Abstract: Ammonium thiosulfate ((NH₄)₂S₂O₃) was used as a sulfiding agent for presulfiding CoMo and NiMoP catalysts. The effect of the amount of (NH₄)₂S₂O₃ on hydrodesulfurization (HDS) activity was investigated. For the CoMo series, the use of a proper amount of (NH₄)₂S₂O₃ gave a higher HDS activity than when the catalyst was sulfided by H₂S. SO₄^2– formed during presulfidation modified the Al₂O₃ support and decreased the interaction between the active phase and support, and the activity was enhanced. However, a smaller amount of (NH₄)₂S₂O₃ used for the presulfidation would result in insufficient sulfidation, while a larger amount of (NH₄)₂S₂O₃ increased the particle size of the active phases, and both were harmful to HDS activity. For the NiMoP series, the presulfided catalysts were less active than those sulfided by H₂S. This was ascribed to the high metal content and the addition of P to the catalyst.

Key words: hydrodesufurization, presulfidation, ammonium thiosulfate, thiophene