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

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 3 nm). 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.