Co3O4@Mesoporous Silica for Fischer–Tropsch Synthesis: Core–Shell Catalysts with Multiple Core Assembly and Different Pore Diameters of Shell

Abstract

A series of core–shell cobalt oxide catalysts were prepared by tuning the pore diameter of mesoporous silica shell and the influence of pore dimensions on Fischer–Tropsch synthesis was studied. TEM images of core–shell 20Co3O4@MSN-x catalysts showed an increase in the silica shell porosity with increasing molar ratio of the swelling agent to tetraethyl orthosilicate used during catalyst preparation. As a result of this porosity increase, the dispersion of congregated core Co oxide particles within the shell increased, resulting in multiple core centers. Reference catalysts were synthesized using conventional supports, and the effects of pore dimensions on the activity and hydrocarbon selectivity of the reference and the prepared core–shell catalysts were compared. In the experiments performed, 20Co3O4@MSN-x catalysts showed an increase in their CO conversion and C5+ selectivity with increasing silica shell porosity. Moreover, the prepared core–shell catalysts demonstrated higher selectivity toward C5–C18 hydrocarbon fractions than SBA–15- and SiO2-supported Co oxide catalysts. This could be due to the comparatively lower diffusion limitations and less probability of readsorption of intermediates in the confined space of the mesoporous silica shell. Further, the core–shell catalysts displayed higher stability (100 h on stream) than the reference catalysts, and this was attributed to their small diffusion length and less probability of metal sintering due to a protective silica shell around Co oxide particles.