Effects of valence states of iron in iron phosphates on the catalytic activity in oxidative dehydrogenation of isobutyric acid

Abstract

Oxidative dehydrogenation of isobutyric acid to methacrylic acid was studied over an iron phosphate catalyst with a P/Fe atomic ratio of 1.2. The freshly prepared catalyst consisting of Fe³⁺ is reduced with isobutyric acid to iron(II) pyrophosphate [Fe₂P₂O₇] via a bluish black intermediate. Under the reaction conditions, the fresh catalyst is reduced gradually to the intermediate and the Fe₂P₂O₇ is also reoxidized to the intermediate. However, both the catalytic activity and the selectivity were scarcely affected with a large variation in the valence states of iron in the bulk of iron phosphate. On the other hand, the studies on the reaction in the absence of oxygen revealed that the reaction is promoted by the redox cycle of iron phosphate.