Structural Characterization of Rhodium-Containing Hydrodesulfurization (HDS) Catalysts Derived from a Laser Vaporization Cluster Source

Abstract

A series of highly dispersed Rh-based materials have been prepared by deposition of laser-generated gas-phase clusters onto an industrial-grade alumina. While the diameter of the gas-phase metal clusters could be kept at or below 1 nm, the average diameter of the resulting supported Rh particles was always at least 1.5 nm. The reaction of the clusters with either O2or C2H4failed to prevent Rh aggregation on the alumina surface. The addition of O2upstream of the Rh target was sufficient to form bulk Rh2O3, whereas downstream addition of O2or C2H4to the Rh clusters was insufficient to form Rh oxide particles. Most of the Rh-containing particles further aggregated during either sulfiding or HDS testing. Nevertheless, the resulting rhodium sulfides were comparable in activity to sulfided, commercial Co–Mo or Ni–Mo catalysts on a per gram of catalyst basis and superior on a per gram of metal basis. At low loadings (0.1 wt%), the cluster-derived catalysts were more hydrogen-efficient than the commercial catalysts.