Structural Characteristics of Alumina-supported Activated Hydrodesulfurization Catalysts - An Xps, No Adsorption and Sulfhydryl-group Study

In the present work we analysed the surface properties of alumina-supported Co-Mo hydrodesulfurization catalysts, submitted to five different activation procedures. We measured the dispersion of the active elements (by XPS), the coordinative unsaturation state (infrared study of NO adsorption) and the sulfhydryl group (chemical titration with AgNO3) concentration. The results confirmed the deep influence of the activation conditions on the parameters analysed. We also showed that hydrogen sulfide tended to adsorb on the coordinatively unsaturated sites (CUS). The structure of the catalysts was shown to change, from the monometallic samples to the bimetallic, leading to a behaviour different from that of its individual components. Namely, the NO adsorption capability, the SH concentration and, sometimes, the surface sulfur concentration, decreased. The results obtained allowed us to speculate that one of the roles of cobalt, in CoMo catalysts, would be that of improving the efficiency of surface sulfur removal.