Effect of Shell Thickness on the Catalytic Performance of Co@SiO2 Core-Shell Catalysts for Fischer–Tropsch Synthesis

Abstract

Fischer–Tropsch synthesis (FTS) is an essential strategy for mitigating the energy crisis, combating climate change, and promoting sustainable development. Supported cobalt-based catalysts exhibit significant activity in FTS, but their product selectivity requires further optimization. In this paper, Co@SiO₂ catalysts with core-shell structure were prepared by hydrothermal synthesis. The effect of the SiO₂ shell thickness on the catalytic performance of FTS was explored by varying the amount of ethyl orthosilicate (TEOS) added with stabilizer polyvinylpyrrolidone (PVP). Among them, the catalyst CS3 achieved the greatest number of cobalt active sites, the highest CO conversion (77.2%), and C₅₊ selectivity (84.3%) with a high C₅-C₁₁ proportion in the C₅₊ product. Characterizations of the catalysts were performed to examine their morphology and physicochemical properties. It was observed that the dispersion of cobalt species improved with increasing shell thickness within a certain range, promoting the reduction of cobalt species. However, the formation of Si-OH groups because of the hydrolysis of excess TEOS clogged catalyst pores, consequently diminishing the catalytic activity in FTS. Compared with the CS3-PVP0 catalyst without stabilizer PVP added, the catalyst CS3 with PVP added exhibited obvious ordered morphology, making CO conversion significantly enhanced. This is attributed to the role of inert carbon in PVP, which not only boosts the reducibility of cobalt species but also enhances the surface hydrophobicity of the mesoporous SiO₂ material.