The Structure And Surface Species Of K-Co-Mo/C Catalysts And In Situ DRIFTS Study Of Higher Alcohols Synthesis Reaction

Increasing concerns on the global climate change, depletion of fossil fuel resources and the high price of the oil have promoted the rapid development of biofuels market. Higher alcohols can not only substitute for the MTBE (methyl tert-buthyl ether) and be added into the gasoline improving the octane enhancer but also be an important clean fuel for producing only CO2and H2O when it is combusted. Of the several catalytic systems studied for higher alcohols synthesis, molybdenum-based catalysts are of considerable interest because of excellent resistance to sulfur and mild reaction condition. In this paper, a series of K-Co-Mo/C catalysts were synthesized using sol-gel method and characterized by the means of XRD, H2-TPR, XPS and in situ DRIFTS to study the structure, valence state, active sites and the reaction of higher alcohols from syngas. The results we obtained are listed below.(1) The effects of molar ratios of Co/Mo on the catalyst structure were investigated. For the fresh catalysts, Mo species were mainly Mo6+and Mo4+. The addition of small amount of Co promoted the dispersion of the catalyst and reduced the particle size. The CoMoO3phase appeared when the the extra amount of Co was added. For the reduced catalysts, the crystallinity of the catalysts significantly increased. The moderate amount of Co facilitated the reduction of MoO2and formed a new species of Moδ+. The percentage of Moδ+was maximum when the molar ratio of Co/Mo was0.5.(2) The effects of reduction temperatures of the catalyst with Co/Mo=0.5on the catalyst structure were investigated. There were more MoO2when the reduction temperature increased from673K to773K. However, the phase of Mo3Co3C appeared when the reduction temperature increased to873K which was because too high reduction temperature caused the sintering of the catalyst. The percentage of Moδ+was the maximum and up to48.66%when the reduction temperature was773K. In addition, the Co species went into the bulk phase from surface with the increasing reduction temperature.(3) The effects of the molar ratios of Co/Mo and reduction temperatures on the syngas absorption were investigated. The addition of Co can enhance absorption strength of syngas on the catalysts surface. The adsorption on Moδ+was maximum when the molar ratio was0.5and the reduction temperature was773K. With the data of catalytic performance, it was believed that the Moδ+was the active site for higher alcohols synthesis.(4) The reaction of higher alcohols synthesis from syngas of the catalyst with Co/Mo=0.5was studied. The results showed that the major products were methane, methanol, light alkane and higher alcohols.