Study on ex-situ presulfurization technologies with different presulfiding agents for CoMo-based sulfur-tolerant shift catalysts

(NH₄)₂S and Na₂S were selected from several presulfiding agents. Industrial Co-Mo based sulfur-tolerant shift catalysts were ex-situ presulfided with different presulfurization technologies. The crystal structures, surface characteristics and micro appearance were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (HRTEM). (NH₄)₂S and Na₂S as presulfiding agents did not show obvious effects on the crystal structures of the catalysts. Partial O-S exchange of the active components was observed when (NH₄)₂S was used for presulfirization. And when presulfided with Na₂S, the active components still remained oxidation state. As the ex-situ presulfurization temperature increased, the extent of vulcanization was:S-Na₂S > S-(NH₄)₂S > the general in situ pre-vulcanization. When presulfided with (NH₄)₂S or the general in situ pre-vulcanization, the stacking number of MoS₂ layers was mainly two to three. And when presulfided with Na₂S, the stacking number of MoS₂ layers increased obviously, mostly three to five. The activity sequence of the catalysts was S-Na₂S > S-(NH₄)₂S > the general in situ pre-vulcanization when the catalysts were tested in a micro-fixed reactor at temperatures of 285, 350 and 450℃ respectively.