Hydrodesulfurization properties of rhodium phosphide: Comparison with rhodium metal and sulfide catalysts

Silica-supported rhodium phosphide (Rh2P/SiO2) catalysts were prepared and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), 31P solid-state NMR spectroscopy, X-ray photoelectron spectroscopy (XPS), and chemisorption measurements. XRD and TEM analysis of a 5 wt.% Rh2P/SiO2 catalyst confirmed the presence of well-dispersed Rh2P crystallites on the silica support having an average crystallite size of 10 nm. NMR spectroscopy showed unsupported and silica-supported Rh2P to be metallic and XPS spectroscopy yielded a surface composition of Rh1.94P1.00 that is similar to that expected from the bulk stoichiometry. The 5 wt.% Rh2P/SiO2 catalyst exhibited a higher dibenzothiophene (DBT) hydrodesulfurization (HDS) activity than did Rh/SiO2 and sulfided Rh/SiO2 catalysts having a similar Rh loading and was also more active than a commercial Nisingle bondMo/Al2O3 catalyst. The Rh2P/SiO2 catalyst showed excellent stability over a 100 h DBT HDS activity measurement and was more S tolerant than the Rh/SiO2 catalyst. The Rh2P/SiO2 catalyst strongly favored the hydrogenation pathway for DBT HDS, while the Rh/SiO2 and sulfided Rh/SiO2 catalysts favored the direct desulfurization pathway.