THE SOLID-STATE REARRANGEMENT OF THE WELLS-DAWSON K6P2W18O62-CENTER-DOT-10H(2)O TO A STABLE KEGGIN-TYPE HETEROPOLYANION PHASE - A CATALYST FOR THE SELECTIVE OXIDATION OF ISOBUTANE TO ISOBUTENE

The thermal and structural stability of the Wells-Dawson-type heteropo ly compound K6P2W18O62. 10H(2)O was examined by FT-IR spectroscopy, X- ray powder diffraction, thermogravimetric analysis and HRTEM. It was f ound that calcination at temperatures higher than 850 K led to the for mation of a Keggin-type compound ''K3PW12O40'', containing small amoun ts of an additional phase originated from the high-temperature interac tion between potassium phosphate (K3PO4, formed during the decompositi on of the K6P2W18O62. 10H(2)O) and the Keggin-type compound itself. Th e Keggin-type product showed a higher activity in the selective oxidat ive dehydrogenation of isobutane to isobutene compared to both the Wel ls-Dawson precursor and to pure, authentic K3PW12O40. This higher acti vity can be tentatively attributed to the presence of an amorphous lay er of unknown stoichiometry at the surface of the thermally rearranged Wells-Dawson compound.