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

Wenchao Ji; Yuanyuan Meng; Xingjun Fan; Xiuhua Xiao; Feiyue Li

doi:10.1016/j.chemosphere.2022.134178

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

Chemosphere. 2022 Jun:297:134178. doi: 10.1016/j.chemosphere.2022.134178. Epub 2022 Mar 1.

Authors

Wenchao Ji¹, Yuanyuan Meng², Xingjun Fan¹, Xiuhua Xiao¹, Feiyue Li³

Affiliations

¹ College of Resource and Environment, Anhui Science and Technology University, Fengyang, 233100, China.
² College of Chemistry & Chemical Engineering, Taiyuan University of Technology, Taiyuan, 030024, PR China.
³ College of Resource and Environment, Anhui Science and Technology University, Fengyang, 233100, China; Anhui Province Key Laboratory of Biochar and Cropland Pollution Prevention, Bengbu, 233400, China. Electronic address: lify@ahstu.edu.cn.

PMID: 35240146
DOI: 10.1016/j.chemosphere.2022.134178

Abstract

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.

Keywords: Adsorption; Catalytic oxidation; Density functional theory; Elemental mercury; Single-atom catalysts.