Working surface science model of CoMoS hydrodesulfurization catalysts

Model catalysts, consisting of a conducting substrate with a thin SiO2 or Al2O3 layer on top of which the active catalytic phase is deposited, were applied to study the sulfidation of Co–Mo catalysts and to test their catalytic behavior in the hydrodesulfurization of thiophene. CoMoS, the highly active cobalt promoted MoS2 in which Co is thought to decorate the edges of MoS2 slabs, can be synthesized by sulfiding nitrilotriacetic acid complexes of cobalt and molybdenum. These complexes are deposited on SiO2/Si(100) and Al2O3/Si(100) model supports by spin coating. X-ray photoelectron spectroscopy measurements on these Co–Mo catalysts provide detailed insight into the mechanism of sulfidation. It appears that Mo is sulfided first and then the Co; this is imperative to form the CoMoS phase. Thiophene hydrodesulfurization studies of CoMoS model catalysts yield activities and product distributions consistent with those obtained from their high surface area counterparts, proving that these models are realistic. They offer, therefore, a great potential for fundamental surface science studies of catalytic phases and of adsorption, desorption, and reactions of gases as well.