Structures and performance of Pd-Mo-K/Al2O3 catalysts used for mixed alcohol synthesis from synthesis gas

The structures of the palladium-modified Mo-K/Al2O3 catalyst samples were c haracterized by the XRD, LRS, and EXAFS techniques and correlated to the ca talytic properties of the samples for alcohol synthesis from synthesis gas. It is found that in the oxidic palladium-modified samples a strong interac tion of the palladium modifier with the supported K-Mo-O species occurs. Th is interaction leads to a decrease in the size of the molybdenum species an d stabilization of the cationic palladium species on the samples during sul fidation. Upon sulfidation, the sulfided molybdenum species in the palladiu m-free sample is mainly present as large patches of MoS2-like slabs with th eir basal sulfur planes interacting with the support surface. With the modi fication of palladium to the samples, the supported MoS2-like species becom es 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 MoS2-like specie s to become oriented perpendicular to the support surface due to favorable bonding of the MoS2 edge planes to the support through Mo-O-Al bonds. In co mparison with the sulfided Pd-free sample, the properties of the Pd-modifie d 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 site s.