Density Functional Theory Studies of the Adsorption and Interactions between Selenium Species and Mercury on Activated Carbon

Abstract

Mercury and selenium are two typical heavy metal pollutants in coal combustion flue gas. The adsorption mechanism of Se0 and SeO2 over an activated carbon (AC) adsorbent and the specific role of selenium species in Hg0 elimination were systematically studied by density functional theory calculation. The adsorption complex structures of a single Se0 atom and SeO2 molecule on the AC surface were optimized. The adsorption energy in a range of −238.97 to −545.80 kJ/mol indicated that chemisorption was the main adsorption mechanism. The adsorption properties of multiple Se0 atoms and SeO2 molecules on the AC surface were studied, and the most possible adsorption pathway was given. Multi-Se0 atoms preferred to adsorb on neighboring active sites of the AC surface to share their atomic orbitals. Instead, multi-SeO2 molecules preferred to occupy the active sites of the AC surface without any interaction. The multicomponent adsorption processes of Hg0 and selenium species on the AC surface were studied by calculating adsorption energies, electron charge transfer, and atomic bond populations. For the coadsorption of Hg0 and Se0, they preferred to adsorb on different carbon atoms in a separate way. In contrast, SeO2 tends to decompose into Se and SeO ions, and Hg0 can achieve stable configuration through interacting with the SeO ion and AC surface with an adsorption energy of −354.92 kJ/mol. This study indicated future potential for applying activated carbon in multicomponent adsorption of selenium and mercury in coal combustion flue gases.

Sulfur Dioxide Promoted Mercury Fast Deposition over a Selenite-Chloride-Induced Surface from Wet Flue Gas

“…Based on the reaction mechanism about catalytic oxidation of Hg 0 , the commonly used Deacon reaction (2HCl + 1/2O 2 → H 2 O + Cl 2 ) on oxide-based catalysts that generates active Cl* can realize the fast-trapping of Hg 0 ; , however, the production of Cl* was suppressed under SO 2 and the demercury product HgCl 2 was easily desorbed from the catalyst surface into the downstream acidic wastewater . Another active species, the elemental selenium (Se 0 ), was indicated to perform high affinity toward Hg 0 and better SO 2 resistance. , However, it should be highlighted that the stable form of Se 0 consists of helical polymeric chains, of which the Se–Se bonds are strong and hard to break, resulting in poor stability of the adsorbed Hg 0 at high temperature. , Therefore, how to construct such induced surfaces that efficiently utilize the Se and Cl should be further investigated. Considering that SO 2 can drive the in situ reduction of high valence Se­(IV) to Se 0 under wet conditions, this can prevent its direct agglomeration into a stable chain structure.…”

Construction of a Thermally Stable Low-HgCl2 Catalyst via Chalcogen Bonding and Its Enhanced Activity in Acetylene Hydrochlorination

“…However, no reports have studied the chalcogen bonding (ChB) with HgCl 2 molecules to enhance the catalytic activities in acetylene hydrochlorination. Particularly, a single Se atom is more likely to be adsorbed between two carbon atoms with an adsorption energy of −487.82 kJ/mol, which is more negative than that of HgCl 2 (−44.6 kJ/mol) . Then, chalcogens could be used to strengthen the connection between mercury and the carrier at the same time to achieve high stability.…”

“…Particularly, a single Se atom is more likely to be adsorbed between two carbon atoms with an adsorption energy of −487.82 kJ/ mol, which is more negative than that of HgCl 2 (−44.6 kJ/ mol). 29 Then, chalcogens could be used to strengthen the connection between mercury and the carrier at the same time to achieve high stability. On this basis, we focused on the effect of coordination of Hg, Cl, and chalcogen elements (S, Se, and Te) on the catalytic performance, and the comparative experiment was carried out by replacing Se with S and Te to clarify the effect of chalcogens on the low-mercury catalysts.…”

Coordinatively Unsaturated Selenides over CuFeSe2 toward Highly Efficient Mercury Immobilization

“…However, the lack of active ligands capable of rapidly immobilizing Hg 0 over AC surface was identified as the primary reason accounting for the surplus injection of ACs in real-world applications . In addition, the adsorption energies of Hg 0 over many ACs were approximately 50 kJ·mol –1 . , The mercury-laden ACs captured by ESP are generally retained in the ash hopper of ESP for a relatively long time. As a result, the captured mercury on ACs would redischarged into flue gas owing to the weak binding affinity of ACs to mercury.…”

“…12 In addition, the adsorption energies of Hg 0 over many ACs were approximately 50 kJ•mol −1 . 13,14 The mercury-laden ACs captured by ESP are generally retained in the ash hopper of ESP for a relatively long time. As a result, the captured mercury on ACs would redischarged into flue gas owing to the weak binding affinity of ACs to mercury.…”