Fischer-Tropsch synthesis (FTS) which involves the conversion of CO and H<sub>2</sub> to hydrocarbons over Fe, Co, and Ru catalysts is a process critical to the success of many strategies for the conversion of natural gas, biomass, and CO<sub>2</sub> to fuels and chemicals. Despite decades of practice, the mechanisms that govern the activation of CO and hydrocarbon chain growth in FTS are still actively debated.  Herein we present rigorous kinetic and isotopic labeling studies along with first principle theoretical simulations that examine the activation of CO on supported Ru particles under working catalytic conditions.  The results show that the high CO pressures and temperatures used in FTS result in saturation coverages that are greater than 1 ML. Rigorous kinetic analysis along with detailed theoretical calculations indicate that direct CO activation is prohibited on such surface.  CO is instead activated by the assistance of chemisorbed hydrogen.  The addition of water promotes the rates of C-O activation, reduces the production of methane and increases the selectivity to C5+ intermediates by facilitating proton-coupled-electron transfer to the oxygen on the carbonyl surface intermediates. This facilitates C-O and RC-O bond scission.  The CHx* intermediates that form appear to facilitate the activation of neighboring CO* intermediates and thus promote rapid hydrocarbon chain growth.  The ratio of the rates of chain growth for Cn compared to the rates of chain termination for Cn species provide unique insights into the mechanisms for chain growth and suggest ways in which they can be controlled.

Insights into CO activation and hydrocarbon chain growth in Fischer-Tropsch synthesis

251st National Meeting (2016)

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