The role of carbon pre-coating for the synthesis of highly efficient cobalt catalysts for Fischer–Tropsch synthesis

This paper investigates the role of the carbon pre-coating of silica in controlling the structure and performance of silica supported cobalt catalysts for Fischer–Tropsch synthesis. It was found that coating silica support with carbon led to stabilization of highly dispersed cobalt oxide with partial cobalt reduction during thermal treatment in inert atmosphere. The size of cobalt oxide nanoparticles decreased from 10–15 nm over the conventional silica supported catalyst prepared without carbon pre-coating to 5–6 nm over samples with high carbon content. Calcination in air of the samples prepared using carbon pre-coating led to only partial increase in the cobalt oxide nanoparticle size to 7–8 nm with uniform particle size distribution. Deep encapsulation of cobalt nanoparticles was the major reason for low activity of the catalysts containing the carbon layer. Removal of carbon layer by calcination in air resulted in a major enhancement of the catalytic performance. Higher catalytic performance was observed with the catalysts prepared with higher carbon content and containing smaller cobalt particles. The maximum FT activity was almost twice higher compared to the reference uncoated catalysts. Higher selectivity to long chain hydrocarbons and low methane selectivity were also observed.