DFT Analysis of NO Oxidation Intermediates on Undoped and Doped LaCoO3 Perovskite

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• 作者：Michael W. Penninger ; Chang Hwan Kim ; Levi T. Thompson ; William F. Schneider
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：September 3, 2015
• 年：2015
• 卷：119
• 期：35
• 页码：20488-20494
• 全文大小：476K
• ISSN：1932-7455

文摘

Perovskites are of interest as low-cost replacements for Pt-based NO oxidation catalysts. While the mechanism of Pt-catalyzed NO oxidation is fairly well understood, such is not the case for the oxides. The perovskite LaCoO₃ itself has been shown to have good NO oxidation activity, and Sr substitution improves NO oxidation rates and reduces NO₂ inhibition. In this work, we report density functional theory (DFT) results for the adsorption of NO_x (x = 1, 2) to the undoped and Sr doped (100) LaO and CoO₂ terminated LaCoO₃. Further, we used first-principles thermodynamic models to determine the most common surface species under NO oxidation conditions. Nitrates and adsorbed NO are most stable on the LaO and CoO₂ terminations, respectively. We explored the relative free energies of surface and vacancy-mediated pathways for NO oxidation. The vacancy-mediated pathways suffer from energetically costly removal of surface oxygen, while the surface pathway is most feasible for NO oxidation to occur. The perovskite surface free energy reaction pathway is compared to RuO₂, MgO, and Pt. The CoO₂ termination surface pathway is energetically most similar to that of Pt and is considered to be the most plausible for NO oxidation.