NO-CO Reaction Over Metal-supported Ultrathin Oxide Films: Evaluating Novel Catalysts by Density-functional Theory Calculations

An ultrathin oxide film supported on a metal substrate (Figure 1) sometimes exhibits extraordinary catalytic activities. To explore the potential of such structures as automotive exhaust catalysts, we have examined NO-CO reaction over oxide/metal slab models by plane-wave density-functional theory calculations. This article summarizes our computational results for TiO2/Ag and ZiO(2)/Cu slabs (Figure 2). For both systems, we found that NO can be adsorbed and activated on the cationic site of the oxide by receiving electronic charge from the metal (Figure 4). The activated NO specks then dimerizes to form ONNO (Figure 5). This ONNO decomposes into N2O and O (Figure 5), and N2O then decomposes into N-2 and O (Figure 6). The O adatoms left on the surface react with CO to form CO2, thus completing the catalytic cycle (Figure 7). The calculated energy bathers and adsorption energies indicate the superiority of ZrO2/Cu compared to TiO2/Ag. This difference can be attributed to a difference in charge on the cations and a difference in inter-cation distances.