Citric acid assisted one-step synthesis of highly dispersed metallic Co/SiO2 without further reduction: As-prepared Co/SiO2 catalysts for Fischer–Tropsch synthesis

Abstract

Highly dispersed metallic Co/SiO2 catalysts are prepared by a novel citric acid assisted synthesis method in an argon atmosphere and directly used in Fischer–Tropsch synthesis without further reduction. CH4 and H2 derived from the decomposition of metal–citric acid complexes act as reductants for synthesizing metallic Co0 from Co2+ in the chelating complexes. Thermogravimetry, differential thermal analysis, X-ray diffraction, transmission electron microscopy, temperature-programmed reduction, H2-chemisorption, and Brunauer–Emmett–Teller methods are used to identify the catalysts, proving that cobalt species are almost completely reduced (reduction degree: 95%) to metallic Co0 and highly dispersed on the SiO2 support with small cobalt crystallite sizes (about 3nm). The activity of this proposed catalyst is about 4-times of that prepared by the conventional incipient-wetness impregnation method. However, a tremendous amount of methane and lots of CO2 are produced. This novel citric acid assisted synthesis method herein is promising for preparing highly dispersed supported metallic catalysts, especially for the catalysts which are difficult to reduce.