Mössbauer study of ferric phosphate catalysts

Oxidative dehydrogenation (OXD) Pb−FePO4 and Ag−FePO4 catalysts were investigated by using Mossbauer 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 Mossbauer studies demonstrate that site A is catalytic active center during the OXD reaction or IBA.