Co/SiO2 catalysts for selective hydrogenation of crotonaldehyde II:: influence of the Co surface structure on selectivity

The effect of interaction of silica-supported Coo, on catalytic properties of CO/SiO2 catalysts was investigated. The CoOx, precursors supported on silica were obtained by impregnation of the support with cobalt nitrate solution. Cobalt precursors, with different interactions with support, were obtained by changes of impregnation solvent, drying time and temperature; and calcination temperature. The Co surface structure of the catalysts was characterized by diffuse reflectance FTIR spectroscopy (DRIFTS) of adsorbed CO and temperature-programmed desorption of hydrogen (TPD-H-2). The TPD-H-2 and DRIFT of CO spectra indicate the presence of at least four different Co surface sites, labeled alpha, beta, gamma, and sigma. The relative amount of these species varied depending on the degree of CoOx interaction with SiO2 in precursors. For crotonaldehyde (CROALD) hydrogenation in gas phase, selectivity to crotyl alcohol and butanol depended strongly on the beta/(gamma + sigma) ratio. Interestingly, selectivity to butyraldehyde does not depend on beta, gamma, or sigma sites present. (C) 2002 Elsevier Science B.V. All rights reserved.