THE ROLE OF CO IN UNSUPPORTED CO-MO SULFIDES IN THE HYDRODESULFURIZATION OF THIOPHENE

Unsupported Co-Mo catalysts were prepared by impregnation Of MoS2, obt ained by thermal decomposition of ammonium tetrathiomolybdate, with a solution of cobalt nitrate in acetone. XRD and HREM showed that the Mo S2 structure of the resulting catalysts remained intact upon addition of Co. The thiophene hydrodesulfurization and the consecutive butene h ydrogenation properties indicated that the Co ions are preferentially situated at the edges of the MoS2 Crystallites below Co/(Co + Mo) = 0. 08 and promote the hydrodesulfurization (HDS) reaction. Further additi on of Co leads to the segregation of Co9S8, which acts as a support fo r highly dispersed Co-promoted MoS2 Crystallites. As a result of this structural effect, the Co-MoS2 crystallites become better accessible a nd the catalytic activity increases again above Co/(Co + Mo) = 0.2. Th e observed increase in activity upon physical mixing of Co-promoted Mo S2 and Co9S8 might also be explained by such a structural effect, rath er.than by a remote-control effect. (C) 1994 Academic Press, Inc.