Activating H2S into Polysulfide by Citric Acid-Induced Surface-Active Oxygen in Cu-OMS-2 for Enhanced Oxidation of Hg0 at Ambient Temperature

Capturing mercury (Hg⁰) in raw natural gas is crucial for the stable operation of natural gas purification systems. However, achieving direct oxidation removal of Hg⁰ 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 Hg⁰ removal performance in simulated natural gas at ambient temperature. The sorbent achieved 97.0% Hg⁰ removal efficiency under a space velocity of 72 × 10⁴ 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 H₂S into polysulfide (S_n^2–) species. The accumulation of electrons around active S_n^2– groups accelerated electron transfer with Hg⁰ 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 Hg⁰.