Chromium Single-Atom Catalyst with Graphyne Support: A Theoretical Study of NO Oxidation and Reduction

Catalytic mechanisms and bonding analysis of NO oxidation and reduction on Cr single-atom catalysts (SAC) dispersed on the graphyne (GY) surface have been systematically investigated using the first-principles theoretical methods. GY is a decent support for isolated transition-metal (TM) atom catalysts because the most active sp-hybridized carbon atoms exist on the GY surface. All the single TM atoms are trapped into the void of the GY surface and existed in the isolated form. The molecular geometries and adsorbate binding energies of NO@TM-GY, ON@TM-GY, and O-2@TM-GY configurations are determined. We find that the Cr-GY is the most promising SAC for NO oxidation and reduction compared with the other TM-SACs. Herein, we report an efficient NO oxidation and reduction catalyzed by Cr-GY at ambient temperature. We find that Cr-GY SAC is very reactive for NO oxidation and reduction at ambient temperatures with low activation barriers to the rate-determining steps for Eley-Rideal (0.87, 0.60, and 0.62 eV) and Langmuir-Hinshelwood (0.69, 0.62, and 0.84 eV) mechanisms. The Termolecular Eley-Rideal mechanism for the formation of the NO2 molecule is not thermodynamically favorable. Comparative analysis revealed that the NO reduction (0.62 eV) is more favorable than NO oxidation (0.84 eV). These findings provide valuable perceptions for design of highly efficient and selective heterogeneous SACs for NO oxidation and reduction with TMs.