Unravelling the effects of short pore on Fischer-Tropsch synthesis and its role as selectivity controller

Abstract

Ordered mesoporous silica with different pore lengths were synthesized and used as supports for cobalt catalysts in the Fischer-Tropsch (FT) synthesis. The effects of pore length on the product distribution and activity were meticulously investigated, while keeping the cobalt crystal size and pore diameter almost identical. Especially, the catalysts with short pore exhibited significantly increased CO conversion, increased C2-C4 paraffin ratio, and decreased C5+ hydrocarbon selectivity. The short pore was found to provide much faster access rate to reactants, whereas it significantly decreased reaction time due to the shortened residence time in the pore. In situ diffuse reflectance infrared Fourier transform (DRIFT) study revealed that the bridge-type CO adsorption mode was less favored than the linear adsorption mode. This feature reflected decreased propagation probability, and lower selectivity for long-chain hydrocarbons than the Anderson-Schulz-Flory (ASF) distribution predicted. Therefore, catalysts with controlled pore length can be utilized as a selective FT catalyst, exhibiting non-ASF feature. In addition, ordered mesoporous aluminosilicate supports having relatively large mesopore were prepared to see the effects of pore confinement and pore length as well.