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O: Fachverband Oberflächenphysik

O 72: Oxide and Insulator Surfaces: Adsorption I

O 72.7: Vortrag

Mittwoch, 22. März 2017, 12:00–12:15, WIL C107

The effect of Ni substitutional defects on the structure and chemical properties of MgO surfaces — •Aliaksei Mazheika and Sergey V. Levchenko — Fritz-Haber-Institut der MPG

Ni-MgO solid solutions are promising materials for catalytic reduction of CO₂ and dry reforming of CH₄. To explain the catalytic activity, an ab initio study of Ni-substitutional defects in MgO (Ni_Mg) has been performed. At first, the validation of the theory level was done. We compared results of CCSD(T) embedded-cluster calculations of Ni_Mg formation energies and adsorption energies of CO, CO₂ and H₂ on them to the HSE(α) hybrid DFT functional with the fraction of the exact exchange α varied between 0 and 1 [1]. HSE(0.3) was found to be the best compromise in this study. Our periodic HSE(0.3) calculations show that Ni_Mg defects are most stable at corner sites, followed by steps, and are least stable at (001) terraces. Thus, Ni-doping stabilizes stepped MgO surfaces. The dissociative adsorption of H₂ on the terrace is found to be endothermic (+1.1 eV), whereas on (110) surface with Ni_Mg it is highly exothermic (−1.6 eV). Adsorbed CO₂ is also significantly stabilized (−0.6 vs. −2.2 eV). These findings explain recent microcalorimetry measurements of H₂ and CO₂ adsorption at doped Ni-MgO samples [2].—[1] A. Mazheika and S.V. Levchenko, DOI: 10.1021/acs.jpcc.6b09505; [2] A. Mazheika, M.-M. Millet, S. Wrabetz, A. Tarasov, E. Frei, S.V. Levchenko, A. Trunschke and R. Schlögl, manuscript in preparation.

This work was funded by the UNICAT cluster of excellence.