PARTIAL OXIDATION OF METHANOL ON MOLYBDENUM AND VANADIUM OXIDE CATALYSTS

Date of Completion

January 1983

Keywords

Engineering, Chemical

Degree

Ph.D.

Abstract

High surface area MoO(,3) and V(,2)O(,5) prepared by the flame method have been studied in regards to the partial oxidation of methanol. The transient response method, with on-line mass spectrometric analysis of the gas phase, yielded enough qualitative-quantitative information to construct a mechanistic model of the reaction.^ Methanol adsorbed reversibly and irreversibly on both oxides under 373(DEGREES)K. Over 403(DEGREES)K the reversible undissociated fraction was negligible. The irreversible chemisorption involved O-H bond scission yielding a methoxy group and an H atom. Under reducing conditions the latter incorporated into the lattice which became a bronze precursor. In the presence of oxygen H formed water.^ The degree of reduction of the oxides affected profoundly their catalytic properties. Adsorption capacity increased with reduction, suggesting that oxygen vacancies were the sites for irreversible chemisorption. Low degrees of reduction favored formaldehyde and CO while intermediate degrees of reduction enhanced dimethylether on MoO(,3) or methylal on V(,2)O(,5). Deep degrees of reduction without oxygen in the gas phase depressed activity due to strong adsorption of surface intermediates.^ In general, selectivity for formaldehyde was better for V(,2)O(,5) than for MoO(,3) when the oxides were not very much reduced. But MoO(,3) showed a higher resistance to poisoning and selectivity decay than V(,2)O(,5). Selectivity for dehydrogenation products was enhanced by the presence of oxygen in the gas phase.^ Under catalysis conditions, in the presence of oxygen, reoxidation was faster than reduction and the degree of reduction of both oxides was limited to less than 6% of a monolayer. In this situation, selectivity for formaldehyde was the highest. ^

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