Reduction of NO with CO on the Co3O4(110)-B and CoO(110) Surfaces: A First-Principles Study

We employed density functional theory plus the on-site Coulomb repulsion (DFT + U) method to investigate the mechanism of NO reduction with CO on the Co3O4(110)-B and CoO(110) surfaces. The surface oxygen vacancies are first generated by CO oxidation through the Mars-van Krevelen mechanism on both surfaces and then replenished by adsorbing the NO molecule to endure the catalytic cycle. Possible reaction pathways for N-2 and N2O formation are considered, and whole reaction mechanism is identified through our calculations. It is shown that the reaction pathway involving the coadsorption structure ONNOL (Path 1 and Path 1') is identified for N2O formation on the two surfaces. The formation of N-2 proceeds via the OLNNOL dimer intermediate (Path 3) followed by two almost barrierless N-O bond scissions on Co3O4(110)-B, whereas on the CoO(110) surface, the pathway involving the reaction of the NCO intermediate with NO (Path 5') is most favorable. On the basis of the DFT results, microkinetic analysis was performed to estimate the relative product selectivity of N2O and N-2 under experimental conditions. Results were compared with experimental reports.