Structures and performance of Pd–Mo–K/Al 2 O 3 catalysts used for mixed alcohol synthesis from synthesis gas

Abstract

The structures of the palladium-modified Mo-K/Al 2 O 3 catalyst samples were characterized by the XRD, LRS, and EXAFS techniques and correlated to the catalytic properties of the samples for alcohol synthesis from synthesis gas. It is found that in the oxidic palladium-modified samples a strong interaction of the palladium modifier with the supported K-Mo-O species occurs. This interaction leads to a decrease in the size of the molybdenum species and stabilization of the cationic palladium species on the samples during sulfidation. Upon sulfidation, the sulfided molybdenum species in the palladium-free sample is mainly present as large patches of MoS 2 -like slabs with their basal sulfur planes interacting with the support surface. With the modification of palladium to the samples, the supported MoS 2 -like species becomes highly dispersed as revealed by the decrease in the average size of the sulfided molybdenum species. The interaction of the palladium species with the molybdenum component may cause the basal planes of the MoS 2 -like species to become oriented perpendicular to the support surface due to favorable bonding of the MoS 2 edge planes to the support through Mo-O-Al bonds. In comparison with the sulfided Pd-free sample, the properties of the Pd-modified samples for alcohol synthesis from synthesis gas are much improved, which most probably results from the synergic interaction of the palladium with the molybdenum species that gives rise to the appearance of the active sites.