Characterization of sulfide cluster-derived HDS/HDN catalysts.

摘要

The transition metal sulfide clusters (MeCp){dollar}sb2{lcub}rm M{rcub}{dollar} o{dollar}sb2(mu{dollar}-SH){dollar}sb2mu{dollar}-S){dollar}sb2{dollar} (MoS), (MeCp){dollar}sb2{lcub}rm Mo{rcub}sb2{lcub}rm Co{rcub}sb 2(musb3{dollar} -S){dollar}sb2(musb4{dollar}-S)(CO){dollar}sb4{dollar} (MoCoS), and (MeCp){dollar}sb2{lcub}rm M{rcub}{dollar} o{dollar}sb2{lcub}rm Fe{rcub}sb2(musb3{dollar}-S){dollar}sb2{lcub}rm (CO){rcub}sb8{dollar} (MoFeS), (MeCp = methylcyclopentadienyl) were used to prepare a series of {dollar}gamma{dollar}-A1{dollar}sb2{lcub}rm O{rcub}sb3{dollar}- supported catalysts. Transmission electron microscopy and chemisorption suggested that the cluster-derived ensembles were highly and perhaps molecularly dispersed. For comparison, a series of supported materials was prepared using incipient wetness impregnation. The conventionally prepared catalysts, while highly dispersed, contained layered structures consistent with MoS{dollar}sb2.{dollar}; The HDS and HDN activities and product distributions of the MoCoS/{dollar}gamma{lcub}rm -A1{rcub}sb2{lcub}rm O{rcub}sb3{dollar} and MoS/{dollar}gamma{lcub}rm A1{rcub}sb2{lcub}rm O{rcub}sb3{dollar} catalysts were similar to those of the conventionally prepared sulfided Mo-Co/{dollar}gamma{lcub}rm -A1{rcub}sb2{lcub}rm O{rcub}sb3{dollar} and Mo/{dollar}gamma{lcub}rm -A1{rcub}sb2{lcub}rm O{rcub}sb3{dollar} catalysts, respectively. The HDS and HDN results indicated that the sulfide cluster-derived ensembles could serve as models of the active sites in commercial hydrotreatment catalysts.; Infrared spectroscopy of adsorbed species was used to characterize the sites in the cluster-derived 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; NO desorbed independently from these two types of sites. Infrared spectra of adsorbed thiophene and pyridine were similar for the cluster-derived and conventionally prepared catalysts. Thiophene reacted at 100{dollar}spcirc{dollar}C (373 K) to produce both olefinic species, which is interesting considering that 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.