Moessbauer study of ferric phosphate catalysts

Oxidative dehydrogenation (OCD) Pb-FePO4 and Ag-FePO4 catalysts were investigated by using Moessbauer spectroscopy. The values of the isomer shifts and quadrupole splittings show that the iron atoms are present as high-spin ferric ions Fe3+, which are location in two non-equivalent lattice sites A and B. In the first catalyst the peak area ratio A/B = 1, and in the second catalyst, A/B > 1. When the catalysts contacts isobutylic acid (IBA), the Fe3+ at site A reduced to Fe2+, and the Fe3+ at site B atoms keeps unchanged. After DXD reaction for 500hr, very little have remained at site A. Thus, these Moessbauer studies demonstrate that site A is catalytic active center during the OXD reaction of IBA. (orig.)