Molybdenum Oxide Catalysts Research Articles

Characterization of molybdenum oxide catalysts supported on anatase and rutile polymorphs of titania by low-temperature oxygen chemisorption

Oxygen chemisorption (at -78°C, reduced state) and methanol oxidation activity have been measured for molybdenum oxide catalysts supported on anatase and rutile modifications of TiO 2 . The resutls suggest that molybdenum oxide forms a monolayer with a high degree of dispersion of the active component. Anatase-supported catalysts show better dispersion and activity than the corresponding rutile-supported ones. A correlation has been found between oxygen chemisorption and activity of the catalysts toward partial oxidation of methanol

Hydroprocessing of substituted benzenes over a sulfided CoO-MoO 33/γ-A1 2O 3catalyst

The performance of titania-supported molybdenum carbide, nitride, phosphide and oxide catalysts was compared for catalytic hydrodeoxygenation (HDO) of phenol. Phenol was selected as a stable model component for lignin degradation products in fast pyrolysis bio-oil. The synthesis and formation path of the materials was evaluated by the use of complementary characterization techniques (XRD, TPR and TGA–MS). All the catalysts showed promising catalytic performance during testing in a fixed-bed reactor set-up at a temperature of 350 °C and total pressure of 25 bar, and the highest activity was achieved with 15 wt% Mo2C/TiO2. A high selectivity towards benzene was observed with all catalysts. MoP supported on TiO2 showed the strongest tendency to aromatic ring hydrogenation and also a significant selectivity (10% level) towards methylcyclopentane, indicating contributions of acidic surface chemistry. Thus, Mo based materials are active and promising materials for establishing selectivity control in HDO of bio-oils.

Supported molybdenum oxide catalyst. Structure and chemistry of oxidized, reduced, and sulfided surfaces.

Highly dispersed molybdena-titania catalyst can be prepared by an equilibrium adsorption method. In this method, molybdate anions adsorb onto positively charged titania surfaces via electrostatic attraction by controlling pH of the impregnating solution. The amounts of absorbed molybdate anion are strongly dependent on pH of the impregnating solution and they increase as an inverse function of pH. XRD, Raman, and XPS data of the calcined samples show that monolayer coverage of molybdenum oxide over-layer possesses a highly distorted MoO6 group with a molecular geometry resembling a distorted square pyramid. The Mo species are fixed by an oxygen bridge with Ti, as Mo-O-Ti, or with neighboring Mo, as Mo-O-Mo.The catalytic oxidation of methanol over the surface molybdate species on titania possess higher turnover numbers and higher selectivities of partial oxidation products than do the catalysts exceeding monolayer coverage which possess the crystalline MoO3 phase. Changes of the surface properties either, after reduction and sulfiding treatment over monolayer catalyst, have also been investigated. The NO chemisorption and XPS studies show that two types of active sites appeared after reduction treatment: one site is active for hydrogenation of 1, 3-butadiene and the other site is active for metathesis of propene. A higher degree of coordinative unsaturations of Mo is required for hydrogenation than for metathesis. After subjecting sulfiding treatments to the catalyst, hydrogenolysis of thiophene requires the ensemble of doubly or triply coordinative unsaturations.

High liquid yields from bituminous coal via hydropyrolysis with dispersed catalysts

In this paper the authors report the results of catalytic hydropyrolysis experiments in which greater than 60% daf coal basis yields of tar are produced with weight ratios of tar to gases up to 80% higher than observed in an uncatalyzed reaction. The work has also shown that dispersed sulfided molybdenum and hydrous titanium oxide (HTO) catalysts coated directly on the coal are superior to Lewis acids and alumina supported hydrogenation catalysts in terms of tar yields achieved and reduction of the amount of light hydrocarbon gases produced. In addition, they have performed two-stage hydropyrolysis tests which demonstrate that the tar produced is readily upgraded.

Segregation and chemical state of vanadium and molybdenum in vanadium—molybdenum oxide catalyst studied by x-ray photoelectron spectroscopy

The vanadium—molybdenum oxide (VMoO) catalyst has been studied by X-ray photoelectron spectroscopy (XPS) and thermal gravimetric analysis. (TGA). The results show that the surface composition of VMoO catalyst strongly depends on temperature. At room temperature, the catalyst surface is usually enriched with molybdenum. When the sample is heated to above 350–400°C, the vanadium species diffuse from bulk to surface; with a rise in temperature, the ratio of vanadium-to-molybdenum gradually increases and the surface even becomes enriched with vanadium. Besides, when the VMoO catalyst is heated to a certain temperature, the sample can absorb or evolve oxygen according to the ambient oxygen partial pressure. During the redox process, the vanadium species in VMoO catalyst are liable to change their chemical state, the V 4+ and V 5+ sites seem to act as the inlet and outlet sites, respectively of oxygen. The function of molybdenum species in VMoO catalyst seems to be to promote the evolution of lattice oxygen and tend to retain the ratio of V 4+-to-V 5+ at a certain value, which may be important for high selectivity and activity of the VMoO catalyst.

