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

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 LaCoO 3 itself has been shown to have good NO oxidation activity, and Sr substitution improves NO oxidation rates and reduces NO 2 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 CoO 2 terminated LaCoO 3 . 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 CoO 2 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 RuO 2, MgO, and Pt. The CoO 2 termination surface pathway is energetically most similar to that of Pt and is considered to be the most plausible for NO oxidation.