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Effect of Pt, Ru and Pd Promoters on the Performance of Co/γ-Al_2O_3 Catalysts for Fischer-Tropsch Synthesis

XU Dongyan, LI Wenzhao*, DUAN Hongmin, GE Qingjie, XU Hengyong ( Laboratory of Natural Gas Utilization and Applied Catalysis, Dalian Institute of Chemical physics, The Chinese Academy of Sciences, Dalian 116023, Liaoning , China)  
Noble metals such as Pt, Ru and Pd have been known to improve the reducibility of Co/ γ-Al2O3 catalyst for Fischer-Tropsch synthesis (FTS). However, little is known about their difference in promoting the reduction of cobalt oxi de and their other promoter action to the Co/ γ-Al2O3 catalyst. In this study we investigated the effects of different noble metals on the properties o f the Co/ γ-Al2O3 catalyst. The Co/ γ-Al2O3 catalysts promoted with Pt, Ru or Pd were prepared by sequential impregnation method and their cat alytic performance for FTS was investigated. X-ray diffraction (XRD), temperatu re-programmed reduction (TPR) and temperature-programmed surface reaction (TPS R) were used to characterize the catalysts. The addition of small amounts of nob le metal Pt, Ru or Pd could decrease the reduction temperature of both the surfa ce active Co3O4 and the inactive cobalt oxide species that had a strong int eraction with the support. TPR results suggested that hydrogen spillover from th e active sites of promoter to cobalt oxide clusters could promote its reduction. Cobalt dispersion was improved by the addition of noble metals to Co/ γ-Al 2O3 catalyst. The improvement in the reducibility o f catalyst and the cobalt dispersion contributed greatly to the high overall act ivity of the promoted catalysts for FTS. The activity of various catalysts f ollo wed the order Co-Pt/ γ-Al2O3Co-Ru/ γ-Al2O3Co-Pd/ γ-A l2O3Co/ γ-Al2O3. TPSR results provided further evidence that th e addition of noble metal promoters could enhance the CO dissociation on the cat alysts, and thus significantly increased the hydrogenation activity of the ads orbed CO.
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