Stability and Catalytic Performance of Single-Atom Supported on Ti CO for Low-Temperature CO Oxidation: A First-Principles Study.

Based on first-principles calculations, the potential of Ti CO monolayer (MXene) as a single-atom catalyst (SAC) support for 3d transition metal (TM) atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) is studied for CO oxidation. We first screen the support effect according to the stability of a single metal atom and find that Sc and Ti supported on Ti CO have stronger adsorption energy than the cohesive energy of their bulk counterparts and therefore, we selected Sc and Ti supported on Ti CO for further catalytic reactions. The stability and the potential catalytic reactivity are verified by electronic structure and charge transfer analysis. Both Eley-Rideal (ER) and Langmuir-Hinshelwood (LH) mechanisms are considered in this study, and lower energy barriers of 0.002 and 0.37 eV were found in the ER mechanism compared to the LH mechanism, which are 0.25 and 0.34 eV for Sc and Ti catalysts, respectively. Moreover, kinetic ER and LH mechanisms are favorable for both Sc- and Ti/Ti CO because of the comparable energy barrier to other metals and SAC supported on 2D materials. However, Ti/Ti CO catalyst is thermodynamically unfavorable. Based on these calculations, we propose that Sc supported on Ti CO is the best catalyst for CO-oxidation. The current study not only broadens the scope of the single-atom Sc catalyst but also extends the consideration of MXene support for catalyst optimization.