Molybdenum Oxide Catalysts Research Articles

The oxidation of propene over bismuth oxide, molybdenum oxide and bismuth molybdate catalysts: III. Electrical conductivities of bismuth molybdate, MoO 3 and Bi 2O 3

On exposure to propene, 1-butene or hydrogen, pressed discs of the catalysts bismuth molybdate and molybdenum oxide show rapid and reproducible increases of electrical conductivity at temperatures between 400 and 550 °C. The conductivities decrease to their original values on reoxidation by gaseous oxygen. At any selected stage of reduction or reoxidation, the rates of reduction or reoxidation are linear functions of the gas pressures. If the gases are removed at a given extent of reduction, the conductivities then change with temperature as expected for semiconductors, and the energy gaps fall to very low values on moderately-reduced catalysts. In the presence of an excess of a 1:1 mixture of propene and oxygen, bismuth molybdate shows a nearly constant conductivity corresponding to roughly 10% reduction, and this extent of reduction varies only slightly as the proportions of propene and oxygen are changed from 9:1 to 1:9. With 1:1 mixtures of the gases molybdenum oxide appears to be reduced to only a very small extent. Bismuth oxide shows an initial decrease of conductivity followed by an increase when contacted with propene, and the conductivity falls on reoxidation.

The ESR of the oxygen adsorbed on supported vanadium pentoxide

A detailed study of the methanol chemisorption and oxidation processes on oxide surfaces allowed the development of a method to quantify the number of surface active sites (Ns) of metal oxide catalysts. In situ infrared analysis during methanol adsorption showed that molecular methanol and surface methoxy species are co-adsorbed on an oxide surface at room temperature, but only surface methoxy species are formed at 100°C. Thermal stability and products of decomposition of the adsorbed species were determined with temperature programmed reaction spectroscopy (TPRS) experiments. Controlled adsorption with methanol doses resulted in a stable monolayer of surface methoxy species on the oxide surfaces. The stoichiometry of methanol chemisorption resulted in one surface methoxy adsorbed per three Mo atoms for polymerized surface molybdenum oxide structures, regardless of surface molybdenum oxide coordination. The activity of the catalysts per surface active sites (turnover frequencies — TOF) was calculated in order to quantitatively compare the reactivity of a series of monolayer supported molybdenum oxide catalysts. The TOF value trends reflect the influence of the bridging Mo–O–Support bond and the electronegativity of the metal cation of the oxide support.

Oxidation of Propylene over Vanadium and Molybdenum Oxide Catalysts

The oxidation of propylene with a large amount of propylene has been studied over vanadium and molecule oxide catalysts in a flow system. The relation temperature was 470°C; the partial pressure of oxygen was kept at 0.1 atm, while that of propylene was varied from 0.1 to 0.8 atm. The main oxidation products were carbon monoxide, carbon dioxide, and acrrolein. In the oxidation with a pure vanadium oxide catalyst, the yield of acrolein increased with the proplene partial pressure, and the selectivity to acrolein was about 30% at the propylene partial pressure, and the selectivity values of the selectivity to various reaction products at the contact time of 0 sec did not change even though the propylene partial pressure was changed from 0.1 to 0.8 atm. X-ray patterns of the catlyst used (free of carriers) show the presence (of V2O4 or a mixture) of V2O4and V2O3 according to the partial pressure of propylene. It is concluded that acrolein undergoes a secondary reaction more severly when a vanadium oxide catalyst is in the higher oxidative state, that is, when it is richer in V2O4. In the system of vanadium-molybedenum oxides, the three mixed catalysts, containing 10, 18 and 30 mol% moO3, acted in a similar way and raised the selectivity to acroline to some extent in coparison with a pure vanadium oxide catalyst, whatever was partial pressure of propylene. In the mixtures containing more than 50 mol% MnO3, MoO3 had a dilution effect on the catalytic activity. A pure molybenum oxide catalyst scarcely oxidized propylene at all 470°C. It has thus been found that the catalytic cativity of this system is closely related with the formation of solid solutions MoO3 in V2O5.

Magnetic Study of Cobalt Molybdenum Oxide Catalysts

Magnetic Study of Cobalt Molybdenum Oxide Catalysts

Studies on the catalytic Synthesis of Cyano benzenes. I.

A vapor phase catalytic reaction between toluene and ammonia in the presence of molybdenum oxide and vanadium oxide, respectively, was investigated. The activityfor formation of benzonitrile was better in molybdenum oxide carrying catalystt but the selectivity for benzonitrile was superior in vanadium oxide carrying catalyst. The activity of vanadium oxide-alumina catalyst did not change during the experimental period of about 10 hours, but that of molybdenum oxide-alumina catalyst decreased with the time of reaction: however, it was regenerated by the heating in air. A preliminary treatment of vanadium oxide catalyst in an atmosphere of ammonia at 550°c showed practically no change in the activity of catalyst, but that of molybdenum oxide catalyst showed considerable decrease in its activity. It was considered to be mainly due to the formation of lower oxide by the reduction of molybdenum oxide in this reaction atmosphere. It was found that the acidity of catalyst carrier was injurious, as by the action of alumina gel or silicagel of acidic nature on molybdenum oxide, the formation of benzene was accele rated. The catalyst with sintered alumina carrier treated at 1200°c was effective por to inhbit the formation of benzene as a by-product and to improve the selectivity formation of benzonitrile. It was indicated that the rate determining step was before the formation of benzylamine, that the formation of benzonitrile from benzylamine with molybdenum oxide catalyst was proceeded mainly through dehydrogenation process, and that the benzonitrile formation with vanadium oxide catalyst was proceeded mainly through disproportionation.

On the question of applying chromium oxide and molybdenum oxide catalysts to obtain crystalline poly‐α‐olefins

AbstractThis article gives experimental data concerning the dependence of polymerization efficiency of chromium oxide catalyst upon the methods of preparation and reports on the character of the polymerization efficiency. The polyethylene and polypropylene obtained in this process of polymerization is characterized by high quality. Besides chromium oxide catalyst, molybdenum oxide catalyst with added lithium hydride was studied.

Physical Properties of Promoted Molybdenum Catalysts

THE addition of small quantities of promoters to molybdenum oxide catalysts is known to prod striking changes in their activity for hydrocarbon decomposition1. These effects have been related to differences in their capacity for the chemisorption of hydrocarbons at or near the reaction temperature2; but no fundamental reason for these observations was found.

Molybdenum oxide catalysts for the reduction of phenol to benzene

Molybdenum oxide catalysts for the reduction of phenol to benzene

Promoter Concentration and Catalysis

IN a recent publication1 attention has been directed to the critical concentration of silica required to give the maximum increase in the activity of molybdenum oxide catalysts used in the decomposition of hexane at 500°. A survey has now been made of the concentration required with a wide range of other promoters, and it is found that in the case of oxides of sodium, chromium, cerium, aluminium, barium, boron and thorium, the ratio of the number of atoms of these elements to 100 atoms of molybdenum is the same as that previously observed with silicon.