| There is currently a great deal of interest in the use of cluster derived catalysts. Unfortunately, most polynuclear clusters decompose following contact with the support or during pretreatment, and their resulting structure and catalytic behavior closely resemble those of a conventionally prepared catalyst.; The objective of this work was to rationally design an active and sulfur tolerant Fischer-Tropsch synthesis catalyst. In this study, a novel class of polynuclear cluster catalysts was investigated. The bimetallic sulfide clusters, Cp(,2)Mo(,2)Fe(,2)S(,2)(CO)(,8) and Cp(,2)Mo(,2)Co(,2)S(,3)(CO)(,4) were synthesized and anchored onto (gamma)-Al(,2)O(,3) supports. The presence of strong metal-metal bonds and bridging sulfide ligands provide structural stability to the cluster. The composition of these clusters made them candidates for hydrodesulfurization.; These catalysts were characterized before and after exposure to reaction conditions by Mossbauer spectroscopy, infrared spectroscopy, and electron microscopy. In addition, in situ Mossbauer spectroscopy allowed direct observation of the chemistry of the working catalyst. The results suggest that the cluster derived catalytic ensembles remain essentially unchanged during, and after exposure to Fischer-Tropsch synthesis and hydrodesulfurization (HDS) conditions. Whether or not these ensembles are structurally related to the precursor clusters remains the subject of further research. Nevertheless, these structurally stable ensembles appear to be models of the active HDS site. This is a major accomplishment in that the exact nature of the active HDS site has not been determined despite very intensive study.; These cluster derived catalysts allow excellent control over the composition of the active sites, and consequently the promoter effect is accomplished with very low loadings. Furthermore, their ability to cleave C-C bonds without concomitant hydrogenation of olefinic bonds is unprecedented. The development of a catalyst which can remove sulfur and simultaneously produce smaller unsaturated hydrocarbon fragments has obvious economical advantages. |
