Product distribution change in the early stages of carbon monoxide hydrogenation over cobalt magnesium Fischer-Tropsch catalyst

Abstract

The catalytic hydrogenation of carbon monoxide, known as the Fischer-Tropsch process, is a technologically important, complex multipath reaction which produces long chain hydrocarbons. In order to access the initial kinetics and the mechanism, we developed a reactor that provides information under non-steady state conditions. We tested a CoMgO catalyst and monitored the initial product formation within 2s of exposure to CO as well as the time dependence of high molecular weight products (in a 60s window) and found drastic changes in the product selectivity. The probability for forming branched isomers (C4 and C5) peaks in the first 25s, and within that time frame no unsaturated products were detected. The subsequent decline (at ∼35 to 40s) of branched isomers coincides with the detection of olefins (fromC2 to C5) and the change in carbon coverage at the surface of the catalyst. This indicates a change in the reaction pathway.