Effect of pretreatment conditions on hydrocarbon reactions on alumina-supported molybdenum catalysts

Isomerization and cracking of 2-methylpentane were studied on alumina supported molybdenum oxide catalysts. Before all catalytic experiments, the catalyst was reduced in situ under hydrogen flow. The pretreatment conditions appeared to affect strongly the properties of the catalyst. By lowering the heating rate used to reach the reduction temperature (from 150°C/15 min to 50°C/15 min) or by increasing the reduction duration (from 2 h to 6 h), the catalytic properties could be altered from a high level of isomerization activity to a high level of cracking activity. The nature of the two kinds of catalytically active sites is discussed.

High-resolution electron microscopy of cobalt—molybdenum catalysts structural Changes and Activity

Unsupported cobalt—molybdenum oxide catalyst (atomic ratio of Co: Mo = 1:1) was calcined in air at 723 K, reduced in hydrogen at 673 K and sulphided at 673 K with hydrogen—thiophene mixtures for 10 and 70 min and with hydrogen—hydrogen sulphide for 120 min. High-resolution electron micrographs of the calcined sample show the presence of CoMoO4; this is also the main component detected after reduction, but its crystallinity is poor in the latter instance. MoS2 layers appear after even brief sulphidation. Sulphidation with hydrogen sulphide results in a catalyst covered almost entirely with MoS2, with traces of Co9S8 among its layers. Prolonged sulphidation with hydrogen—thiophene results in segregation of MoS2 and Co9S8 into separate crystallites; also, elemental sulphur appears. The catalytic activity at these stages has been evaluated.

ChemInform Abstract: Homologation, Hydrogenolysis, and Dehydrogenation of Ethane on SiO2‐ and SiO2‐Al2O3‐Supported Reduced Molybdenum Oxide Catalysts.

ChemInformVolume 19, Issue 9 Preparative Organic Chemistry ChemInform Abstract: Homologation, Hydrogenolysis, and Dehydrogenation of Ethane on SiO2- and SiO2-Al2O3-Supported Reduced Molybdenum Oxide Catalysts. A. K. GHOSH, A. K. GHOSH Res. Inst. Catal., Hokkaido Univ., Sapporo 060, Jap.Search for more papers by this authorK. TANAKA, K. TANAKA Res. Inst. Catal., Hokkaido Univ., Sapporo 060, Jap.Search for more papers by this authorI. TOYOSHIMA, I. TOYOSHIMA Res. Inst. Catal., Hokkaido Univ., Sapporo 060, Jap.Search for more papers by this author A. K. GHOSH, A. K. GHOSH Res. Inst. Catal., Hokkaido Univ., Sapporo 060, Jap.Search for more papers by this authorK. TANAKA, K. TANAKA Res. Inst. Catal., Hokkaido Univ., Sapporo 060, Jap.Search for more papers by this authorI. TOYOSHIMA, I. TOYOSHIMA Res. Inst. Catal., Hokkaido Univ., Sapporo 060, Jap.Search for more papers by this author First published: March 1, 1988 https://doi.org/10.1002/chin.198809076AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume19, Issue9March 1, 1988 RelatedInformation

Homologation, hydrogenolysis, and dehydrogenation of ethane on SiO 2- and SiO 2Al 2O 3-supported reduced molybdenum oxide catalysts

Kinetics and reaction mechanisms of homologation, hydrogenolysis, and dehydrogenation of ethane were studied on reduced molybdenum oxides supported on SiO 2 and SiO 2Al 2O 3. It was found that homologation of ethane to propane occurs via (1) dehydrogenation of ethane to ethylene, (2) homologation of ethylene to propylene, and (3) hydrogenation of propylene to propane. The rate-determining step was found to be hydrogenation of adsorbed propylene or that of adsorbed C 2H 5 species with an activation energy of 10.7 kcal/mole. In addition to homologation products, significant amounts of hydrogenolysis and dehydrogenation reaction products were also found. Dehydrogenation of ethane to ethylene had an activation energy of 25 kcal/mole, and it was quite similar to that for desorption of ethylene. Consequently, the dehydrogenation rate was assumed to be controlled by desorption of ethylene formed.

