Reaction dependent particle size effects in carbon supported cobalt catalysts

摘要

Particle size effects in nanocatalysis are of growing interest. For both supported and unsupported particles (e.g. colloids) various examples are known where the catalytic performance was proven to be dependent on particle size and shape. A growing number of studies are conducted to understand the nature of these effects, which is increasingly facilitated by well defined preparation routes, support materials, surface science studies and ab-initio calculations. A major challenge in studying particle size effects is the increased reactivity of smaller particles towards the support. The use of carbon supports and especially graphite like carbon nanofibers (CNF) is expected to alleviate this problem and allows an undisturbed study of particle size effects. Here the effects of Co particle sizes are investigated for Fischer Tropsch synthesis and ethanol-steam reforming. A decrease in Co particle is accompanied with a relative increase in the amount of uncoordinated surface sites, which is likely to have a significant impact on catalysis. The two target reactions were chosen since different types of bond are involved in the rate determining step i.e. π-bond activation of CO for FT synthesis and C-C σ-bond activation for ethanol-stream reforming.