Theoretical insights into the oxidation of elemental mercury by O2 on graphene-based Pt single-atom catalysts

Pt single-atom catalysts (SACs) exhibit good performance for oxygen activation, which plays a significant role in the oxidation of Hg0 by O2 in flue gas. Density functional theory calculations are carried out to reveal the interfacial behavior of Hg0, O2 and HgO on Pt SACs (single vacancy and 3 N doped defected graphene, Pt/SV-GN and Pt/3N-GN) and the mechanism of Hg0 oxidation by O2. The results show that the flue gas components are chemically adsorbed and bond with the Pt of the Pt SACs with adsorption energies ranging from -0.555 to -5.154 eV. Electronic structure analysis indicates that Hg0 is an electron donor and transfers 0.114-0.128 e- to the Pt SACs. Both O2 and HgO are electron acceptors and obtain 0.184-0.303 e- from the slabs. Pt/3N-GN has a higher activity than that of Pt/SV-GN for these three flue gas compositions. The significant charge transfer and orbital hybridization between the gas molecules and atomic catalysts lead to a strong interaction. Furthermore, the Pt-3C and Pt-3N states can increase the band gap compared with pristine graphene, corresponding to 0.195 and 0.129 eV, respectively. Narrow band gaps indicate easier electron excitation properties, which enhance the activity of the reaction. Through a transition states (TSs) search, the lower O2 dissociation barrier is found to correspond to the lower Hg0 oxidation barrier. Pt/3N-GN has higher catalytic oxidation performance for Hg0 in the presence of O2, with a rate determining reaction barrier of 2.016 eV. Compared to traditional selective catalytic reduction and Fe-based SACs, the Pt/3N-GN catalyst has a good oxidation reaction capability with a lower activation energy, indicating that it is a promising catalyst for the oxidation of Hg0 by O2.