Theoretical insights into the CO/NO oxidation mechanisms on single-atom catalysts anchored H4,4,4-graphyne and H4,4,4-graphyne/graphene sheets

Abstract

Novel two-dimensional (2D) carbon-based substrates supported single-atom catalysts (SACs) have gained enormous interests. Herein, the adsorption property of single transition metal (TM) catalysts anchored at H4,4,4-graphyne (TM-H4,4,4-GY) are investigated using the first-principle calculations. The graphene substrate can provide the electron transfer to H4,4,4-GY and then improve the stability of TM atoms on H4,4,4-GY sheet (TM-H4,4,4-GY/G). Different kinds of TM adatoms and gas reactants can effectively control the electronic and magnetic properties of Mn-H4,4,4-GY and Mn-H4,4,4-GY/G systems. Four catalytic mechanisms for NO and CO oxidations are comparably analyzed via Langmuir-Hinshelwood (LH), Eley-Rideal (ER), new ER (NER) and termolecular ER (TER) reactions. The calculated results reveal that the NO and CO oxidation processes exhibit various reaction rates on different substrates. Compared with NO oxidation on Mn-H4,4,4-GY surface, the ER and LH mechanisms as the starting state for CO oxidation are energetically more favorable than other ones. On the Mn-H4,4,4-GY/G sheet, the CO oxidation processes by ER and NER mechanisms have relatively smaller energy barriers and exhibit higher reaction rates than those of NO oxidation. Therefore, the oxidation reactions of CO acts as a leading role in the first stage and the NO oxidation may happen in the second stage. These results provide an effective descriptor about geometric structure, electronic, magnetic, gas sensoring and catalytic properties of novel 2D carbon-based catalysts.