Monte Carlo simulations of the adsorption of CO2 on the MgO(100) surface.

The adsorption of CO2 gas on the MgO (100) crystal surface is investigated using grand canonical Monte Carlo simulations. This allows us to obtain adsorption isotherms that can be compared with experiment, as well as to explore the possible formation of monolayers of different densities. Our model calculations agree reasonably well with the available experimental results. We find a "low-density" adsorbed monolayer where each CO2 molecule is bound to two Mg2+ ions on the MgO substrate. We also observe the formation of monolayers of higher density, where some of the CO2 molecules have rotated and tilted to expose additional binding sites. Low-temperature simulations of both the low- and high-density monolayers reveal that these states are very close in energy, with binding energies of approximately 7 kcal/mol at T=5 K. The high-density monolayer given by our model has a density that is significantly less than the reported experimental value. We discuss this discrepancy and offer suggestions for resolving it.