Characterization of a Fischer-Tropsch catalyst prepared by decarbonylation of dodecacarbonyltetracobalt on alumina

Abstract

When supported on partially dehydroxylated ..gamma..-Al/sub 2/O/sub 3/, Co/sub 4/(CO)/sub 12/ is an active Fischer-Tropsch (F-T) catalyst. The catalyst is deposited out of hexane solution, thermally decarbonylated, and reacted in the presence of 3:2 H/sub 2/-CO at 250/sup 0/C. The zerovalent cluster, when initially deposited on the support, is extremely sensitive to oxidation. X-ray photoelectron spectroscopy(XPS) indicates that the extent of oxidation is to Co (2). XPS of the decarbonylated and used catalyst indicates the presence of reduced cobalt species in addition to Co(2). This latter observation is supported by laser-induced mass spectroscopy (LIMS). After thermal decarbonylation, the LIMS shows that cobalt clusters, CO/sub x/(x=2,5,6,7), are present. After one F-T cycle, only Co/sub 4/ clusters of the type Co/sub 4/(CO)/sub x/ (x=2-6) and cluster carbides, Co/sub 4/(CO)/sub x/C(x=0,1,2,4,11), are present on the surface. Under mild conditions, the catalyst after one F-T cycle cannot be completely reduced to Co(0) nor oxidized to Co(3) as evidenced by the XPS of H/sub 2/- and 0/sub 2/-treated samples. Transmission electron microscopy (TEM) showed no visible Co particles (>10nm) on any sample. 4 figures, 4 tables.