Effect of Mg/Al molar ratio on the COS hydrogenation performance of MoS_x/MgO-Al₂O₃ catalyst

MgO-Al₂O₃ supports with Mg/Al molar ratio of 0, 0.2, 0.5 and 1.0 were synthesized by coprecipitation method. Mo/M-A₀-S, Mo/M-A_0.2-S, Mo/M-A_0.5-S, and Mo/M-A_1.0-S catalysts were respectively prepared by molybdenum loading and followed by prevulcanization processes. Their catalytic performances for hydrogenation of COS in coke oven gas were evaluated in a fixed bed reactor. X-ray photoelectron spectroscopy and Raman spectroscopy were used to characterize the structure and Mo species of catalysts, and the effect of Mg/Al molar ratio on the COS hydrogenation performance of catalyst was investigated. The results show that the changing of Mg/Al molar ratio can modify the physical and chemical structure of MgO-Al₂O₃ support, the dispersion of Mo and its interaction with catalyst support, and the amount and layer number of MoS₂ active sites, so that to improve the activity and selectivity of catalyst. The Mg/Al molar ratio 0.5, which is equal to the stoichiometric ratio of Mg to Al in MgAl₂O₄, is the most favorite value for MgAl₂O₄ production. MgAl₂O₄ can reduce the interaction strength between Mo and catalyst support, enhance Mo dispersion, increase MoS₂ amount, and thus promote the catalyst performances. Mo/M-A_0.5-S is an excellent catalyst, which can convert 97.7% COS through hydrogenation with H₂S selectivity 100% in 550 min at 280 ℃ under the space velocity of 62000 h⁻¹.