(682c) Molecular Simulation of Combined Chemi- and Physi-Sorption of Carbon Monoxide on Cobalt in the Presence of Supercritical Hexane

The use of supercritical fluid (SCF) solvents to enhance heterogeneous catalysis is growing, with several examples focused on energy and fuel applications. One such application is the use of supercritical hexane to enhance the overall catalytic chemistry of Fischer-Tropsch (FT) synthesis for the production of liquid hydrocarbon fuels. Catalytic reaction engineering experiments have demonstrated that FT synthesis in SCF hexane has several advantages over conventional FT processing, including improved heat management, reduced catalyst deactivation via coking, faster reaction rates, and better product selectivity. More recent molecular simulation studies have revealed unique and relevant aspects to adsorption in/with SCF fluids, including crossover behavior (from adsorption to depletion) for SCF hexane physisorption on a cobalt FT catalyst [1] and a density dependence for the free energy of carbon monoxide chemi-sorption on cobalt which correlates to the bulk SCF hexane isothermal compressibility [2].

This work explores the combined chemical and phase equilibrium present during chemisorption within a SCF solvent environment via reactive Monte Carlo simulations. A previously developed Morse potential for carbon monoxide interaction with cobalt [2] has been added into an existing Monte Carlo code [3], to allow for the proper energetics associated with carbon monoxide chemisorption onto cobalt. Grand canonical Monte Carlo simulations are conducted to explore the adsorption loadings and energetics of carbon monoxide and SCF hexane solvent in cobalt slit pores of varying dimensions under a range of pressure/density conditions, spanning from the ideal gas limit to SCF hexane conditions. Simulations reveal the larger loading and heat of adsorption associated with the chemisorbed CO, versus the smaller loadings and heat of adsorption associated with the physisorbed hexane solvent.

[1] Benjamin, K. M., Asiaee, A., Veer, C., Losinski, C., Gunderson, S., and Larson, T., “Monte Carlo Simulation of Near- and Supercritical Hexane Fluid and Physisorption Phase Behavior”, J. Phys. Chem. C, 2016, 120, 21336-21343.

[2] Asiaee, A. and Benjamin, K. M., “Molecular Simulation of CO Chemisorption on Co(0001) in Presence of Supercritical Fluid Solvent: A Potential of Mean Force Study”, J. Chem. Phys., 2016, 145, 084506.

[3] Martin, M. G., "MCCCS Towhee: a tool for Monte Carlo molecular simulation", Mol. Simulat., 2013, 39, 1212-1222.; http://towhee.sourceforge.net