Density Functional Theory Study of Elemental Mercury Immobilization on CuSe(001) Surface: Reaction Pathway and Effect of Typical Flue Gas Components

Abstract

The lack of a fundamental understanding of microcosmic reaction mechanisms for elemental mercury (Hg0) accommodation over a mineral selenide significantly impedes evaluations of their performances and potential applications for Hg0 adsorption from coal combustion flue gas. Hence, in this work, Hg0 adsorption profiles and conversion pathways were established for heterogeneous Hg0 conversion over an efficient and cost-effective mineral selenide, i.e., copper selenide (CuSe). Hg0 was found to be first physiosorbed by Cu-top sites over an intact CuSe(001) surface to form a Hg–Cu amalgam, which was then converted into stably chemisorbed mercury selenide (HgSe) when encountering surface active ligands such as Se monomer. The reaction pathway for Hg0 adsorption and transformation over CuSe(001) surface was Hg0 → Hg–Cu → HgSe. This proposed road map for Hg0 conversion was further proven by experimental results, in which the formation of Hg–Cu amalgam over CuSe surface was observed. The influences of typical coal combustion flue gas such as oxygen (O2), sulfur dioxide (SO2), and water vapor (H2O) on Hg0 capture over the CuSe(001) surface were also investigated. O2 was found to exhibit negligible influence on Hg0 removal, while SO2 and H2O had slight detrimental impacts on the physisorption stage of Hg0 on the Cu-top site. These results were also cross-checked by experimental observations to fully justify the accuracy of the predictions. This work thus gives in-depth microcosmic understandings on Hg0 removal over CuSe and guides further design of efficient CuSe based sorbent for Hg0 capture from coal combustion flue gas.