The role of mobile oxygen species in the selective oxidation of isobutene

Abstract

A simple experiment can introduce this contribution: SB{sub 2}O{sub 4} particles on the one hand, and SnO{sub 2} particles on the other hand, are prepared independently, and then mixed at room temperature. A comparison of the methacrolein yields in isobutene oxidation over identical weights of mixtures of different compositions indicates a dramatic synergy: for adequate proportions (Sb{sub 2}O{sub 4}/(Sb{sub 2}O{sub 4} + Sno{sub 2}) = 0.3-0.6) the yield is multiplied by a factor of ten, compared to the added yields which would be reached with the corresponding weights of the simple oxides, if isolated. There is no indication of formation of any mixed phase during the catalytic experiments. All industrial oxide catalysts used for selective catalytic oxidation are composed of more than one phase. The above mentioned results suggest that there is a fundamental reason for that. But the majority of the fundamental studies have dealt with single phases and all the published mechanisms consider phenomena taking place in a single phase. The factors influencing activity and selectivity which are considered are those corresponding to the characteristics of this single phase. Our objective was to investigate the role of external phases.