XANES Mo L-edges and XPS study of mo loaded in HY zeolite

Molybdena-containing ultrastable (HY) zeolites, prepared using several Mo precursors and activation procedures, were characterized by X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopy (XPS). Combined XANES Mo L-edge and XPS results revealed that the Mo 4d electronic level is not strongly influenced by the preparation procedures but that it is clearly modified by the presence of Pd. The splitting of 2.4-2.6 eV obtained in the white line at both Mo L-II,(III)-edges clearly indicated that Mo was tetrahedrally coordinated in all dehydrated catalysts. The Mo oxidation state, evaluated by the energy shift in the absorption edge, was also independent of the synthesis process. The Mo L-II-edge is discussed for the first time as a very sensitive probe to determine the nature of Mo species. Even the XANES L-III-edge relative intensity of the maximum at the split white line depends on the Mo coordination; at the L-II-edge, intensities do not depend on Mo coordination alone. This aspect should be associated, consistent with the binding energy (BE) of 3d levels observed by XPS, with the presence of Al atoms at the second Mo-surrounding in Mo-exchanged sites in zeolites.