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.