CHARACTERIZATION OF SURFACE SPECIES ON V SIO2 AND V,NA/SIO2 AND THEIRROLE IN THE PARTIAL OXIDATION OF METHANE TO FORMALDEHYDE/

Silica-supported vanadium (1-8 wt%) and vanadium (5 wt%)-sodium (0.4 w t%) catalysts have been characterized by laser Raman spectroscopy, tem perature-programmed reduction, X-ray photoelectron spectroscopy, NO NH3 rectangular pulses and oxygen chemisorption. The presence of diffe rent vanadium species was correlated with activity and selectivity dur ing the methane partial oxidation reaction. The pre-impregnation of th e silica support with sodium favors vanadium dispersion, but strongly diminishes V=O concentration due to the formation of orthovanadate-lik e compounds. As a result of these modifications, methane conversion is strongly inhibited while formaldehyde decomposition is favored.