XPS AND NO ADSORPTION STUDIES ON ALUMINA-SUPPORTED CO-MO CATALYSTS SULFIDED BY DIFFERENT PROCEDURES

In the present work we studied the distribution of the active phase at the surface of the support, by XPS, of four HDS catalysts, each of them sulfided according to five different procedures. The procedures employed were known to yield catalysts with distinct activities and selectivities. The results of the XPS study were refined with data from an IR study on NO adsorbed on the catalysts. The major consequence of the modification of the activation procedure was a change in the dispersion of the active phase rather than the modification of the oxidation states of the active elements. The diameter of the MoS2 crystallites, rather than the number of slabs per crystallite, was most affected. When H2S was employed in the absence of hydrogen, catalysts containing only Mo contained a large excess of surface sulfur, whereas Co-Mo catalysts still presented S/Mo XPS ratios close to the stoichiometric ones. In these activations, the NO adsorption capability of the catalysts depended on whether the H2S treatment was applied before or after the sulfidation with H-2/H2S. (C) 1995 Academic Press, Inc.