Syngas-derived olefins over iron-based catalysts: Effects of basic properties of MgO nanocrystals

Abstract

A series of Fe/MgO catalysts with well-defined exposed crystal planes were synthesized by impregnation, deposition-precipitation and ultrasonic impregnation methods. The catalysts were characterized by X-ray powder diffraction, high-resolution transmission electron microscopy, CO2 temperature-programmed desorption, H2 temperature-programmed reduction, X-ray spectroscopy and N2 adsorption-desorption isotherms. The characterization results indicate that the basicity of MgO supports strongly affect the catalytic performance of iron-based catalysts for Fischer-Tropsch synthesis. It is found that the strong basicity sites of MgO supports remain during the ultrasonic impregnation process. The intrinsic basicity of Fe/MgO catalysts enhances dissociative CO adsorption and promotes the olefin selectivity. In addition, the catalyst of iron particles on the (111) crystal planes of MgO nanosheets presents higher TOF value and olefins selectivity than that of the catalyst using the (100) crystal planes of MgO nanocubes as a support. The effect of basic properties of MgO nanocrystals facilitates CO chemisorption, suppressing H2 adsorption and olefin desorption on the corresponding Fe/MgO catalysts.