The Fischer-Tropsch process, or the catalytic hydrogenation of carbon monoxide (CO), produces long chain hydrocarbons and offers an alternative to the use of crude oil for chemical feedstocks. The observed size dependence of cobalt (Co) catalysts for the Fischer-Tropsch reaction was studied with colloidally prepared Co nanoparticles and a chemical transient kinetics reactor capable of measurements under non-steady-state conditions. Co nanoparticles of 4.3 nm and 9.5 nm diameters were synthesized and tested under atmospheric pressure conditions and H /CO=2. Large differences in carbon coverage (Θ ) were observed for the two catalysts: the 4.3 nm Co catalyst has a Θ less than one while the 9.5 nm Co catalyst supports a Θ greater than two. The monomer units present on the surface during reaction are identified as single carbon species for both sizes of Co nanoparticles, and the major CO dissociation site is identified as the B -B geometry. The difference in activity of Co nanoparticles was found to be a result of the structure sensitivity caused by the loss of these specific types of sites at smaller nanoparticle sizes.

The Fischer-Tropsch process,orthe catalytic hydrogenation of carbon monoxide (CO), produces long chain hydrocarbons and offers an alternative to the use of crude oil for chemical feedstocks.T he observed size dependence of cobalt (Co) catalysts for the Fischer-Tropsch reaction was studied with colloidally prepared Co nanoparticles and ac hemical transient kinetics reactor capable of measurements under non-steady-state conditions.Conanoparticles of 4.3 nm and 9.5 nm diameters were synthesized and tested under atmospheric pressure conditions and H 2 /CO = 2. Large differences in carbon coverage (V C )w ere observed for the two catalysts:t he 4.3 nm Co catalyst has a V C less than one while the 9.5 nm Co catalyst supports a V C greater than two.T he monomer units present on the surface during reaction are identified as single carbon species for both sizes of Co nanoparticles,a nd the major CO dissociation site is identified as the B 5 -B geometry.T he difference in activity of Co nanoparticles was found to be ar esult of the structure sensitivity caused by the loss of these specific types of sites at smaller nanoparticle sizes.