Study on the effects of oxygen-containing functional groups on Hg0 adsorption in simulated flue gas by XAFS and XPS analysis

•XPS and XAFS analysis were used to evaluate effects of OCFGs on Hg0 adsorption.•Carboxyl groups might be the potential active sites for Hg0 removal.•Gaseous HCl provides more active sites on carbon surface for Hg0 adsorption.•Gaseous SO2 competes with Hg0 on active O atoms during adsorption. The effect of physicochemical properties of activated carbon on adsorption of elemental mercury (Hg0) was investigated on a series of modified activated carbons. Heat treatment and benzoic acid impregnation were conducted to vary the oxygen functional groups on carbon surface. Hg0 adsorption experiments were run in a fixed-bed reactor at 140 °C. Surface characteristics of carbon samples were studied by N2 adsorption, Boehm titration, X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS), respectively. The predominant mechanism of Hg0 removal was the formation of chemical bonds between Hg and various functional groups. Both XPS and XAFS analysis revealed that mercury bound on carbon surface was mainly in oxidation state. Under N2 atmosphere, the absorbed Hg was found as Hg2+, and coordinated to O atom. With the existence of HCl in simulated flue gas, Hg0 was bonded on Cl sites and HgCl2 was assumed to be the dominated form.