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 N-2 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 catalytic 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.