Phosphorus promotion of Ni (Co)-containing Mo-free catalysts in thiophene hydrodesulfurization

Abstract

Several unsupported nickel (cobalt)–phosphorus (sulfur) model compounds were prepared, identified and characterized by X-ray diffraction (XRD), electron microscope (EM)/energy dispersive X-ray analysis (EDAX), temperature programmed sulfidation (TPS), BET, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). They were characterized again following pretreatments (in He, H 2 or H 2/H 2S) at different pressures, then by thiophene hydrodesulfurization (HDS) catalytic activity test at atmospheric pressure. The presence of sulfur (presulfidation by H 2S) was not required to convert the model compounds into active catalysts, a beneficial influence of H 2S on the activity was only to facilitate the reduction process into the most active Ni 2P or less active Co 2P phases. Ni(P)/SiO 2 catalysts were also prepared, characterized and tested in thiophene HDS. For sulfided P-free Ni/SiO 2 catalysts the HDS activity correlated with the Ni 3S 2 surface area determined by dynamic oxygen chemisorption (DOC). The addition of phosphorus causes a strong increase in HDS activity of silica supported catalysts, which are much higher than could be expected by their nickel sulfide surface area, therefore, the formation of Ni 2P (identified by XRD) again explains their high activity. The HDS activity of phosphorus promoted nickel (or cobalt) containing molybdenum-free catalysts is related to the amount and dispersion of Ni 2P or Co 2P present in the material.