Infrared Spectroscopic Characterization of Sulfide Cluster-Derived Ensembles

ABSTRACTThe transition metal sulfide clusters (MeCp)2Mo2(μ-SH)2(μ-S)2, (MeCp)2Mo2Co2(μ3-S)2(μ4-S)(CO)4 [MoCoS], and (MeCp)2Mo2 Fe2 (μ3-S)2(CO)8, (MeCp = methylcyclopentadienyl) were used to prepare γ-Al2O3-supported catalysts. For comparison, a series of supported materials was also prepared using conventional incipient wetness impregnation. Infrared spectroscopy of adsorbed species was used to characterize the sites in the clusterderived and conventionally prepared catalysts. Nitric oxide chemisorbed onto the MoCoS/A catalyst was associated initially only with Co sites and then upon gentle heating shifted to the Mo sites, indicating that Co and Mo were in close proximity. In contrast, NO adsorbed onto both Co and Mo sites in the conventionally prepared materials and desorbed independently from these two types of sites. Infrared spectra of adsorbed thiophene and pyridine were similar for the clusterderived and conventionally prepared catalysts. Thiophene reacted at 100 °C to produce both olefinic species. The most abundant products from thiophene HDS were 1-butene, cis-2-butene, and trans-2-butene. Displacement studies showed that thiophene, pyridine, and NO adsorbed to the same site. The most active sites for HDS and HDN contained both Mo and a late transition metal. The HDN product distributions suggested that Mo was selective for C=N bond cleavage while the late transition metals were more active for C=C hydrogenolysis.