Comparative Study on Structures and Energetics of NO_x, SO_x, and CO_x Adsorption on Alkaline-Earth-Metal Oxides

Abstract

Embedded cluster models of the (001) terrace site have been used to determine adsorption structures and energetics for NO x (NO 2 , NO 3 ), SO x (SO 2 , SO 3 ), as well as for CO 2 on the entire sequence (MgO-BaO) of alkaline-earth-metal oxides. The calculations have been performed at the gradient-corrected density functional level. The oxidation of NO, NO 2 , SO 2 , and CO using surface peroxo species is also considered with the aim of contributing to the understanding of car emission control catalysts based on the NO x storage and reduction concept. For all substrates, the stability of the formed surface species is in the order NO 2 -≈ CO 3 2-< NO 3 -< SO 4 2-. Between substrates the stability of the adsorbates is determined by the substrate basicity, which in turn is regulated by the lattice parameter. The resulting order is MgO < CaO < SrO < BaO. Several different bonding modes and structures are found, which differ in terms of degree of charge transfer from the substrate and how the resulting charge deficiency in the substrate is distributed among the surface ions.

Interactive CO2Adsorption on the BaO (100) Surface: A Density Functional Theory (DFT) Study

“…The larger lattice parameter provides the smaller internal Madelung stabilization, leading to the larger charge transfer. 10 Because the cubic lattice parameter of BaO (5.5 Å) is larger than that of MgO (4.21 Å) reported by experiment, the charge transfer from the BaO surface is larger than that from MgO, evidencing the relatively strong interaction of CO2 with BaO compared to other metal oxides. 19 Therefore, the DFT calculation can support the strong formation of a surface carbonate.…”

“…7 In addition, the BaO surface has a high reactivity that enables it to donate charge to the adsorbed CO2 molecule; the high reactivity can be attributed to the fact that it has a high basicity resulting from the low Madelung potential energy. 8 The quantum chemical calculation of CO2 adsorption on BaO has been already studied, 7,[9][10][11][12] but the previous studies did not examine the interactive adsorption of CO2 molecules on O sites on the BaO surface; this study investigates the interaction effect of CO2 molecules.…”

CO2 Adsorption on H2O‐Saturated BaO(1 0 0) and Induced Barium Surface Dissociation

“…10 In order to understand the adsorption mechanism, quantum mechanical studies using density functional theory (DFT) have been employed for the adsorption of gas molecules such as NO, NO 2 , CO 2 , and H 2 O on various metal oxide surfaces, with many of the studies focusing on the binding of CO 2 molecules. 8,9,[11][12][13][14] Previous studies of gas adsorption on BaO have illustrated the competitive adsorption of single gas molecules, particularly single CO 2 and single H 2 O molecules; however, these studies may not accurately describe the effect of water present on the adsorbent surfaces on CO 2 adsorption owing to the intense aggregation property exhibited by H 2 O molecules in real situations. For example, the flue gas mixtures in power plants generally contain 8-12 vol.% CO 2 and 5 vol.% water vapor after pretreatment by a wash tower at ambient conditions.…”

“…DFT has been used earlier to accurately describe the interactions between an adsorbate and mineral surfaces, 17 including CO 2 adsorption on BaO surfaces. 7,12 In order to understand the adsorption of CO 2 from the flue gas mixtures, the surface deformation and the Ba dissociation mechanisms were studied on a fully hydrated surface in order to account for the interaction of the adsorbent and the adsorbate with the water molecules. In the present work, we also assess the adsorption of CO 2 on solid adsorbents and investigate the mineralization of the adsorbent surface and the competitive adsorption of CO 2 and another species.…”

Sulfur Deactivation of NOxStorage Catalysts: A Multiscale Modeling Approach

“…Most of the existing studies targeted SO x adsorption on alkaline-earth oxides at low surface coverage [19][20][21][22]. All of them unanimously agree that both SO 2 and SO 3 readily adsorb as Lewis acids by anchoring the sulfur atom to a basic oxygen site on BaO surface to form sulfite-(SO 2 adsorption) and sulfate-like (SO 3 adsorption) surface species.…”