Presulfidation and activation mechanism of Mo/Al2O3 catalyst sulfided by ammonium thiosulfate

Mo/Al₂O₃ catalyst was presulfided with (NH₄)₂S₂O₃ to elucidate presulfidation and activation mechanism. It is illustrated that the Mo oxide is firstly partially sulfided during presulfidation and then in situ reduced into MoS_2?x in activation, and finally sulfided to active state during hydrodesulfurization (HDS). A synergistic effect between the S^2? and S⁶⁺ ions in (NH₄)₂S₂O₃ produces a positive influence on the HDS performance. The S^2? ions contribute to the sulfidation of Mo ions, while the S⁶⁺ species interact with Al₂O₃ support, weakening the interaction of active species with support.