scispace - formally typeset
Search or ask a question

Showing papers on "Dehydrogenation published in 1993"


Journal ArticleDOI
TL;DR: In this paper, a modified ZSM-5 zeolite catalysts with a fixed bed continuous-flow reactor and with a temperature programmed reactor were used for the de-hydrogenation and aromatization of methane.
Abstract: The dehydrogenation and aromatization of methane on modified ZSM-5 zeolite catalysts has been studied under non-oxidizing conditions with a fixed bed continuous-flow reactor and with a temperature programmed reactor. The results show that benzene is the only hydrocarbon product of the catalytic conversion of methane at high temperature (973 K). The catalytic activity of ZSM-5 is greatly improved by incorporating a metal cation (Mo or Zn). H2 and ethene have been directly detected in the products with a mass spectrometer during TPAR. A carbenium ion mechanism for the activation of methane is suggested.

738 citations


Book
01 Apr 1993
TL;DR: Acylation of aromatic compounds alkylations, dealkylations, transalkylation, disproportionations halogenations nitrations miscellaneous substitution reactions addition reactions elimination reactions oxidation, dehydrogenation reactions aromatization hydrogenation, hydrogenolysis cyclization reactions Diels-Alder reactions isomerization, oxidative dimerization rearrangements condensation reactions thermal and hydrolytic decompositions reactions of carbonyl compounds reactions of carboxylic acids and derivatives amino acid and peptide formation under prebiotic conditions miscellaneous reactions.
Abstract: Acylation of aromatic compounds alkylations, dealkylations, transalkylations, disproportionations halogenations nitrations miscellaneous substitution reactions addition reactions elimination reactions oxidation, dehydrogenation reactions aromatization hydrogenation, hydrogenolysis cyclization reactions Diels-Alder reactions isomerization dimerization, oxidative dimerization rearrangements condensation reactions thermal and hydrolytic decompositions reactions of carbonyl compounds reactions of carboxylic acids and derivatives amino acid and peptide formation under prebiotic conditions miscellaneous reactions.

278 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the steam reforming of methanol over a Cu/ZnO/Al 2 O 3 catalyst and found that the reaction yields carbon dioxide and hydrogen in the ratio of one to three, with small amounts of dimethyl ether and carbon monoxide being produced at high conversion.
Abstract: The steam reforming of methanol over a Cu/ZnO/Al 2 O 3 catalyst has been investigated. The reaction yields carbon dioxide and hydrogen in the ratio of one to three, with small amounts of dimethyl ether and carbon monoxide being produced at high conversion. Comparison of the rates of methanol dehydrogenation and of steam reforming over the same catalyst indicate that steam reforming proceeds via dehydrogenation to methyl formate. Methyl formate then hydrolyses to formic acid which decomposes to carbon dioxide and hydrogen. Detailed studies of the kinetics of the reactions show that methanol dehydrogenation controls the rate of steam reforming. Langmuir-Hinshelwood modelling indicates that hydrogen extraction from adsorbed methoxy groups is rate determining to the overall processes.

249 citations


Journal ArticleDOI
TL;DR: In this article, the authors studied the catalytic properties of catalytic oxidations of a wide range of products ranging from alkenes, dienes, anhydrides, acids, and carbon oxides.

214 citations


Journal ArticleDOI
TL;DR: In this paper, the physical and chemical state of reduced Ga using in-situ X-ray absorption at the Ga K-edge was investigated, showing that reduced Ga is present in highly dispersed form without Ga nearest neighbors, probably as a monomeric hydride species coordinated to basic oxygens within zeolite channels.

205 citations


Journal ArticleDOI
TL;DR: In this article, the influence of preparation methods of V-Mg-O catalysts on their catalytic properties in the oxidative dehydrogenation of propane has been studied.

194 citations


Journal ArticleDOI
TL;DR: In this paper, a variety of oxide-based catalysts have been prepared, characterised, and tested in the oxidative dehydrogenation reaction and it has been found that with these catalysts, the maximum selectivity to propene at a specific conversion of propane is never higher than can be obtained in the absence of a catalyst.
Abstract: The pyrolysis and the oxidative dehydrogenation of propane have been investigated in a quartz reactor. It has been found that by optimising the propane/air ratio it has been possible to obtain very high yields of propene and ethene. A variety of oxide-based catalysts have been prepared, characterised, and tested in the oxidative dehydrogenation reaction. It has been found that with these catalysts, the maximum selectivity to propene at a specific conversion of propane is never higher than can be obtained in the absence of a catalyst. The results also show no obvious correlation between catalytic properties and the presence of specific crystalline phases. It is suggested that lower than optimum selectivities to propene may arise because of the presence in the catalysts of small, but undetected, amounts of pure V 2 O 5 . Comparison with other published work suggests that there is an upper limit on the yield of propene which can be obtained for a purely heterogeneously catalysed reaction. A combination of homogeneous and heterogeneous contributions to the oxidative dehydrogenation reaction may provide a means of obtaining even higher yields of propene.

