Impact of cobalt catalyst carburization on Fischer‐Tropsch micro‐kinetics

Abstract

Recent models of the Fischer‐Tropsch synthesis are able to predict quite accurately the catalyst's initial activity and selectivity. However, these micro‐kinetic models rarely consider the performance loss with time on stream and in particular the heavy product selectivity loss. In this study, a deactivation model at the micro‐kinetic scale is proposed to represent the effect of carburization on Fischer‐Tropsch catalysts performances. Comparison of different mechanisms revealed that termination reactions were the most affected by cobalt carbide formation, before reactants adsorption or chain growth. Both activity and selectivity decline could be accurately described using linear and second‐order power laws expressions of active sites concentration and termination kinetic rate constants. The obtained model predicts a monotonous evolution of activity and selectivities from 10% to 80% carburization, above which an important increase of olefin selectivity is observed. The model did not indicate any change of the surface coverages after carburization.