Structural characterization and catalytic performance of alkali (K) and metal (Co and Rh)-promoted MoS2 catalysts for higher alcohols synthesis

A series of alkali and metal (Rh and Co) promoted MoS2 catalysts were prepared for the higher alcohols synthesis reaction. The effects of alkali and metal promoters on the performance and structure of molybdenum-sulfided catalysts were studied using the BET, X-ray diffraction (XRD), and X-ray absorption near edge structure (XANES) at the S K-edge and Mo L-3-edge. Alkali (K) promotion to trimetallic (Co-Rh-Mo) catalyst supported on multi-walled carbon nanotubes (MWCNTs) showed less CO conversion compared to that of the catalyst without K. The promotion of alkali reduces the hydrogenation ability of alkyl species to form alkanes and increases the active sites for the formation of alcohols, which is consistent with the observation of higher surface area and larger pore diameters in the K-promoted catalysts. XRD patterns showed that alkali-promoted catalysts were less crystalline compared to that of the catalyst not promoted with K. More oxidized S and Mo species were observed by XRD and XANES in the K-promoted catalysts, indicating the formation of more Mo oxide with the addition of K. thus increasing the active sites. The alkali-promoted trimetallic catalysts using two different supports, MWCNTs and active carbon (AC), showed very different catalytic performances. The activity of the AC-supported alkali-promoted trimetallic catalyst was lower than that supported on MWCNTs. More intense features corresponding to the oxidized S and Mo species were observed in both S K-edge and Mo L-3-edge spectra of the MWCNT-supported catalysts. Finally, formation of Co (Rh)-Mo-S species was evident in the XANES spectra of bimetallic and trimetallic alkali-promoted MoS2 catalysts, in agreement with their improved catalytic performance. (C) 2010 Elsevier B.V. All rights reserved.