Synthesis, Characterization, and Hydrodesulfurization Properties of Silica-Supported Molybdenum Phosphide Catalysts

Silica-supported molybdenum phosphide (MoP/SiO2) catalysts have been prepared and characterized by X-ray diffraction (XRD), pulsed chemisorption (CO and O2), scanning and transmission electron microscopy (SEM and TEM, respectively), and X-ray photoelectron spectroscopy (XPS). XRD and TEM analysis of MoP/SiO2 catalysts confirmed the presence of MoP crystallites dispersed on the surface of the silica support, while SEM energy dispersive X-ray microanalysis indicated the bulk composition of the supported MoP particles to be 12.7 atom% Mo and 14.1 atom% P. XPS analysis of a passivated 25 wt% MoP/SiO2 catalyst indicated the presence of two kinds of Mo species as well as phosphide and phosphate species at the catalyst surface. Thiophene hydrodesulfurization (HDS) activities were measured for 15 and 25 wt% MoP/SiO2 catalysts, and for a sulfided Mo/SiO2 catalyst with a Mo loading similar to that of the lower loading MoP catalyst. The 15 wt% MoP/SiO2 catalyst, when pretreated only by degassing in flowing He, was nearly four times more active than the sulfided Mo/SiO2 catalyst after 150 h on-stream. Following an initial decline in HDS activity during the first 3 h of measurement, the MoP/SiO2 catalyst displayed an unusual trend of HDS activity that increased monotonically as a function of time on-stream.