The synthesis of methanethiol from CS2 catalyzed by Ni-, Co-, or K-modified MoS2/SiO2 through the sequence CS2→CH3SH→CH3SCH3 (DMS) has been studied. CS2 is readily hydrogenated to CH3SH, whereas CH3SH and DMS decompose to CH4 at high CS2 conversions and temperatures. Thus, very high yields of CH3SH can be obtained on all the catalysts. The addition of Co or Ni accelerates all reaction steps to allow the formation of CH3SH under relatively mild conditions. On the contrary, K suppresses the formation of byproducts but also lowers the activity. The surface reaction proceeds through a series of hydrogen-addition steps, the rate-controlling step of which is the addition of the first H atom. H2 adsorbs dissociatively, whereas CS2 adsorbs strongly in a single active site prior to hydrogenation. The addition of Ni has a stronger enhancing effect on hydrogenation and accelerates the CS bond cleavage to a smaller extent than Co. Therefore, Ni leads to optimum CH3SH yields and holds the best promise as promoter for the MoS2 phase in the synthesis of methanethiol from CS2.
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