Surface Heterogenity of Bismuth-Molybdate Catalyst in Oxidative Dehydrogenation of Olefin

Abstract

The oxidative dehydrogenation of C₄, C₅ olefins over bismuth molybdate catalyst has been investigated by a flow method and a pulse technique. The isomers of pentene were found to be less reactive than those of corresponding butenes in the case of using the flow method, but the reverse result was obtained by means of a pulse technique. The activation energy of the reaction obtained by the former was much larger than that of the latter. The value of activation energy obtained by the pulse technique varied from 11kcal•mol^-1 to 23kcal•mol^-1 with the amount of isoprene added to the pulse of 1-butene. It was found that the reaction was strongly inhibited by isoprene added. The heat of adsorption of olefins and dienes was also measured by the gaschromatographic method.
From these results, it was suggested that the active sites of bismuth molybdate catalyst were ununiformity. The pulse reaction proceeded on the strong active sites which were inhibited by the products in the flow reaction, and the mild active sites which had a similar activity were only effective for the flow reaction.