Visible-light-driven aerobic oxidation of HCl to Cl2 at room temperature

Abstract

The oxidative conversion of hydrogen chloride (HCl) to chlorine (Cl₂) is a pivotal reaction for valorizing industrial by-product HCl in a sustainable manner. Traditional approaches, such as the Kel-Chlor and Deacon processes, suffer from several limitations including high energy demands, reliance on corrosive sulfuric acid, and catalyst deactivation under impure conditions. Herein, we report a sulfuric acid-free, ambient-temperature strategy for HCl oxidation driven solely by visible light. This metal-free process employs sodium nitrite (NaNO₂) as a catalyst and achieves exceptional performance using either LED-based visible light or natural sunlight as the sole energy input. Under optimized conditions, the system achieves complete (100%) conversion of atmospheric oxygen to Cl₂, and over 80% conversion of HCl to Cl₂ using visible-light LED illumination. Notably, solar-driven operation also enables quantitative oxygen-to-chlorine conversion without any external heating or dehydration pretreatment. The process reaches energy conversion efficiency over 190 mol_Cl2 kWh⁻¹, underscoring its potential as a scalable, energy-efficient, and environmentally benign alternative to conventional HCl oxidation technologies. These findings establish a new paradigm in chlorine recovery by demonstrating the feasibility of a visible-light-driven, sulfuric acid-free Kel-Chlor variant, offering significant implications for green chemistry, industrial process intensification, and decentralized chlorine production.