Cu–N coordination-mediated H2S absorption and controlled oxidation for efficient wet oxidative desulfurization

Abstract

Conventional wet oxidative desulfurization suffers from the synchronous absorption–oxidation of H₂S, which induces sulfur deposition, viscosity rise, and equipment fouling. Here, we establish a stepwise “coordination capture-air regeneration” paradigm to achieve the absorption and controlled oxidation of H₂S. In this system, a Cu²⁺–1-MI (1-methylimidazole)/DMF (N,N-dimethylformamide) solvent system selectively anchors H₂S through Cu–N coordination during absorption, while controlled air exposure regenerates the solvent and precipitates sulfur in a separate stage. The formulation achieves a breakthrough capacity of 14.3 g L⁻¹ under ambient conditions, maintains ∼95% capacity after multiple absorb–regenerate cycles, and shows good water tolerance. At the optimal Cu²⁺ : 1-MI ratio of 1 : 2, the liquid is near-neutral (pH ≈ 7.3) and induces relatively low corrosion 304L/316L stainless steels. The combination of experiments, characterization studies and density functional theory (DFT) calculations indicate that the Cu–N center captures and stores HS⁻ through coordination mechanisms, and achieves mild oxidation of HS⁻ by activating oxygen, while itself recovering. During absorption operated without external O₂ co-feeding, a small fraction of S–O species is detected, consistent with limited side oxidation attributable to dissolved oxygen. Overall, this “coordination anchoring–selective regeneration” concept mitigates rapid solid accumulation and suppresses over-oxidation of sulfur products, offering a promising basis for practical wellhead and high-pressure natural-gas purification.