Investigation of the reaction pathway for synthesizing methyl mercaptan (CH(3)SH) from H(2)S-containing syngas over K–Mo-type materials

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.