Effects of starting cobalt salt upon the cobalt-alumina interactions and hydrodesulfurization activity of CoO/Al 2O 3

Abstract

The effects of the starting cobalt salt were investigated on the cobalt—alumina interaction modes and cobalt dispersion in CoO/Al 2O 3, catalysts. The catalysts were characterized in oxidic, sulfided, and uncalcined states using temperature-programmed reduction, X-ray photoelectron spectroscopy, X-ray diffraction, and nitric oxide adsorption techniques. It was found that the cobalt—alumina interaction modes depend strongly on the starting salt. It was demonstrated that CoO/Al 2O 3 catalysts prepared from cobalt acetate show higher cobalt dispersion and higher catalytic activity for thiophene hydrodesulfurization than the catalysts prepared from conventional cobalt nitrate. The proportion of Co 3+ species on CoO/Al 2O 3 is significantly decreased when cobalt acetate is used instead of cobalt nitrate. On the basis of XPS characterization of uncalcined catalysts and a comparative study on CoO/Al 2O 3 catalysts prepared from other cobalt precursors, it is proposed that with CoO/Al 2O 3, prepared from cobalt nitrate, the oxidation of Co 2+ to Co 3+ during calcination by coexisting NO − 3 anions on uncalcined precursors results in a high Co 3+ proportion and, consequently, poorly dispersed cobalt species.