Elucidating the reaction mechanism of cobalt-based Fischer-Tropsch Synthesis

The rational design of next-generation catalysts that will contribute to solving the impending energy and environmental challenges requires accurate description of mesoscale phenomena in catalysis. Current state-of-the-art modeling techniques mostly focus either on the nanoscale description of individual elementary reaction steps or on the macroscale to describe behavior of reactors, usually employing lumped reaction kinetics.

In Fischer-Tropsch synthesis (FTS), it is observed that the activity and selectivity towards longer hydrocarbons increases as a function of particle size until the particle diameter is about 6 nm, at which further increase of the particle diameter does not result in a significant change in activity and selectivity. Herein, it is hypothesized that the nanoparticles have to be sufficiently large in order to harbor an adequately high abundance of so-called B5 sites, which are attributed as the locus for CO dissociation and C-C coupling.

The abundance of terrace and step-edge sites on catalytic cobalt nanoparticles as a function of the particle size has recently been elucidated within our group. The effect of the surface concentration of the active sites on the overall FTS activity of cobalt nanoparticles has been studied using a simplified Langmuir-Hinshelwood kinetic model under the assumption that C-O bond scission is the rate determining step. Within this project, you will develop one or more microkinetic models that incorporate all elementary reaction steps relevant to FTS for a particular candidate active site. The kinetic parameters for the microkinetic model will be derived from state-of-the-art density functional theory calculations.

Using such models, a multi-site microkinetic model can be constructed to study the contribution of individual active sites present on a catalytic nanoparticle towards the overall activity of that particle, which enables us to get more insight in the origin of the observed structure sensitivity effect.

Figure 1: Schematic depiction of the active site in Fischer-Tropsch synthesis.

Project-specific Learning goals

General learning goals