DFT Study of CO₂ Activation on Doped and Ultrathin MgO Films.

Abstract

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 –, and carbonate, CO3 2–. 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.

Initial stages of CO2 adsorption on CaO: a combined experimental and computational study

“…25 For CO 2 on MgO(001), it has been shown that electron transfer from subsurface Mo can affect the preferred binding of CO 2 as surface carboxylate rather than carbonate. 26,27 In this combined experimental and theoretical study, we report on CO 2 adsorption on well-characterized CaO thin films grown on metal substrates, focusing on the initial stages of adsorption in the low coverage regime. Using infrared reflection-absorption spectroscopy (IRAS), temperature programmed desorption (TPD), microcalorimetry, and quantum chemistry calculations, we show that CO 2 strongly adsorbs as monodentate carbonates first on step edges, followed by terrace sites.…”

H2 Adsorption on Wurtzite ZnO and on ZnO/M(111) (M=Cu, Ag and Au) Bilayer Films

“…For ionic oxides, such as MgO, or ZrO 2 , H 2 dissociation occurs preferentially via heterolytic splitting, forming an hydroxyl O 2− H + group and hydride M n+ H − group (M is the metal cation). On the other hand, H 2 prefers to dissociate homolytically on reducible oxide, such as TiO 2 , CeO 2 forming two O 2− H + groups and two extra electrons usually localized in the d states of neighboring transition metal atoms. Sometimes, the electronic properties of an oxide can be completely changed when this is obtained in nanostructured form, either free‐standing ultrathin films, ultrathin films deposited on metal supports, or simply oxide nanoparticles.…”

“…On metal oxide surfaces, the dissociation of H 2 is mostly depending on the nature of the oxide. For ionic oxides, such as MgO, [33,34] or ZrO 2 , [35,36] [37] CeO 2 [38] forming two O 2À H + groups and two extra electrons usually localized in the d states of neighboring transition metal atoms. Sometimes, the electronic properties of an oxide can be completely changed when this is obtained in nanostructured form, either free-standing ultrathin films, ultrathin films deposited on metal supports, or simply oxide nanoparticles.…”

“…Sometimes, the electronic properties of an oxide can be completely changed when this is obtained in nanostructured form, either free-standing ultrathin films, ultrathin films deposited on metal supports, or simply oxide nanoparticles. This has been illustrated by the study of H 2 adsorption and dissociation on free-standing and metal supported ZrO 2 [35] or TiO 2 films [37] and ZrO 2 nanoparticles. [39] The dissociative adsorption behaviors of H 2 on free-standing films oxide is reversed on metal supported films.…”

Effects of the cooperative interaction on the diffusion of hydrogen on MgO(100)

“…Due to theoretical and experimental advantages, MgO surfaces have become a prototypical model system for detailed investigations of different features in catalysis such as basicity testing, charge transfer, CO 2 activation, and H 2 O dissociation on simple doped or thin film MgO. [1][2][3][4][5][6][7] The presence of hydrogen on solid surfaces is of key importance for several processes like heterogeneous catalysis, hydrogen storage fuel cells, and sensors. [8][9][10] Understanding the adsorption of hydrogen is important for various processes such as the dissociation/recombination of hydrogen, direct X-H dissociation of molecules (e.g.…”