CHARACTERIZATION OF COBALT FISCHER-TROPSCH CATALYSTS .1. UNPROMOTED COBALT-SILICA GEL CATALYSTS

The effect of preparation conditions on cobalt-silica gel catalysts ha s been investigated by temperature-programmed reduction, differential thermal analysis, X-ray photoelectron spectroscopy, and magnetic susce ptibility measurements. The results have been correlated with the perf ormance of the catalysts for the conversion of syngas. It has been fou nd that active Fischer-Tropsch (F-T) cobalt catalysts can be partially or totally reduced to the metal phase during activation. However, red ucibility of the catalysts is a necessary but not sufficient character istic in ensuring good activity. The pH of the impregnating solution i nfluences surface charge and solubility of silica gel. Consequently, t he physical and chemical properties of the cobalt species on the surfa ce of silica gel are strongly affected by this parameter. At pH < 5 co balt deposits as a cation. At pH < 2 the silica surface is positively charged so that the dispersion of cobalt and consequently catalytic ac tivity are poor. At pH greater than or equal to 5, cobalt reacts to fo rm silicates or hydrosilicates which are irreducible. Active catalysts are shown to adsorb hydrogen by spillover on to the silica support.