Activating H<sub>2</sub>S into Polysulfide by Citric Acid-Induced Surface-Active Oxygen in Cu-OMS-2 for Enhanced Oxidation of Hg<sup>0</sup> at Ambient Temperature
Yuqin Zhang, Tiantian Liu, Bing Wang, Yahui Wang, Hui Wang, Shengji Wu, Weiren Bao, Liping Chang, Jiancheng Wang
Abstract
Capturing mercury (Hg 0 ) in raw natural gas is crucial for the stable operation of natural gas purification systems. However, achieving direct oxidation removal of Hg 0 in a reducing atmosphere at ambient temperature presents a significant challenge. In this study, we designed a Cu-doped OMS-2 sorbent, synthesized with citric acid (CA) assistance, which demonstrated exceptional Hg 0 removal performance in simulated natural gas at ambient temperature. The sorbent achieved 97.0% Hg 0 removal efficiency under a space velocity of 72 × 10 4 h –1 when the CA ratio was 0.05. As a carboxyl-rich organic complexing and reducing agent, CA promoted the introduction and dispersion of Cu ions, thereby forming more Mn–O–Cu units. The resulting charge transfer of Mn–O–Cu units further facilitated oxygen vacancy (O v ) formation and lattice oxygen (O latt ) activation, promoting the transformation of gaseous H 2 S into polysulfide ( S n 2– ) species. The accumulation of electrons around active S n 2– groups accelerated electron transfer with Hg 0 via an Eley–Rideal mechanism. This work provides new insights into the design of highly oxygen-active sorbents under reducing conditions and contributes to a deeper understanding of the adsorption and oxidation mechanisms of Hg 0 .