ESR CHARACTERIZATION OF CATALYTICALLY ACTIVE V-CENTER SUPPORTED ON ALUMINA-PILLARED, TITANIA-PILLARED, AND ZIRCONIA-PILLARED MONTMORILLONITE CLAYS

Vanadium-doped alumina-, titania-, and zirconia-pillared montmorilloni tes obtained by various preparative procedures have been investigated with the aid of ESR. Analysis of the spectra shows that localization o f vanadium dopant in the pillared clay structure depends on the type o f pillared matrix and on the mode of preparation. In V-doped alumina- and titania-pillared clays the vanadyl ions are bound to the pillars. In zirconia-pillared samples, beside the vanadyl centres bound to the pillars, also species associated with the interlayer surface of clay p lay an important role. In all cases co-pillaring produces species of r elatively stronger in-plane pi covalency than that observed for other members of the respective series, the effect being most pronounced for (V-Ti)-PILC and (V-Zr)-PILC samples. Catalytic experiments with oxida tive dehydrogenation of propane demonstrate superior catalytic propert ies of these centres. This effect is interpreted in terms of the in-pl ane pi covalency facilitating electron transfer between the electron d onor and electron acceptor sites at the catalyst surface.