EPR OF VANADIUM IN CE0.25H3PVMO11O40 CATALYST - FORMATION OF VANADYL DIMERS DURING THE OXIDATIVE DEHYDROGENATION OF ISOBUTYRIC ACID

The catalytic oxidative dehydrogenation of isobutyric acid (IBA) to me thacrylic acid (MAA) over the heteropolyacid Ce0.25H3PVMo11O40 has bee n studied. After catalysis, the vanadium ions are ejected from the Keg gin structure as vanadyl dimers. Such species remain stable at room te mperature in the presence of water. The presence of cerium as a counte r-cation appears to promote dimer formation. The distance between the two VO2+ ions in the dimer has been estimated to be 4.31 Angstrom. The dimers are located on oxygen vacancies near Ce4+ ions. The hyperfine structure of the half magnetic field signal obtained was well resolved . 15 lines with relative intensities: 1, 2, 3, 4, 5, 6, 7, 8, 7, 6, 5, 4, 3, 2, 1 have been observed.