Effect of different alumina supports on performance of cobalt Fischer-Tropsch catalysts

Four identically-prepared 20 wt% cobalt/0.15 wt% ruthenium Fischer-Tropsch catalysts, supported on different aluminas, were synthesized by incipient wetness impregnation, characterized, and compared based on their performance under standard Fischer-Tropsch synthesis conditions. Three alumina supports were obtained from commercial sources (Sasol, St. Gobain, and Alfa Aesar), while the fourth was made using a published technique that included 5 wt% silica. The silica-stabilized alumina catalyst produced superior Fischer-Tropsch rates of 49 mmol CO/gcat h, compared to the other catalysts on the commercial supports with rates of 26–39 mmol CO/gcat h. The improved performance of the silica-stabilized alumina support compared to the commercially available aluminas is ascribed to a bimodal pore structure with larger average diameters and enhanced thermal stability. The support can be thermally treated to higher temperatures (e.g., 1100 °C) without transformation into α-alumina, allowing dehydroxylation of the surface prior to impregnation to stabilize a nearly ideal dispersion of cobalt crystallites.