Effects of Acid-Base Properties of MoO3-Bi2O3-P2O5 Catalysts on Oxidation Activity and Selectivity

The vapor-phase oxidation of cis-2-butene, 1, 3-butadiene, acetic acid, and hydrogen were carried out over various MoO3-Bi2O3-P2O5 catalysts with different Bi2O3 contents. Oxidation activity is compared with dehydration activity for 2-propanol, and the ratios of (dehydrogenation rate)/(dehydration rate) for 2-propanol which were used as measures of acidity and basicity of the catalysts. The acidity of the catalysts increases with an increase in the Bi2O3 content and attains a maximum at about Bi/(Mo+Bi)=0.1. The basicity is very low for Bi2O3-poor composition, but sharply increases, with an increase in Bi2O3 at Bi/(Mo+Bi)>0.5. It has been found that oxidation and isomerization activities for olefins are associated with acidity of the catalyst and that oxidation activity for acidic compounds and activation and adsorption of oxygen are associated with basicity. Selectivity for olefin oxidation is also discussed from the viewpoint of the acid-base nature of the reactant and catalyst.