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The cooperative transition of sulfur-containing pollutants of H2S/CO/H2 to the high-value chemical methyl mercaptan (CH3SH) is catalyzed by Mo-based catalysts and has good application prospects. Herein, a series of Al2O3-supported molybdenum carbide catalysts with K doping (denoted herein as K-Mo2C/Al2O3) are fabricated by the impregnation method, with the carbonization process occurring under different atmospheres and different temperatures between 400 and 600 °C. The CH4-K-Mo2C/Al2O3 catalyst carbonized by CH4/H2 at 500 °C displays unprecedented performance in the synthesis of CH3SH from CO/H2S/H2, with 66.1% selectivity and a 0.2990 g·gcat−1·h−1 formation rate of CH3SH at 325 °C. H2 temperature-programmed reduction, temperature-programmed desorption, X-ray diffraction and Raman and BET analyses reveal that the CH4-K-Mo2C/Al2O3 catalyst contains more Mo coordinatively unsaturated surface sites that are responsible for promoting the adsorption of reactants and the desorption of intermediate products, thereby improving the selectivity towards and production of CH3SH. This study systematically investigates the effects of catalyst carbonization and passivation conditions on catalyst activity, conclusively demonstrating that Mo2C-based catalyst systems can be highly selective for producing CH3SH from CO/H2S/H2. [ABSTRACT FROM AUTHOR]

The reaction pathway for synthesizing methyl mercaptan (CH 3 SH) using H 2 S-containing syngas (CO/H 2 S/H 2 ) as the reactant gas over SBA-15 supported K-Mo-based catalysts prepared by different impregnation sequences was investigated. The issue of the route to produce CH 3 SH from CO/H 2 S/H 2 has been debated for a long time. In light of designed kinetic experiments together with thermodynamics analyses, the corresponding reaction pathways in synthesizing CH 3 SH over K-Mo/SBA-15 were proposed. In the reaction system of CO/H 2 S/H 2 , COS was demonstrated to be generated firstly via the reaction between CO and H 2 S, and then CH 3 SH was formed via two reaction pathways, which were both the hydrogenation of COS and CS 2 . The resulting CH 3 SH was in a state of equilibrium of generation and decomposition. Decomposition of CH 3 SH was found to occur via two reaction pathways; one was that CH 3 SH first transformed into two intermediates, CH 3 SCH 3 and CH 3 SSCH 3 , which were then further decomposed into CH 4 and H 2 S; another was the direct decomposition of CH 3 SH into C, H 2 S and H 2 . Moreover, the catalyst (K-Mo/SBA-15) prepared with co-impregnation exhibits higher catalytic activities than the catalysts (K/Mo/SBA-15 and Mo/K/SBA-15) prepared by the sequence of impregnation. Based on characterization of the oxidized, sulfided and spent catalysts via N 2 adsorption-desorption isotherms, XRD, Raman, XPS and TPR, it was found that two K-containing species, K 2 Mo 2 O 7 and K 2 MoO 4 , were oxide precursors, which were then converted into main K-containing MoS 2 species. The CO conversion was closely related to the amount of edge reactive sulfur species that formed the sulfur vacancies over MoS 2 phases., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)