Insights into an abnormal behavior of AC for mercury removal: Synergistic effect of acid sites and hydrogen-bonded microenvironment on AC surface

Thermal pretreatment reduces rather than improves Hg 0 removal of AC. • Acidic functional groups serve as the active centers for Hg 0 oxidation. • Hydrogen-bonded microenvironment enhances catalytic activity of acidic sites. • Synergy of acid sites and microenvironment enables high-efficiency Hg 0 removal. Activated carbon injection is a mainstream technology for elemental mercury (Hg 0 ) removal from flue gas. This study investigates an abnormal phenomenon that thermal pretreatment of AC reduces rather than improves its Hg 0 removal efficiency, and systematically elucidates the underlying mechanism. The results demonstrate that acidic sites (e.g., carboxyl groups) on the AC surface serve as the active centers for the catalytic oxidation of Hg 0 , while the hydrogen-bonded microenvironment formed by adsorbed H 2 O molecules significantly enhances the acidity strength and catalytic activity of the acidic sites. Removal of the hydrogen-bond microenvironment severely reduces Hg 0 removal performance, whereas supplementation of H 2 O or other hydrogen-bond donor molecules effectively recovers the Hg 0 removal efficiency. At medium-to-high temperatures, constructing a thermally stable microenvironment (e.g., using benzoic acid) significantly improves the Hg 0 removal efficiency of AC. Based on this synergistic mechanism, the acid-treated and benzoic acid-modified AC (AC-H-150-benzoic acid) could achieve an initial Hg 0 removal efficiency of 75.8% at 150 °C. This work reveals the synergistic effect between acidic sites and the hydrogen-bonded microenvironment on AC for Hg 0 removal, providing new insights for the rational design of high-performance Hg 0 removal adsorbents. Download: Download high-res image (182KB) Download: Download full-size image