Insight for the effect of bridging [formula omitted] in molybdenum sulfide catalysts toward sulfur-resistant methanation

Abstract

Unsupported MoS2 catalysts were synthesized by a one-step hydrothermal method using ammonium heptamolybdate and thiourea at different temperatures ranging from 150 °C to 180 °C. With the decrease of hydrothermal temperature, the obtained MoS2 catalyst showed an increased sulfur-resistant methanation performance. The physical structure and chemical characteristics of the catalysts were analyzed by N2-physisorption, XRD, SEM, HRTEM, Elemental Analyzer, H2-TPR, XPS and Raman techniques. Combining the catalytic performance trend with the characterization analysis results, we found that the catalysts obtained at lower temperature contain more bridging S22- groups, that is beneficial for H2 dissociation and methanation reaction. We deduced that over-stoichiometric sulfur in the catalyst existed in the form of bridging S22- groups, which increased with the decrease of hydrothermal temperature. The finding that the positive role of the bridging S22- groups rather than the S vacancies in MoS2 catalyst is helpful for designing high efficient MoS2 catalysts not only for methanation but also for other hydrogenation reactions.