Pinpointing the Active Site and Reaction Mechanism of CO Oxidation on NiO

To explore the active site and reaction mechanism of CO oxidation on metal oxides is of great significance in heterogeneous catalysis. NiO attracts a rising concern in heterogeneous catalysis due to its high performance and low cost. Nevertheless, the active sites and reaction mechanism still remain controversial due to the complexity in experiment, the limitation in characterization techniques, as well as the difficulty in searching the global reaction pathway in theory. In this work, the terrace and stepped NiO(100) with and without oxygen vacancy are established based on the Wulff construction, and the active sites and reaction mechanism are revealed at atomic level by a novel global pathway searching method. Theoretical results indicate that the coordination-unsaturated Ni ions are the active site for CO oxidation; O2 interacts with the low-coordinated Ni ions to form reactive oxygen species; then it reacts with CO to form CO2; oxygen species on stepped NiO(100) has a low barrier and sustains a catalytic cycle. The present work points out that the direction for the design and development of NiO-based catalysts with high performance is to prepare NiO catalysts with more defects and low-coordinated Ni ions. We anticipate that the approach generalized in this work can be employed to a wide range in exploring the active site and mechanism of heterogeneous catalysts.