Computational study of NO + CO reaction on Pd(111) surface: effect of lattice sites on the adsorption and reactivity

The NO + CO reaction is considered a prototype reaction that portrays the abatement of NOx, the primary pollutant from automobile exhausts, catalyzed by metals like Pd, Pt, and Rh. The detailed mechanism of this reaction on the Pd(111) surface was devised by taking into account all probable elementary reactions with the aid of density functional theory calculations. The reaction steps under consideration include NO dissociation, N₂ formation from N-N recombination, CO₂ formation, N₂O formation, and N₂O dissociation, respectively. The adsorption energies, reaction energies, and activation energy barriers were calculated for all the elementary steps of the reaction. Depending on the lattice site, over which the intermediates of the elementary steps get adsorbed, adsorption energies vary significantly. Both N-N recombination and N₂O decomposition were identified as the reaction pathways for N₂ formation. The NO dissociation step could be regarded as the rate-determining step, bearing the highest activation energy barrier among all the elementary reactions. The reactivity of this step has been shown to increase with an increase in the surface temperature. It was also observed that N₂ formation from N-N recombination controls the overall reaction rate to a certain extent. The influence of different Pd facets on NO dissociation was scrutinized, and it was found that (100) facet exhibits a lower activation energy barrier than (111) metal surface. The higher activity of (100) surface was explained with the help of the density of states plots.

Graphical abstract

The model reaction NO + CO has been studied in detail on Pd (111) surface to understand Three Way Catalytic (TWC) converters. NO dissociation step was found to be the RDS. The surface temperature has been shown to affect the reactivity of the RDS. Pd(100) could be used for better performance.