Characterization of titania and zirconia supported molybdenum oxide catalysts by low temperature oxygen chemisorption

Low temperature oxygen chemisorption (LTOC) has been applied to characterize a series of TiO2 and ZrO2 supported Mo-oxide catalysts. The monolayer coverage of the surface is completed when the Mo loading reaches 6% and 4% on the TiO2 and ZrO2 supports, respectively. The results are explained with the help of a “Patch” model of the Mo-oxide phase.

Interaction of isobutene and methacrolein with silica‐supported uranium and molybdenum oxide catalysts

AbstractThe adsorption of isobutene (in the temperature range 309–341K) and methacrolein (in the temperature range 296–336 K) on a Mo/(Mo+U)=0.89 catalyst were studied. The equilibrium data were analysed according to Freundlich's model. The high coverages observed at lower temperatures suggest some participation of physical adsorption in the reversible adsorption. Entropy calculations showed that these adsorbed species are best described by a mobile model which assumes bidimensional translation and two rotational degrees of freedom. Isobutene is weakly chemisorbed, producing reversible species which were identified as a π‐complex formed by interaction with surface OH groups through π‐electrons (infrared bands at 1655, 1615, 1470 and 1375 cm−1), and only a small fraction of isobutene interacts strongly via lattice oxygen forming intermediate species in the oxidation reaction. However, in the presence of oxygen at 523 K a majority of the surface species are strongly held by the surface (infrared bands at 1775, 1723, 1610, 1460 and 1350 cm−1 associated to a methacrylic complex and bands at 1590 and 1538 cm−1 of carbonate‐carboxylate species).

Characterization of silica‐supported uranium–molybdenum oxide catalysts

AbstractThe techniques of X‐ray diffraction, infrared and electron spin resonance spectroscopies, kinetics of reduction by H2, and XPS were used to investigate the chemical species present at the interface in silica‐supported uranium–molybdenum oxide catalysts. In this catalyst series, with constant MoO3 loading (16.7 wt%) and Mo/(Mo + U) atomic ratios ranging between 1 and 0, it was found that the oxidic forms of Mo and U were not well dispersed, MoO3 crystallites being detected on the catalysts with a high Mo/(Mo + U) atomic ratio. In the less‐uranium‐rich catalysts [Mo/(Mo + U) = 0.89] both MoO3 crystallites and a crystalline ‘uranyl molybdate’ phase were present. This catalyst exhibited the highest reduction degree by H2 and the highest ESR signal intensity of Mo5+ ions when reduced under very mild conditions. The information obtained with these techniques was used to explain the promotional effect of U on the MoO3/SiO2 base catalyst for the selective oxidation of isobutene.

Photocatalytic oxidation of propane by oxygen on supported [formula omitted] catalysts

Propane photocatalytic oxidation on silica gel-supported molybdenum oxide catalysts has been investigated. The catalysts prepared via impregnation and Mo(π-C 3H 5) 4 fixation do not exhibit significant differences in their electronic spectra and photocatalytic behavior. The results indicate that photocatalytic activity cannot be related specifically to isolated Mo 6+ ions in tetrahedral coordination and that other surface sites play an important role in photooxidation reactions. Depending on the molybdenum loading, two different domains of photocatalytic activity are observed. At molybdenum loadings below 2 wt% acetone predominates among the partial oxidation products whereas aldehydes are the most abundant at higher loadings. This change in product distribution has been attributed to a change in the nature of the radical intermediates formed in the initiating step depending on the nature and coordination symmetry of the participating Mo ions. The acetone dominating region may be related to the formation of propoxy (C 3H 7O) radicals in contrast to the aldehyde region which is associated with the formation of propyl (C 3H 7) radicals. The characteristics of the sites responsible for these two different behaviors have been suggested with reference to the electronic spectra of these catalysts.

ChemInform Abstract: CATALYTIC CONVERSION OF ALCOHOLS. COMPARISON OF ALUMINUM AND MOLYBDENUM OXIDE CATALYSTS

Chemischer InformationsdienstVolume 14, Issue 20 Preparative Organic Chemistry ChemInform Abstract: CATALYTIC CONVERSION OF ALCOHOLS. COMPARISON OF ALUMINUM AND MOLYBDENUM OXIDE CATALYSTS B. H. DAVIS, B. H. DAVISSearch for more papers by this author B. H. DAVIS, B. H. DAVISSearch for more papers by this author First published: May 17, 1983 https://doi.org/10.1002/chin.198320088AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume14, Issue20May 17, 1983 RelatedInformation

Mechanism of propanol and 1,2-epoxypropane formation in propene oxidation over oxide catalysts

CD2=CHCH3 was oxidized over silica supported molybdenum and vanadium oxide catalysts. The location of deuterium in the by-products propanol and 1,2-epoxypropane indicates that their formation proceeds through an attack of the carbon-carbon double bond in propene, and that 1,2-epoxypropane is an intermediate in the formation of propanol.

