Role of Lewis and brønsted sites in selective oxidation of propene on MoO3–Sb2O4catalyst

Abstract

A relationship between activity and acidity of MoO3–α-Sb2O4 catalysts for selective propene oxidation was established. It was found that two types of acid sites existed on the mixed oxides containing MoO3, i.e. the Lewis sites which are probably situated on the (010) face, and the Bronsted sites on the (001), (101) and (100) faces of MoO3 crystallites. No acidity could be detected on pure α-Sb2O4, but its presence in the mixture could increase the Bronsted acidity and decrease the Lewis acidity. A linear correlation between the propene conversion and the number of Lewis sites was obtained. On the other hand, the yield of acrolein from propene depended on the number of Bronsted sites. Test results suggest that the chemisorption of propene takes place on the Lewis sites, and the subsequent abstraction of α-hydrogen, which is the rate-determining step for the selective oxidation of propene, is accomplished on the Bronsted sites.