PHYSICAL, CHEMICAL, AND CATALYTIC PROPERTIES OF BORIDED COBALT FISCHER-TROPSCH CATALYSTS

Unsupported and alumina-supported borided cobalt catalysts were prepared by chemical reduction of anhydrous cobalt acetate at 25{dollar}spcirc{dollar}C using B{dollar}sb 2{dollar}H{dollar}sb 6{dollar}/THF or NaBH{dollar}sb 4{dollar}/diglyme solution as the reducing agent. These catalysts were further activated in H{dollar}sb 2{dollar} at 250{dollar}spcirc{dollar}C prior to use. The physical and chemical properties of these catalysts were characterized by chemical analysis, BET surface area measurements, H{dollar}sb 2{dollar} and CO adsorption measurements, X-ray Diffraction, and Temperature Programmed Desorption of CO. The catalytic properties of these catalysts for hydrogenation of CO to hydrocarbons were investigated at 160 - 300{dollar}spcirc{dollar}C, 1 and 10 atm, and H{dollar}sb 2{dollar}/CO ratio of 2 in a differential conversion range of less than 8%.; The data show that unsupported, Na-free, borided cobalt is much more active than Na-containing borided cobalt and pure cobalt on a site basis. Similarly, CoB/Al{dollar}sb 2{dollar}O{dollar}sb 3{dollar} is more than an order of magnitude more active than Co/Al{dollar}sb 2{dollar}O{dollar}sb 3{dollar} but has similar selectivity; its selectivity for C{dollar}sb 5sp{lcub}+{rcub}{dollar} hydrocarbons, however, is very high ({dollar}>{dollar}75wt%) at low reaction temperatures (e.g. 170{dollar}spcirc{dollar}C) or at low H{dollar}sb 2{dollar}/CO ratios (e.g.{dollar}leq{dollar}1). The observed changes in catalytic and adsorption behavior are consistent with an electron-donor model in which boron atoms donate electrons to cobalt. Na was found to lower catalytic activity of cobalt while increasing selectivity for light hydrocarbons, olefins, and CO{dollar}sb 2{dollar} products.