109 citations


Journal ArticleDOI
TL;DR: In this paper, the steady-state rates of carbon formation on a silica-supported Ni-Cu catalyst exposed to CH4 + H2 gas mixtures have been measured for a range of gas compositions (partial pressure of methane, 20-80 kPa, and of hydrogen, 5-15 kPa) and temperatures in the range 723-863 K.

108 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used molybdenum-vanadium-niobium oxide catalysts in the temperature range of 350-450 °C for the oxidative dehydrogenation of ethane.
Abstract: The oxidative dehydrogenation of ethane has been studied at atmospheric pressure using molybdenum-vanadium-niobium oxide catalysts in the temperature range of 350–450 °C. The presence of all three oxides together is necessary in order to have active and selective catalysts. The best results have been obtained using a mixture having a Mo ∶ V ∶ Nb ratio of 19 ∶ 5 ∶ 1. Our studies of the variation of oxide composition suggest that the active phase is based on molybdenum and vanadium. Niobium enhances the intrinsic activity of the molybdenum-vanadium combination and improves the selectivity by inhibiting the total oxidation of ethane to carbon dioxide. The apparent activation energies for the conversion of ethane to ethylene, carbon monoxide and carbon dioxide were 18, 27 and 17 kcal/mol, respectively. The addition of water vapor to the gas stream does not affect the product distribution on this catalyst.

95 citations



Journal ArticleDOI
TL;DR: The surface chemistry of methyl groups adsorbed on Pt(111) has been studied using TPD and reflection-adsorption infrared spectroscopy (RAIRS) as discussed by the authors.

Journal ArticleDOI
TL;DR: In this paper, the authors used a hydrogen-permeable membrane reactor for the de-hydrogenation of isobutane to isomethomethane, which was conducted in a comparatively low-temperature range (from 623 to 723 K).
Abstract: The dehydrogenation of isobutane to isobutene was conducted in a comparatively low-temperature range (from 623 to 723 K) using a hydrogen-permeable membrane reactor. An Al2O3-supported platinum catalyst exhibited high activity compared with a commercial Cr2O3-Al2O3 catalyst in a conventional flow reactor. In the membrane reactor, however, the platinum catalyst gave a lower yield of isobutene than the Cr2O3-Al2O3 catalyst, although the isobutene yields on both of these catalysts were high compared with thermodynamic equilibrium values attained in a conventional reactor. The platinum catalyst deteriorated more rapidly in the membrane reactor, due to deposition of carbonaceous material. On the other hand, undesirable side reactions such as hydroisomerization and hydrogenolysis were suppressed in the membrane reactor due to the removal of hydrogen produced from the reaction side, leading to high selectivity for isobutene. The yield of isobutene in the membrane reactor increased by the addition of tin to Pt/Al2O3, due to the suppression of coke formation.

Journal ArticleDOI
TL;DR: In this article, the results showed that under optimum conditions the non-catalysed reaction can be very efficient and selective, achieving a conversion of 45% at a selectivity of 73.7%, corresponding to a percentage yield of ethene of 33% and a space-time yield of 15.8 mmol/cm3 h.
Abstract: The oxidative dehydrogenation of ethane to ethene has been studied in a quartz reactor in the absence and in the presence of a range of MgO-based catalysts using a variety of gas compositions over a range of temperatures. The results show that under optimum conditions the non-catalysed reaction can be very efficient and selective. At a temperature of 600°C, using an ethane/air ratio of 1:2, a conversion of 45% was achieved at a selectivity of 73.7%, corresponding to a percentage yield of ethene of 33% and a space-time yield of ethene of 15.8 mmol/cm3 h. It was observed that none of the catalysts tested under comparable conditions gave such high yields. Reasons for this difference are discussed. Comparison with published results on the catalytic oxidative dehydrogenation of ethane suggest that the non-catalysed gas-phase reaction is competitive with the best available catalysts.

Journal ArticleDOI
TL;DR: In this article, results of a study of the propane dehydrogenation reaction in a membrane reactor utilizing a sol-gel alumina membrane for feed mixtures containing significant amounts of propylene and hydrogen were presented.

Journal ArticleDOI
TL;DR: In this article, a comparison of the acidic properties of a series of metal polyoxocation pillar interlayered clay minerals (M-PILCs) was made by studying the infrared spectra of adsorbed pyridine.

