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

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, H2 or H2/H2S) at different pressures, then by thiophene hydrodesulfurization (HDS) catalytic activity test at atmospheric pressure. The presence of sulfur (presulfidation by H2S) was not required to convert the model compounds into active catalysts, a beneficial influence of H2S on the activity was only to facilitate the reduction process into the most active Ni2P or less active Co2P phases. Ni(P)/SiO2 catalysts were also prepared, characterized and tested in thiophene HDS. For sulfided P-free Ni/SiO2 catalysts the HDS activity correlated with the Ni3S2 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 Ni2P (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 Ni2P or Co2P present in the material.