Laser Raman spectroscopy (LRS) and time differential perturbed angular correlation (TDPAC) study of surface species on Mo/SiO2 and Mo,Na/SiO2. Their role in the partial oxidation of methane

A.J. MARCHI; E.J. LEDE; F.G. REQUEJO; M. RENTERÍA; S. IRUSTA; E.A. LOMBARDO; E.E. MIRÓ

CATALYSIS LETTERS

SPRINGER

Lugar: Berlin; Año: 1997

1011-372X

Silica-supportedmolybdenum(1.6 and 5.0 wt%) andmolybdenum(5 wt%)^sodium(0.4 wt%) catalysts have been characterized by laser Raman spectroscopy (LRS), time differential perturbed angular correlation (TDPAC), temperature-programmed reduc-tion (TPR) and X-ray photoelectron spectroscopy (XPS). The presence of different molybdenum species was correlated with activity and selectivity to formaldehyde during themethane partial oxidation reaction. The main species identified on theMo(5.0 wt%) /SiO2 surface were MoO3 and monomeric species with a single MoˆO terminal bond. The pre-impregnation of the silica support with sodium strongly diminishes the MoˆO concentration due to the formation of Na2Mo2O7 species and tetrahedral monomers with a high degree of symmetry. As a result of these modifications, both methane conversion and formaldehyde formation are strongly inhibited. The combination of LRS and TDPAC techniques resulted in a powerful tool for the identification and quantification of themolybdenumspecies present on the surface of a silica support.