Berlin 2018 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 111: Oxides and Insulators: Adsorption II

O 111.1: Vortrag

Freitag, 16. März 2018, 10:30–10:45, MA 041

New Insights into the Catalytic Activity of Solid Solutions: Carbon Dioxide Activation on NiMgO — •Aliaksei Mazheika, Marie-Mathilde Millet, Sabine Wrabetz, Elias Frei, Robert Schlögl, and Sergey V. Levchenko — Fritz-Haber-Institut der MPG, Berlin 14195, Germany

Ni_xMg_yO solid solutions are stable and active catalysts for dry reforming of CH₄ and CO₂ hydrogenation. Despite numerous experimental investigations, the structure of NiMgO surfaces at realistic conditions was unclear. We present a combined hybrid DFT/experimental study of CO₂ adsorption at NiMgO surfaces. The DFT calculations are performed with the HSE(α) functional, where the fraction of exact exchange α is set to 0.3 based on a comparison of the HSE(α) and CCSD(T) embedded-cluster calculations. The periodic calculations reveal that Ni_Mg defects prefer to occupy low-coordinated sites (corners and steps) at the MgO (100) surface [1]. Thus, Ni doping promotes formation of such sites during synthesis of the solid solution. Indeed, IR experiments showed that the number of undercoordinated O sites at NiMgO surfaces is significantly increased compared to pristine MgO samples. The stabilization of (110) and reconstructed octopolar (111) surfaces by Ni doping reconciles theoretical results with microcalorimetry measuremenbts of CO₂ adsorption energies. The presence of Ni at steps and corners considerably decreases CO₂ adsorption energies compared to pure MgO which prevents the carbonation and allows further chemical transformations of CO₂.

[1] A. Mazheika and S.V. Levchenko, JPCC 120, 26934 (2016)