Boosting SO2‑tolerant oxidation of Hg0 and chlorobenzene over MnCo2O4@TiO2 catalyst via constructing shielding effects

Abstract

Currently, it was still challenging to improve the SO₂-tolerant catalytic oxidation of Hg⁰ and chlorobenzene in flue gas. Herein, we developed a MnCo₂O₄@TiO₂ core-shell material that employed a self-shielding mechanism to prevent sulfate deposition. The optimal MnCo₂O₄@TiO₂-2 catalyst achieved 100% Hg⁰ removal efficiency at 250 °C under 150-600 ppm SO₂, and also showed enhanced SO₂ resistance during chlorobenzene conversion at 275 °C. The strong interaction between MnCo₂O₄ and TiO₂ facilitated the electronic transfer from MnCo₂O₄ to TiO₂, thereby producing more Co³⁺ and maintaining the high reactivity. Further, the mesoporous TiO₂ layer facilitated the generation of moderate acid sites, improved the distribution of surface oxygen species, and weakened SO₂ adsorption on catalyst. Under the protection of mesoporous TiO₂ layer, the generation of Mn/Co sulfates could be inhibited effectively. In particular, the suitable TiO₂ shell balanced the chemical adsorption and oxidation processes of Hg⁰ on the catalyst. This enhancement led to improved single Hg⁰ removal efficiency and SO₂-tolerant Hg⁰ removal performance. During chlorobenzene degradation in presence of SO₂, the oxidation path of chlorobenzene on MnCo₂O₄@TiO₂ occurred via chlorobenzene→ phenolates→ maleates→ formates/acetates→ CO₂ and H₂O. Although sulfate formation would cover the active surface and inhibit the reaction path, the TiO₂ shell could attenuate this negative effect. This study provided a new approach for the development of SO₂-tolerant transition metal oxide with superior performance, holding significant academic and practical value.