Effect of Cobalt Particle Size on the Catalyst Intrinsic Activity for Fischer-Tropsch Synthesis

The active sites for Fischer-Tropsch synthesis are surface cobalt metal atoms. In order to obtain a high dispersion for reaction, ultra-small cobalt clusters (e.g., 1 nm) were supported on KL-zeolite using a chemical vapor deposition procedure. A Pt promoter was added to facilitate reduction of the cobalt oxide species. Upon activation in hydrogen, a high dispersion was obtained, but after exposure to realistic FT conditions in a pressurized continuously stirred tank reactor reactor, XANES and EXAFS results indicate that the fine cobalt clusters were susceptible to reoxidation, resulting in adverse activity and selectivity (30-37 % CH4 and 3.5-4.0 % CO2 on a C% basis).