Combined experimental and theoretical investigation of the CO2 adsorption on LaMnO3+y perovskite oxide

The surface interaction of CO2 with the perovskite-type oxide LaMnO3+y has been investigated by means of density functional theory calculations and experimental measurements of adsorption isotherms in the temperature range 298–473 K. A (1 0 0) oriented slab of the cubic structure was used for modeling CO2 adsorption. The reference unit cell contains alternating LaO+ layers and MnO 2 - layers; one slab is LaO+-terminated and the opposite surface is MnO 2 - terminated. A Freundlich isotherm fitted the experimental data satisfactorily. Analysis of the isosteric heat revealed an energetically heterogeneous character for the lanthanum manganite oxide surface, mainly due to the degree of heterogeneity of the adsorption center and due to the adsorbate–adsorbate lateral interactions. Considering theoretical calculations and thermodynamical approaches, two types of active sites were found to be responsible for irreversible and reversible adsorption of CO2 as a function of surface coverage and O2 treatment. Strong adsorption takes place on the surface containing La cations. The strongest adsorption is associated with surface oxygen vacancies, F s ° center. The next strongest adsorption, a flat adaptation of CO2 molecules with respect to the surface sites, with a strong binding to a surface oxygen, leads to chemisorbed carbonate species. These adsorption modes are chiefly indicative of a high basic character of the lanthanum manganite oxide surface. Several cationic sites formed by lanthanum and manganese cations are able to weakly adsorb CO2 molecules in perpendicular or bridged forms. The latter adsorption modes suggest a weak acidic character of the manganite adsorbent.