La2O3对费-托合成沉淀铁催化剂的影响

制备了一系列不同La2O3含量(100Fe/2.8Si/nLa,n=0,0.5,1,2,4,原子比)的沉淀铁费-托合成催化剂,通过原位X射线衍射、一氧化碳程序升温还原和N2吸附-脱附等手段对催化剂进行了表征.催化剂费-托反应评价在固定床反应器中进行.结果表明,少量La2O3助剂(La/Fe≤0.01,原子比)的加入显著降低了Fe2O3颗粒大小,增加了催化剂的比表面积和分散度,有利于碳化铁的形成,从而导致费-托合成催化活性的提高.随着La2O3含量的进一步增加(La/Fe≥0.02),催化剂表面大量La2O3的覆盖和LaFeO3化合物的形成降低了铁碳化物的形成,反应活性反而降低.因此,最适宜的La2O3含量为La/Fe=0.01.La2O3的加入提高了甲烷的选择性,抑制了C5+碳氢化合物的形成.

Effect of La2O3 on a Precipitated Iron Catalyst for Fischer-Tropsch Synthesis

A series of La2O3-promoted precipitated iron catalysts(100Fe/2.8Si/nLa,n=0.0.5,1,2,and 4,atomic ratio)were prepared and characterized by in situ X-ray diffraction,CO temperature-programmed reduction,and N2 adsorption-desorption.The catalytic performance for Fischer-Tropsch synthesis was studied in a fixed-bed reactor.It was found that the addition of a small amount of La2O3(La/Fe≤0.01)gave a large decrease in the particle size of Fe2O3,which increased the specific surface area and dispersion of the catalysts.This also favored the formation of iron carbides,which gave a high cataiytic activity in Fischer-Tropsch synthesis.With increasing La2O3 content(La/Fe≥0.02),a high La2O3 coverage and the formation of a LaFeO3 compound decreased the formation of iron carbides,and the reaction activity decreased.The optimum La2O3 content was La/Fe=0.01.The addition of La2O3 increased the selectivity for methane and suppressed the formation of C5+hydrocarbons.