Bimodal Porous Co-Ir-SiO₂ Catalysts Prepared by Sol-gel Process with Alkoxide for Fischer-Tropsch Synthesis

Abstract

Bimodal porous catalysts were prepared by modifying the surface of macro-porous silica (Q-10, Q-30 and Q-50) with 20 wt%Co-0.5 wt%Ir-SiO₂ prepared by the alkoxide method, and used for the Fischer-Tropsch synthesis in the slurry phase. The bimodal pore structure was confirmed by the pore size distribution, BET surface area, and pore volume of the catalysts. The bimodal catalysts showed high and stable activity for more than 70 h of the reaction, with reducing the using amounts of expensive alkoxide. The high activity indicates that the surface of the alkoxide catalyst (Co-Ir-SiO₂) efficiently participates in the reaction. The olefin selectivity increased with the macro-pore size of the bimodal catalysts. The higher selectivity was explained in terms of the high diffusivity of products and/or slurry solvent within the macro-pores of the bimodal catalysts. Consequently, an olefin/paraffin ratio of 0.9 in the C₂-C₄ products was obtained over the bimodal catalyst with the composition of [Co-Ir-SiO₂] : [Q-50] = 1 : 3 by weight.