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In this work, we have investigated the activation process and structure of Ni-promoted Mo x W(1–x)S2/Al2O3 hydrodesulfurization (HDS) catalysts. Conversion of Mo and W oxides to the catalytically active MS2 (M = Mo, W) phase by sulfidation in gaseous H2S/H2 proceeded via different pathways, as found by XPS and EXAFS. The slower sulfidation kinetics of W on the alumina support formed NiMo x W(1–x) sulfides with a two-dimensional core–shell structure. Mo was mostly located in the core and W in the shell, as evidenced by EXAFS. Increasing the H2S/H2 pressure during sulfidation distributed Mo and W more homogeneously in the metal sulfide particles. This was attributed to the more favorable sulfidation of W under these conditions (i.e., below the temperature of MoS2 formation). Catalytic testing was consistent with these findings and demonstrated that a core–shell structure is the active phase in thiophene HDS (1 atm), whereas a homogeneously mixed MS2 phase catalyzes the HDS of dibenzothiophene at 40 bar. This is the first example of a core–shell structure in promoted Mo x W(1–x)S2 catalysts. Support interactions in the oxidic precursor, which affect the sulfidation kinetics, were determined to play a key role in the formation of these structures.

K-promoted MoS 2 is an active catalyst for the synthesis of CH 3 SH, a valuable chemical intermediate, from synthesis gas (CO/H 2 ) and H 2 S. The promotion of MoS 2 by K increases the CO conversion rate and the CH 3 SH selectivity and is usually linked to the stabilization of the 1T-MoS 2 polymorph as compared to the 2H-MoS 2 in K-free samples. Sulfided catalysts were characterized using TEM, XPS, and EXAFS. TEM showed that MoS 2 particles became larger and more stacked when the K/Mo ratio increased above unity. XPS and EXAFS evidenced the formation of the 1T-MoS 2 phase at higher K/Mo ratio in addition to 2H-MoS 2 . The addition of K to MoS 2 led to increased CH 3 SH productivity due to both increased CO conversion and CH 3 SH 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-MoS 2 phase slowly converted to the 2H-MoS 2 phase during the reaction at high pressure. There is no correlation between the CH 3 SH productivity and the amount of 1T-MoS 2 in K-promoted MoS 2 catalysts.

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