Facile NO-CO elimination over zirconia-coated Cu(1 1 0) surfaces: Further evidence from DFT + U calculations

Abstract In a previous publication [Catal. Lett. 147 (2017) 1827], zirconia-coated copper (Cu@ZrO2) was proposed as a potential automotive catalyst on the basis of density-functional theory (DFT) calculations. To provide further evidence, the detailed processes of NO-CO elimination over a ZrO2(1 1 0)/Cu(1 1 0) junction model have been studied using the DFT + U method. It has been confirmed that NO is adsorbed and activated on Zr4+ owing to charge transfer from the ZrO2/Cu interface. The energy barriers for NO migration were 0.46 eV and 0.77 eV along ZrO2 [1  1 ¯  0] and [0 0 1], respectively, reflecting the anisotropy of the (1 1 0) surface. Small activation energies were obtained for the elementary steps of NO-CO elimination: 2NO → ONNO → O + N2O (0.29 eV), N2O → N2 + O (0.02 eV), and O + CO → CO2 (0.11 eV). The activation energies were low, whether or not U was applied and whether the oxide film consisted of two or four (1 1 0) layers. Oxygen vacancies were stabilized by the transfer of excess charge to the Cu support. Preliminary experiments with zirconia-loaded Cu powder showed a clear improvement in three-way catalytic activities. These results show the promising potential of Cu@ZrO2 as a common-metal catalyst for NO-CO elimination.