Preparation of supported vanadium and molybdenum oxide catalysts using metal acetylacetonate complexes

Supported vanadium and molybdenum oxide catalysts were prepared by reaction of the corresponding acetylacetonate complex in a non-aqueous solution with the surface hydroxyl groups of the carrier. Continuous or batch adsorption of the metal acetylacetonate from toluene, as well as wet impregnation from ethanol, resulted in a uniform coverage of the support. The applied metal oxide was probably present on the surface as a monomolecular dispersion. When readsorption or reimpregnation from toluene was carried out with TiO 2 as support, metal oxide crystallites were formed, which could readily be detected with laser Raman spectroscopy. Reimpregnation from ethanol led to a complete occupancy of the surface hydroxyl groups of the carrier without the formation of metal oxide multilayers or crystallites.

Catalytic conversion of alcohols: XXI. Comparison of aluminum and molybdenum oxide catalysts

Molybdena, as a very selective dehydration catalyst, resembles alumina. Neither catalyst causes isomerization of the initial gas-phase alkene dehydration products. This was confirmed by adding a similar alkene to an alcohol reactant. However, molybdena produced products from some alcohol reactants that even required methyl migrations. For example, dehydration of 4,4-dimethyl-2-pentanol with molybdena produced primarily β-elimination products, whereas the isomeric 2,2-di-methyl-3-pentanol produced only about 10% β-elimination with the remaining dehydration products requiring isomerization by methyl migration. On the basis of alkene distributions from cyclic and acyclic alcohols, molybdena catalyzes dehydration by an E-1-like mechanism in contrast to the concerted mechanism for alumina.

Disproportionation of α-olefins by activated molybdenum oxide catalysts : G. I. Startseva, S. V. Kir'yakova, P. Ye. Matkovskii, M. P. Gerasina and Kh.-M. A. Brikenshtein, Neftekhimiya 23, No. 1, 48–54, 1983

Disproportionation of α-olefins by activated molybdenum oxide catalysts : G. I. Startseva, S. V. Kir'yakova, P. Ye. Matkovskii, M. P. Gerasina and Kh.-M. A. Brikenshtein, Neftekhimiya 23, No. 1, 48–54, 1983

Oxidation of acrolein to acrylic acid on vanadium molybdenum oxide catalyst; The reaction kinetics

The oxidation kinetics of acrolein have been studied in gas phase in the presence of vanadium molybdenum oxide catalyst. Using a through-flow apparatus with integral reactor, the effect has been studied of concentration of individual reaction components, i.e. acrolein, oxygen, steam and acrylic acid, on conversion degree of acrolein. The measurements have been carried out at atmospheric pressure. For evaluation of the kinetic data measured an equation has been suggested expressing dependence of the oxidation rate on the mentioned parameters.

ChemInform Abstract: MECHANISM OF 1‐BUTENE OXIDATION IN CONNECTION WITH THE LAYERED STRUCTURE OF BISMUTH MOLYBDENUM OXIDE (BI2MOO6) CATALYST

Chemischer InformationsdienstVolume 12, Issue 34 Preparative Organic Chemistry ChemInform Abstract: MECHANISM OF 1-BUTENE OXIDATION IN CONNECTION WITH THE LAYERED STRUCTURE OF BISMUTH MOLYBDENUM OXIDE (BI2MOO6) CATALYST H. MIURA, H. MIURASearch for more papers by this authorY. ARAI, Y. ARAISearch for more papers by this authorK. SUGIYAMA, K. SUGIYAMASearch for more papers by this authorT. MATSUDA, T. MATSUDASearch for more papers by this author H. MIURA, H. MIURASearch for more papers by this authorY. ARAI, Y. ARAISearch for more papers by this authorK. SUGIYAMA, K. SUGIYAMASearch for more papers by this authorT. MATSUDA, T. MATSUDASearch for more papers by this author First published: August 25, 1981 https://doi.org/10.1002/chin.198134104Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume12, Issue34August 25, 1981 RelatedInformation