Effects of Pore Size of Ru-Al₂O₃ Catalysts Prepared by Alkoxide Method on Fischer-Tropsch Reaction

Abstract

10 wt%Ru-Al₂O₃ catalysts with uniform pore sizes in the range of 3-7 nm were prepared by the alkoxide method by changing the added amount of H₂O highly diluted with butanol at the gelation stage of sol-gel preparation. The prepared catalysts were used to catalyze the Fischer-Tropsch (F-T) reaction in the slurry phase under reaction conditions of T = 503 K, P = 1 MPa, H₂/CO = 2/1, and W/F = 5-10 g-catal.h/mol. The Ru crystallite size evaluated by XRD line broadening increased with pore diameter. Stable activity in the F-T reaction was obtained for more than 40 h, probably because of the uniform structure of the catalysts. CO conversion and selectivity for higher hydrocarbons increased, and selectivity for CH₄ decreased with pore size of the catalysts. The effect can be explained in terms of diffusivity of the slurry solvent and/or the products in the uniform meso-pores, suggesting that the F-T reaction results depend more on the effect of the pore size of the catalysts than the Ru particle size.