Pt,Ru和Pd助剂对F-T合成中Co/γ-Al_2O_3催化剂性能的影响

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

采用浸渍法制备了添加贵金属Pt,Ru和Pd助剂的Co/γ-Al2O3催化剂,并考察了它们在F-T合成反应中的催化性能.结果表明,添加贵金属助剂可以显著提高Co/γ-Al2O3催化剂的催化活性.XRD和TPR表征结果表明,贵金属助剂不但可以使催化剂的金属分散度增加,而且可以通过氢溢流促进催化剂表面活性相的Co3O4以及与载体Al2O3有相互作用的非活性相钴氧化物物种的还原,从而改善催化剂的还原性能.TPSR结果进一步表明,添加贵金属助剂后催化剂对CO的吸附解离能力增强,从而使吸附态CO的加氢活性提高.

Noble metals such as Pt, Ru and Pd have been known to improve the reducibility of Co/γ-Al2O3 catalyst for Fischer-Tropsch synthesis （FTS）. However, little is known about their difference in promoting the reduction of cobalt oxide and their other promoter action to the Co/γ-Al2O3 catalyst. In this study we investigated the effects of different noble metals on the properties of the Co/γ-Al2O3 catalyst. The Co/γ-Al2O3 catalysts promoted with Pt, Ru or Pd were prepared by sequential impregnation method and their catalytic performance for FTS was investigated. X-ray diffraction （XRD）, temperature-programmed reduction （TPR） and temperatureprogrammed surface reaction （TPSR） were used to characterize the catalysts. The addition of small amounts of noble metal Pt, Ru or Pd could decrease the reduction temperature of both the surface active Co3O4 and the inactive cobalt oxide species that had a strong interaction with the support. TPR results suggested that hydrogen spillover from the active sites of promoter to cobah oxide clusters could promote its reduction. Cobalt dispersion was improved by the addition of noble metals to Co/γ-Al2O3 catalyst. The improvement in the reducibility of catalyst and the cobalt dispersion contributed greatly to the high overall activity of the promoted catalysts for FTS. The activity of various catalysts followed the order Co-Pt/γ-Al2O3 〉Co-Ru/γ-Al2O3 〉 Co-Pd/γ-Al2O3 〉Co/γ-Al2O3. TPSR results provided further evidence that the addition of noble metal promoters could enhance the CO dissociation on the catalysts, and thus significantly increased the hydrogenation activity of the adsorbed CO.