Characteristics of iron phosphate and its catalytic activity for oxidative dehydrogenation of isobutyric acid

Article abstract of DOI:10.1246/bcsj.69.509

In the absence of oxygen, P/Fe = 1.2 catalyst samples are reduced by hydrogen or isobutyric acid to form Fe₂P₂O₇ via Fe₃(P₂O₇)₂, while the P/Fe= 1.0 samples are reduced directly to Fe₂P₂O₇; without passing through Fe₃(P₂O₇)₂. Fe₂P₂O₇ is oxidized by air to an unknown compound (Y-phase), but not to Fe₃(P₂O₇)₂ nor FePO₄. The Y-phase is reduced to Fe₂P₂O₇. During the use in the oxidative dehydrogenation of isobutyric acid, freshly calcined catalysts are reduced to Fe₃(P₂O₇)₂, while the Fe₂P₂O₇ catalysts are oxidized to Y-phase, though the rates are very slow. The catalytic activity and selectivity are scarcely affected by variation in the structure of the iron phosphate catalyst and in the oxidation states of iron ions. The P/Fe and Fe²⁺(Fe²⁺+Fe³⁺) ratios on the surface, which were measured from cooled catalyst samples, are almost the same as those in the bulk.