Journal ArticleDOI
TL;DR: In this paper, the reaction of formic acid on the surface of yttria-stabilized zirconia was studied using temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS).
Abstract: The reaction of formic acid on the (100) surface of yttria-stabilized zirconia was studied using temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). Formic acid absorbed molecularly at temperatures below 200 K and dissociated upon heating to room temperature to produce absorbed formate an hydroxyl. Dehydration to CO was the primary pathway for decomposition of absorbed formates. In addition to the dehydration pathway, a fraction of the adsorbed formates underwent dehydrogenation to CO 2 . Formaldehyde was also detected as a minor product

Journal ArticleDOI
TL;DR: In this article, the photocatalytic reaction of neat alcohols (ethanol or 2-propanol) by metal-loaded titanium(IV) oxide (TiO2) was conducted under argon at room temperature.
Abstract: The photocatalytic reaction (excitation wavelength, greater than 300 nm) of neat alcohols (ethanol or 2-propanol) by metal-loaded titanium(IV) oxide (TiO2) was conducted under argon at room temperature. The dehydrogenation products hydrogen (H2) and acetaldehyde (or acetone in the case of 2-propanol) were found in the absence of additives. The corresponding acetals, ethers, and alkanes were obtained by the addition of concentrated hydrochloric acid (HCl). The measurement of the product yields during the post-irradiation dark reaction in the presence of photocatalyst (TiO2) loaded with platinum(IV) oxide (PtO2) revealed that the production of ether and ethane and the regeneration of ethanol proceed by the hydrogenation of acetal over loaded metal, presumably via a hemiacetal intermediate. X-ray diffraction (XRD) analyses showed that the loaded PtO2 is reduced to platinum metal during the course of the photocatalytic reaction. For the production of ether from HCl-acidified ethanol, Pd-loaded catalysts, especially prepared by precipitation—reduction, exhibit the highest activity of several metal-loaded TiO2 catalysts. From XRD and X-ray photoelectron spectroscopy studies of Pd-loaded TiO2 particles, it was shown that the smaller the size of the Pd particles, the higher the selectivity for ether production from the acidified ethanol suspension. The application of this photocatalytic O-alkylation to the synthesis of cyclic ethers was demonstrated.

Patent
27 Apr 1993
TL;DR: In this paper, the authors proposed a new catalyst composed of reduced and sulfided nickel crystallites on siliceous supports which have been treated with chromium compounds and oxidized to provide surface-anchored chromyl species.
Abstract: Alkanes are dehydrogenated by passage through alternating dehydrogenation zones and selective oxidation zone(s), in which latter zone(s) hydrogen produced in the preceding endothermic dehydrogenation reaction is selectively oxidized to generate heat for the succeeding dehydrogenation reaction. New catalyst compositions are prepared comprising reduced and sulfided nickel crystallites on siliceous supports which have been treated with chromium compounds and oxidized to provide surface-anchored chromyl species. Also new catalyst compositions are prepared by sulfiding nickel-containing compositions with carbonaceous sulfur compounds such as dialkylsulfoxides. Another embodiment of the invention is catalyst and dehydrogenation therewith, in which pores having radius of 50 to 200 Angstroms occupy pore volume from 0.30 to 1.50 ml per gram of the support, and pores having radius of 20 to 50 Angstroms occupy pore volume less than 0.1 ml per gram of the support. In another embodiment, alkanes are dehydrogenated using as catalyst a metal or metal compound having dehydrogenating activity supported on alkali-treated alumina.

Journal ArticleDOI
TL;DR: In this article, the angle of incidence of the electron beam was used to determine the orientation of the adsorbed molecule and the symmetry of the adorbate/surface complex is C3v, which indicates adsorption with the C3 axis of the molecule perpendicular to the surface.

Journal ArticleDOI
TL;DR: In this paper, the deactivation of isobutane was observed within two or three hours on stream and this deactivation intensified with temperature and olefin content but was inhibited by hydrogen.

Journal ArticleDOI
TL;DR: In this article, the influence of various preparation methods on the performance of V-Nb-0 catalysts has been investigated and it was found that the activity and selectivity of a vanadium site depend on the nature of the neighbouring atoms.

Journal ArticleDOI
TL;DR: Polyaniline serves as a synthetic metal catalyst with reversible redox under oxygen to induce dehydrogenative and/or decarboxylative oxidation of benzylamines and 2-phenylglycine into the corresponding imines as discussed by the authors.
Abstract: Polyaniline serves as a synthetic metal catalyst with reversible redox under oxygen to induce dehydrogenative and/or decarboxylative oxidation of benzylamines and 2-phenylglycine into the corresponding imines and, in combination with copper(II) chloride or iron(III) chloride, dehydrogenation of cinnamyl alcohol into cinnamaldehyde possibly due to complexation

