Theoretical Study on Hg0 Adsorption and Oxidation Mechanisms over CuCl2-Impregnated Carbonaceous Material Surface

CuCl2-modified carbonaceous materials have been regarded as a kind of mercury sorbent, but the Hg-0 reaction mechanism over CuCl2-impregnated sorbent surface is still unclear. In this work, the binding mechanism of Hg-0 on CuCl2-impregnated carbonaceous material surface was investigated using hybrid density functional theory (DFT). The results indicate that the dissociation mechanism is responsible for CuCl2 adsorption over carbonaceous material sorbent surface. The active chlorine species generated from CuCl2 adsorption can significantly enhance mercury adsorption over carbonaceous material sorbent surface. Hg-0 adsorption over CuCl2-impregnated carbonaceous material surface is dominated by a chemisorption mechanism. Surface Cl and C atoms are identified as the active sites for Hg-0 adsorption on CuCl2-impregnated carbonaceous material surface. CuCl2 plays an important role in mercury adsorption on CuCl2-impregnated carbonaceous materials. CuCl2 includes the following roles: (1) CuCl2 can increase the reactivity of its neighbor adsorption sites on carbonaceous material surface; (2) CuCl2 can provide additional active sites for Hg-0 adsorption; (3) CuCl2 can provide Cl atoms for the oxidation of Hg into HgCl. Heterogeneous mercury oxidation over CuCl2-impregnated carbonaceous material surface includes four steps: He adsorption, Cl migration, HgCl2 formation, and HgCl2 desorption. HgCl2 formation is identified as the rate-limiting step of Hg oxidation on CuCl2-impregnated carbonaceous material surface.