA) was studied with a HCHO/MP molar ratio of 0.2, using formalin as a source of HCHO over solid base catalysts. Cesium hydroxide was the best base catalyst and silica gel was the sole compound effective as the support. The optimum Cs/Si atomic ratio was in the range of 2.0/100 to 2.5/100. Na cations present in the silica gel as an impurity decreased the yield of MMA. The addition of water into the reaction feed did not affect the selectivity, though the reaction rate decreased a little. With an increase in the HCHO/MP molar ratio, the yield increased, but the selectivity decreased. The catalytic activity decreased very slowly with the time-on-stream. The deactivated catalyst was completely regenerated by calcinations in air at 400 °C.
Keywords: Methyl methacrylate formation; Vapor-phase aldol condensation; Cesium hydroxide; Methyl propionate; Formaldehyde;
Synthesis of Al-containing octahedral molecular sieves and oxidation of cyclohexane with them by Takanori Miyake; Kenjirou Koike; Isao Aoki; Norihiro Murayama; Makoto Sano (216-219).
An octahedral molecular sieve composed of Mn, Mg and O is known as todorokite. Here, synthesis of todorokite containing Al in its framework was studied and its formation by the hydrothermal method was, for the first time, confirmed by combining the results of ICP, XRD and TEM. There existed a limitation to the amount of Al that could be incorporated into the structure, probably because of the cation-to-cation repulsion in the channel. The oxidation of cyclohexane with tert-butyl hydroperoxide was studied as a model reaction. Results revealed that Al-containing todorokite and proton-exchanged Al-containing todorokite promoted the reaction to cyclohexyl alcohol and cyclohexanone.
Keywords: Octahedral molecular sieve; Todorokite; Manganese; Hydrothermal synthesis; Oxidation; Cyclohexane;
Mg–Fe–Al mixed oxides with mesoporous properties prepared from hydrotalcite as precursors: Catalytic behavior in ethylbenzene dehydrogenation by Yoshihiko Ohishi; Tomonori Kawabata; Tetsuya Shishido; Ken Takaki; Qinghong Zhang; Ye Wang; Kiyoshi Nomura; Katsuomi Takehira (220-231).
Supported iron catalyst was prepared from Mg–Fe–Al hydrotalcite-like compounds as precursors and successfully applied for the ethylbenzene dehydrogenation to styrene. After the calcination, the iron-substituted hydrotalcite-like samples were converted to mixed oxides with a high surface area as well as a mesoporous character; the XRD analysis indicates the formation of periclase Mg(Fe, Al)O as a main phase. Catalytic tests of the Mg2Fe x Al1−x catalysts showed that the styrene conversion increased with increasing the iron content up to x = 0.75 and then decreased, while the selectivity was the highest at x = 0.25. The optimum temperature for the reaction was 550 °C, which was lower than that used in the commercial process. No favorable effect of the addition of either CO2 or O2 in the reaction medium was observed in this reaction. Actually, the pre-treatment with H2 resulted in an increase in the activity at the beginning of the reaction as well as a stable activity during the reaction. The ethylbenzene conversion of 60% and the styrene selectivity of 95% were kept for 3 h over Mg3Fe0.5Al0.5 catalyst at 550 °C. After the reaction for 3 h, the iron species on the catalyst was partially reduced to the valence state between Fe2+ and Fe3+. The high catalytic performance can probably be attributed to the formation of partially reduced iron oxides on the surface of catalyst and to the high surface area along with the porous structure, which originated from the Mg–Fe–Al hydrotalcite structure in the precursors.
Keywords: Mg–Fe–Al hydrotalcite-like materials; Ethylbenzene dehydrogenation; The reduced iron oxide; Porous catalyst;
Characterization of reduced α-alumina-supported nickel catalysts by spectroscopic and chemisorption measurements by G. Poncelet; M.A. Centeno; R. Molina (232-242).
Ni/α-Al2O3 catalysts, prepared from nickel acetylacetonate, with low nickel contents (0.4–3 wt.%), have been characterized after a reduction treatment at 400 and 550 °C by infrared spectroscopy of adsorbed CO (IR-CO), X-ray photoelectron spectroscopy (XPS), hydrogen chemisorption measurements, and temperature-programmed reduction (TPR). Relatively high dispersion and particle size smaller than 8 nm were established. It was observed that an increase of the metal loading resulted in an enhancement of the average particle size and a decrease of the dispersion, indicating that suppression of hydrogen adsorption encountered in supported nickel catalysts with low metal contents is not necessarily due to the amount of nickel as reported in the literature, but instead, can be explained in terms of change of the particle size.
Keywords: Nickel acetylacetonate; Alumina; Dispersion;
Erratum to “Bulk oxidation state of the different cationic elements in the MoVTe(Sb)NbO catalysts for oxidation or ammoxidation of propane” [Applied Catalysis A: General 279 (2005) 67–77] by Manuel Baca; Jean-Marc M. Millet (243).