Hydrodesulfurization over model sulfide cluster-derived catalysts

Abstract

There is growing interest in the use of organometallic clusters as precursors to model heterogeneous catalysts. This interest is partially derived from the expectation that "solid-state metal complex catalysts" will be uniform in composition and structure thus more amenable to characterization than catalysts prepared using conventional techniques. This research used a series of sulfide clusters as precursors to model heterogeneous catalysts in an effort to enhance our understanding of the active sites in hydro-desulfurization catalysts. Alumina supported catalysts derived from the sulfide clusters Cp2Mo2([mu]-SH)2([mu]-S)2, Cp2Mo2Co2([mu]3-S)2([mu]4-S)(CO)4, and Cp2Mo2Fe2([mu]3-S)2(CO)8 (Cp=cyclopentadienyl) shared important catalytic and spectroscopic features with a commercial catalyst and unsupported MoS2. These strong similarities implied that the active sites in the sulfide cluster-derived catalysts could be used as models of the sites in conventionally prepared hydrodesulfurization catalysts. The active sites in the bimetallic sulfide cluster-derived catalysts appeared to be highly dispersed ensembles containing Mo[delta]+ ([delta]2 and C3 hydrocarbons while the commercial catalyst produced mostly C4 hydrocarbons. These results suggested that C-C bond hydrogenolysis preceded C-S bond cleavage over the sulfide cluster-derived catalysts. More subtle differences between the product distributions of the cluster-derived catalysts have been attributed to differences in the nature of sulfide ligands in their precursors.