Synthesis of methacrylic acid by selective oxidation of isobutane, catalysed by Keggin-type polyoxometalates: relationship between catalytic performance, reaction conditions and chemical-physical features of the catalyst

The ammonium salt of 12-molybdophosphoric acid, (NH4)(3)PMo12O40 (polyoxome talate, POM), having the Keggin-type structure was prepared and tested as a . heterogeneous catalyst for the selective oxidation of isobutane to methac rylic acid. This reaction might represent an alternative to the current ind ustrial process for methyl methacrylate production, the acetone-cyanohydrin process, which is characterized by a no longer acceptable environmental im pact. The POM catalyst was found to operate with higher selectivity at isob utane-rich conditions (26 % isobutane, 13 % oxygen), than at isobutane-lean conditions (1 % isobutane, 13 % oxygen). This was attributed to the develo pment of a more favourable distribution of reduced Mo5+ and oxidized Mo6+ s ites in the POM in the former case. Modifications occurring in the catalyst during time-on-stream at different reaction conditions are discussed. (C) 2000 Academie des sciences / Editions scientifiques et medicales Elsevier S AS.