OXIDATIVE DEHYDROGENATION OF ISOBUTYRIC ACID - CHARACTERIZATION AND MODELING OF VANADIUM-CONTAINING POLYOXOMETALATE CATALYSTS

The catalyzed oxidative dehydrogenation of isobutyric acid by H-4[PMo1 1VO40] and VOH[PMo12O40] was studied at 593 K. Thermal evolution of H- 4[PMo11VO40] at 593 K leads to a complex mixture of different species with or without vanadium inside the Keggin structure. After reaction, the one and only heteropolyanion is partly reduced [PMo12O40](3-) and vanadium is present as vanadyl cations. Vanadyl cations are bound to t he oxygen atoms of the heteropolyanion at 593 K and enhance the select ivity to methacrylic acid with respect to acetone. On the other hand, copper cations improve the reoxidation of the catalyst and increase th e IBA conversion. Synergism between copper and vanadyl cations was obs erved.