ACIDIC PROPERTY AND OXIDATION ACTIVITY OF MOO3-V2O5-P2O5 TERNARY OXIDES

The relationship between the acid-base properties and the oxidation activity of a series of ternary oxide catalysts, MoO3-V2O5-P2O5, with different V/Mo composition and a constant phosphorus content, P/(Mo+V) = 0.1, was investigated. The acidity was determined by means of the NH3 adsorption and by studying the catalytic activity for acid-catalyzed reactions, such as dehydration of isopropyl alcohol and isomerization of 1-butene, in the presence of an excess of air. A new acidic site is generated by the combination of two binary oxides, i.e., MoO3-P2O5 and V2O5-P2O5, and a broad maximum in the acidity occurs at V/(Mo-j-V) = 0.4-0.9. The basic property is so small that no satisfactory data can be obtained from the adsorption of acidic molecules such as CO2, SO2, and acetic acid. The catalysts, regardless of composition, are inactive for reactions which are accelerated by basic sites, such as oxidative dehydrogenation of isopropyl alcohol to acetone, oxidative decomposition of formic acid to CO2, and oxidation of methanol to CO2. The oxidation activities for butadiene and methanol can be tied to the acidity of the catalysts.