Characterization of highly dispersed cobalt sulfide catalysts by X-ray absorption fine structure and magnetic properties

Abstract

Zeolite-supported cobalt sulfide catalysts, CoS/NaY and CoS/USY-H, were prepared using Co(CO) 3NO as a precursor. A SiO 2-supported cobalt sulfide catalyst was prepared by an impregnation method for comparison. The prepared catalysts were characterized by magnetic properties and XAFS. The cobalt sulfides in CoS/NaY are paramagnetic and can be characterized as intrazeolite dinuclear species with antiferromagnetic interactions between the Co atoms, in contrast to the cobalt sulfides in CoS/SiO 2, in which 95% of Co is Co 9S 8 and 5% is paramagnetic with a very small amount of ferromagnetic species. The structure of the cobalt sulfides in CoS/USY-H depends on the treatment after the sulfidation. Ultra-highly dispersed cobalt sulfide species initially formed during the sulfidation are transformed to highly dispersed Co 9S 8-like particles and eventually to ion-exchanged Co 2+ cations as the evacuation temperature and duration are increased. The catalytic activity of the cobalt sulfide catalysts was measured for the hydrodesulfurization of thiophene. The results suggest a synergy generation between cobalt sulfides and surface hydroxyl groups.