文摘
The bonding mode of carbon dioxide with the surface of various forms of MgO has been investigated by means of density functional theory calculations. Four supports have been considered: the bare MgO(100) surface, the surface of Al-doped MgO, and ultrathin MgO/Ag(100) and MgO/Mo(100) films. Three forms of adsorbed CO2 have been investigated: physisorbed CO2, chemisorbed carboxylate, CO2鈥?/sup>, and carbonate, CO32鈥?/sup>. While on MgO(100) CO2 forms either the physisorbed species or the more stable surface carbonate, on Al-doped MgO carboxylate is the preferred species. The adsorption properties of one- or two-layer MgO films differ completely as a function of the metal support. On MgO/Ag(100) the properties of adsorbed CO2 are very similar to those of the MgO(100) surface (formation of carbonate, not of carboxylate); on MgO/Mo(100), on the contrary, both carbonate and carboxylate species can form, depending on the film thickness. On a one-layer film, both species are formed with a comparable stability, while for thicker films the carboxylate species becomes unstable. The surface of Al-doped MgO(100) exhibits similar features to that of the nondefective MgO/Mo(100) one-layer film.