Modification of mesoporous alumina as a support for cobalt-based catalyst in Fischer-Tropsch synthesis

Abstract

The high surface area, large pore volume and pore diameter mesoporous alumina was synthesized using pluronic F127 as a structure-directing agent. This material was employed as a support for the cobalt catalyst in Fischer-Tropsch Synthesis (FTS). During the catalyst synthesis, impregnation of cobalt nitrate aqueous solution caused a collapse in the structure and a drastic decline in the textural properties of the mesoporous alumina. Organic solvents such as acetone and ethanol were employed instead to realize their impact on the corresponding cobalt catalysts stability. The synthesized catalysts were characterized using BET, XRD, TEM, TPR, and H2 chemisorption. The catalysts prepared using organic solvents were found to retain the textural properties of the mesoporous alumina. The process conditions including temperature, pressure, and GHSV were optimized adopting Taghuchi experimental design. Then, all catalysts were tested in FTS utilizing syngas with H2/CO ratio 2.0, at optimized conditions of 230°C, 400psi, and GHSV of 900h−1. The Co/γ-Al2O3 catalyst was also synthesized and tested in FTS for the comparison study. The physico-chemical properties of the synthesized catalysts were correlated with their performances in FTS. The mesoporous alumina supported cobalt catalyst using ethanol as a solvent in its preparation was found to be the most stable in the series and it showed 8.3% higher CO conversion, 3.3% higher C5+ selectivity, and 2.7% lower CH4 selectivity as compared to those shown by Co/γ-Al2O3 catalyst. Higher cobalt loadings of 22.5 and 30wt% were also prepared using ethanol solvent and examined in FTS. Doubling the cobalt content from 15 to 30wt% of the catalyst resulted in stable catalyst with 23% increase in the hydrocarbon yield and 4% improve in C5+ selectivity.