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 Moexchanged sites in zeolites.

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A study of the stability, local order, and interaction of the surface silanol groups of MCM-41 with transition metal carbonyls M x (CO) y (where M = Cr, Mn, Fe, Co) introduced by a chemical alternative method was performed by X-ray absorption near-edge spectroscopy (XANES). These molecular species, catalytically active for ethylene polymerization reactions, were previously characterized by FTIR and NMR in order to confirm their monodispersion and confined location into the mesopores of the MCM-41 material. Present experimental results indicate the high dispersion of metal species in all cases. Symmetry and stability depend on type of compound, Fe-carbonyl having the lowest stability. Changes in metal coordination and oxidation state are clearly followed by XANES indicating the interaction between sub-carbonyl species and the walls of the mesopores.