Investigation of the active phase in K-promoted MoS₂ catalysts for methanethiol synthesis

K-promoted MoS2 is an active catalyst for the synthesis of CH3SH, a valuable chemical intermediate, from synthesis gas (CO/H2) and H2S. The promotion of MoS2 by K increases the CO conversion rate and the CH3SH selectivity and is usually linked to the stabilization of the 1T-MoS2 polymorph as compared to the 2H-MoS2 in K-free samples. Sulfided catalysts were characterized using TEM, XPS, and EXAFS. TEM showed that MoS2 particles became larger and more stacked when the K/Mo ratio increased above unity. XPS and EXAFS evidenced the formation of the 1T-MoS2 phase at higher K/Mo ratio in addition to 2H-MoS2. The addition of K to MoS2 led to increased CH3SH productivity due to both increased CO conversion and CH3SH selectivity (T = 300-400 °C, P = 10 bar). The performance of the most active catalyst with a K/Mo ratio of 2 was found to be stable, despite the observation that the initially present 1T-MoS2 phase slowly converted to the 2H-MoS2 phase during the reaction at high pressure. There is no correlation between the CH3SH productivity and the amount of 1T-MoS2 in K-promoted MoS2 catalysts.