Phase transformations of the FePO4 catalyst in the oxidative dehydrogenation to form an alkyl methacrylate

A phase specific iron orthophosphate catalyst, FePO₄, was synthesized and subjected to oxidative dehydrogenation reactions to form an alkyl methacrylate. The phases of the catalyst, before and after the reactions, were characterized by Mössbauer spectroscopy. The Mössbauer spectra show the change of the catalyst precursor FePO₄, tridymite-like phase (tdm), to the reduced form, iron(II) pyrophosphate, Fe₂P₂O_7, and thereafter the phase change is governed by the temperatures of oxidation. X-ray diffraction and Mössbauer measurements on the spent catalyst, after using organic and water co-feeds, show a transformation of the catalyst to a mixture of phases which are condition specific.