Journal ArticleDOI
TL;DR: In this paper, the authors compared the catalytic properties of V/sepiolite and V 2 O 5 /MgO catalysts in the oxidative dehydrogenation of propane.
Abstract: Sepiolite supported vanadium catalysts have been studied in the oxidative dehydrogenation of propane. Different vanadium species are present on the catalysts and the proportion changes with the preparation methods, support modifications, and vanadium content. At low vanadium content, isolated tetrahedral species are formed and both activity and selectivity to propene increase when increasing the vanadium content. At medium or high vanadium content the appearance of associated vanadium species can be observed and, while the activity still increases when increasing total vanadium, the selectivity to propene remains constant. MgV 2 O 6 and V 2 O 5 crystallites are formed at vanadium content higher than 30 wt.% of V 2 O 5 , and, depending on the propane conversion level, the selectivity to propene remains constant or decreases when increasing the vanadium content. On a comparative basis, the oxidative dehydrogenation of propane has also been carried out on a V 2 O 5 /MgO catalyst. From the comparison between catalytic properties in the oxidative dehydrogenation of propane on V/sepiolite and V/MgO catalysts a reaction network has been established and both type of catalysts show the same conversion-selectivity behaviour. The nature of the sites responsible for selective and non-selective oxidation on V/sepiolite catalysts has been proposed.

Patent
Ping Mei1, James B. Boyce1, Richard I. Johnson1, Michael G. Hack1, Rene A. Lujan1 
07 Jun 1993
TL;DR: In this article, a low temperature process for dehydrogenating amorphous silicon using lasers is described, where irradiation at the various energy densities can result in the formation of polysilicon due to melting of the ammorphous silicon layer.
Abstract: A low temperature process for dehydrogenating amorphous silicon using lasers Dehydrogenation occurs by irradiating one or more areas of a hydrogenated amorphous silicon layer with laser beam pulses at a relatively low energy density After the multiple laser pulse irradiation at a relatively low energy density, the laser energy density is increased and multiple irradiation at a higher energy density is performed If after the multiple irradiation at the higher energy density the amorphous silicon hydrogen content is still too high, dehydrogenation proceeds by multiple irradiations at a yet higher energy density The irradiation at the various energy densities can result in the formation of polysilicon due to melting of the amorphous silicon layer As irradiation may be selectively applied to the amorphous silicon, an integral amorphous silicon-polysilicon structure may be formed

Journal ArticleDOI
TL;DR: In this article, the selectivity of the orthovanadates of Mg, Zn, Cr, Ni, Cu and Fe was investigated for butane oxidation at 500°C using a feed of C 4 /O 2 /He of 4/8/88.

Journal ArticleDOI
TL;DR: In this paper, the acid and redox properties of heteropolyacids of the H3+nPVnMo12−nO40 series, both unsupported and supported on the potassium salt K3PMo12O40, were investigated.

Journal ArticleDOI
TL;DR: In this article, a two-dimensional mathematical model was formulated and solved for a catalytic membrane reactor in a tube-and-shell configuration, which correctly predicted the 20% increase in conversion over conventional fixed bed operation, when a permselective alumina membrane was used as the fixed bed reactor tube.

Journal ArticleDOI
01 Jan 1993-Carbon
TL;DR: In this paper, the decomposition of propan-2-ol was studied using carbon catalysts with a different chemical nature of the surface, and it was found that the dehydration occurs on the outer surface of the carbon catalyst, whereas the dehydrogenation takes place also within the catalyst pores.

Journal ArticleDOI
TL;DR: In this article, the same yields of CO2 were observed on all vanadium aluminophosphate catalysts, while the higher the yield of propene the lower the CO is.
Abstract: VAPO-5 and V/ ALPO-5 catalysts have been tested for the oxidative dehydrogenation of propane. Depending on the vanadium contents and the preparation procedure, different vanadium species and different catalytic behavior are observed. The catalyst containing V5+ species with a tetrahedral coordination presents the higher yield of propene in the oxidative dehydrogenation of propane. The same yields of CO2 are observed on all vanadium aluminophosphate catalysts, while the higher the yield of propene the lower the yield of CO is.

Journal ArticleDOI
TL;DR: In this paper, deuterium atoms formed on a hot tungsten filament are impinged onto a Cu(111) surface precovered with cyclohexane, and dehydrogenated products are evolved when the surface is heated in subsequent temperature-programmed reaction (TPR) experiment.
Abstract: Cyclohexane desorbs molecularly intact from Cu(111) and does not react with deuterium atoms that are preadsorbed on the surface By contrast, when deuterium atoms formed on a hot tungsten filament are impinged onto a Cu(111) surface precovered with cyclohexane, dehydrogenated products (cyclohexene, cyclohexadiene, and benzene) are evolved when the surface is heated in a subsequent temperature-programmed reaction (TPR) experiment These D-atom-induced dehydrogenation products provide strong evidence for an Eley-Rideal mechanism where D atoms abstract hydrogen from cyclohexane prior to thermal accommodation with the surface The kinetics of cyclohexene evolution indicate that both single and sequential H-atom abstractions occur by this mechanism