XANES Characterization of Extremely Nanosized Metal-Carbonyl Subspecies (Me = Cr, Mn, Fe, and Co) Confined into the Mesopores of MCM-41 Materials

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.