Manganese oxide OMS-2 material, also known as alpha-MnO2, exhibits CO2 sorption hysteresis at pressures > 7 bar. Our experiments show that the hysteretic behavior strongly depends on time, temperature and pressure. To understand the atomic structures and sorption mechanism we have performed first-principles total energy calculations. The OMS-2 material has the tunnel structure, containing K+ and H2O to stabilize the structure. The computed binding energy of H2O in the OMS-2 is 0.39eV, smaller than that of K+ by 4eV, and that therefore H2O can be easily removed, but K+ remains. K+ behaves as a gate keeper, blocking the diffusion of CO2 in the OMS-2 due to high energy barrier. Increasing the concentration of CO2 can dramatically lower the energy barrier for CO2 to bypass K+. The gate-keeping behavior accounts for the observed hysteresis. Based on the experimental and computational results, a possible CO2 sorption mechanism by OMS-2 will be discussed.
Citation: American Chemical Society, Division of Fuel Chemistry, Preprints of Symposia
Pub Type: Journals
Adsorption mechanism, CO2 storage, first-principles density functional theory calculations, manganese oxide OMS-2