Sulfidation of MoO3/γ-Al2O3 towards a highly efficient catalyst for CH4 reforming with H2S

The process of CH4 reforming with H2S is an efficient approach to H-2 production, which can not only directly convert sour natural gases without separating H2S from CH4 but can also make full use of waste H2S, making it into high value-added products. In the present study, a MoO3/gamma-Al2O3 material was prepared and further applied to the CH4/H2S reforming process after in situ sulfidation treatment under an H2S/N-2 atmosphere at variable sulfidation temperatures (400-800 degrees C) and times (0-7 h). The reaction conversion and the H-2 production rate of sulfided catalysts were examined under the conditions of 800 degrees C and 1 atm with a molar ratio for CH4/H2S of 1.5 : 1 and a gas hourly space velocity (GHSV) of 15 000 h(-1). By combining various characterization techniques, such as X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy, the effects of sulfidation factors on the structure and the catalytic performance of the Mo-based catalyst were studied. The catalytic activity increased at first and then reduced along with increasing the sulfidation temperature and time, implying the existence of optimal sulfidation conditions, which were identified to be around 500 degrees C for 1 h. Both the sulfidation temperature and time have significant influences on the transformation of MoO3 to MoS2 and consequently affect the phase composition, the crystal size, and the texture, as well as the surface Mo valence states of the sulfurized MoO3/gamma-Al2O3 catalysts. A catalyst structural evolution mechanism during sulfidation and the subsequent reaction process were proposed, and it was speculated that two simultaneous MoS2 formation routes, one through the MoO2 phase and the other through the Mo5+OxS phase, were involved. The relationship between the catalyst structure and the catalytic performance was further established, and the edge Mo atoms were assumed to cooperate with the neighboring surface Mo sites to catalyze the reaction together.