It has been suggested that the activity and selectivity in catalytic oxidation of hydrocarbons over an oxide catalyst are related to the metal-oxygen bond strength. Sachtler proposed that selective catalysts have high rates of change of this bond energy with the degree of reduction of the oxide. Other correlations are found in the literature. We have measured the heat of oxidation of vanadium oxide supported on γ-Al2O3 as a function of the degree of reduction (DR) of the oxide by calorimetry. It was found that the heat increased rapidly as the degree of reduction increased, as did the rate of oxidation. However, the rate of reduction of the oxide was only a weak function of DR. When the catalytic properties of these samples in butane oxidation were tested using the pulse method, it was found that the selectivity changed rapidly with DR: the higher DR is, the higher is the selectivity for dehydrogenation. The selectivity also depended on the loading of vanadium oxide on the support. The sample of a higher loading was less selective and produced oxygenated as well as dehydrogenation products and carbon oxides. The sample of a lower loading produced only dehydrogenation products and carbon oxides. This difference in product selectivity was also observed in the steady state reaction. These results will be discussed with respect to the metal-oxygen bond strength and the nature of the vanadia species in the samples.
|Number of pages
|American Chemical Society, Division of Petroleum Chemistry, Preprints
|Published - Apr 1 1992
ASJC Scopus subject areas
- Fuel Technology