A promising single atom catalyst for CO oxidation: Ag on boron vacancies of h-BN sheets.

Single atom catalysts (SACs) have attracted broad research interest in recent years due to their importance in various fields, such as environmental protection and energy conversion. Here, we discuss the mechanisms of CO oxidation to CO over single Ag atoms supported on hexagonal boron-nitride sheets (Ag/BN) through systematic van der Waals inclusive density functional theory (DFT-D) calculations. The Ag adatom can be anchored onto a boron defect (V), as suggested by the large energy barrier of 3.12 eV for Ag diffusion away from the V site. Three possible mechanisms (i.e., Eley-Rideal, Langmuir-Hinshelwood, and termolecular Eley-Rideal) of CO oxidation over Ag/BN are investigated. Due to "CO-Promoted O Activation", the termolecular Eley-Rideal (TER) mechanism is the most relevant one for CO oxidation over Ag/BN and the rate-limiting reaction barrier is only 0.33 eV. More importantly, the first principles molecular dynamics simulations confirm that CO oxidation via the TER mechanism may easily occur at room temperature. Analyses with the inclusion of temperature and entropy effects further indicate that the CO oxidation via the TER mechanism over Ag/BN is thermodynamically favorable in a broad range of temperatures.