Highly Active Silica-supported Rhodium Phosphide Hydrodesulfurization Catalyst Prepared by Sequential Impregnation to Control the Rhodium and Phosphorus State

The effects of the preparation method on Rh and P species in P-added Rh catalysts, as well as hydrodesulfurization (HDS) activities, were investigated. Ultraviolet-visible diffuse reflectance spectroscopy, temperature-programmed reduction, X-ray diffraction (XRD), and CO adsorption analyses were used to characterize the catalysts. Rh species were highly dispersed in the Rh/P/SiO2 catalyst prepared by sequential impregnation. Phosphate interacting with the SiO2 surface will react with Rh complex to form Rh–phosphate complex, so highly dispersed rhodium phosphate species were present on the SiO2 support in the catalyst. Phosphates supported on SiO2 and highly dispersed Rh2O3 particles were impregnated sequentially in the P/Rh/SiO2 catalyst, resulting in Rh species covered with P on the SiO2 support. Polynuclear Rh complexes were formed in the Rh–P/SiO2 catalyst. Dispersion of Rh species by XRD patterns and CO uptakes was in the order Rh/P/SiO2 > P/Rh/SiO2 ≈ Rh–P/SiO2. HDS activities were in the order Rh/P/SiO2 > P/Rh/SiO2 ≈ Rh–P/SiO2. High HDS activity of the Rh/P/SiO2 catalyst depends on Rh2P dispersion with very many exposed Rh sites.