XANES/EXAFS study and catalytic properties of the confined Cr carbonyl-MCM41 system.

F. G. REQUEJO; J. M. RAMALLO-LÓPEZ; R. ROSAS-SALAS; J. M. DOMÍNGUEZ; J. A. RODRIGUEZ; J-Y. KIM; R. QUIJADA

CATALYSIS TODAY

Año: 2005 vol. 107 p. 750 - 758

0920-5861

X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) were performed to determine the structural stability and atomic local order of transition metal carbonyls Cr(CO)6 confined into the channel network of MCM-41. These species interact with the surface siloxane groups of the MCM-41 walls as proved by XANES/EXAFS. These Cr species were previously characterized by FT-IR, Xe adsorption and 29Si NMR, which confirmed their monodispersity, chemical interaction and confinement into thepore network of MCM-41. In this study, XAS provides additional evidence on the high dispersion of the metal species and symmetry of the Cr sites. Also, the Cr–O bond lengths, Cr coordination and oxidation state were determined after thermal treatments, thus confirming theinteraction of the sub-carbonyl species with the siloxane groups. The change of the oxidation state from 0 to almost 3 might explain the unusual catalytic activity for ethylene polymerization of the Cr sub-carbonyl species confined into MCM-41.