Abstract
For the purpose of uncovering the cause of increased hydrodesulfurization (HDS) activity of Co-Mo/Al2O3 by the addition of nitrilotriacetic acid (NTA), the effects of order in adding NTA and the amount thereof on benzothiophene (BT) HDS activity were investigated. Effects of pretreatment condition were also studied, and it appeared that NTA did not affect the optimum pretreatment condition. From the view of the surface structure, XPS was measured for the catalyst precursors, Mo EXAFS, FT-IR of adsorbed nitric oxide (NO), and the amount of NO adsorbed were measured for the sulfided catalysts, respectively. The XP spectra showed some concentration of Co at the surface of the catalyst precursor prepared with NTA. From the result of Mo EXAFS, it was thought that, when NTA was added during preparation, the growth of MoS2-like crystallite or the extent of crystallization was promoted. The IR spectra of NO adsorbed on sulfided catalysts showed that the adsorbed NO was mainly located on Co site. It was hence suggested that the addition of NTA promoted the coverage of Mo site with Co, and that the Co might have contributed toward the high HDS activity. The amount of NO adsorbed was found smaller for NTA-added catalyst than for the one prepared without NTA. Since the BT HDS activity was higher for NTA-added catalyst, it was thought that the addition of NTA might have promoted the formation of highly active sites.
