Synergistic improvement of RuO2/CeO2 catalysts on Hg0 oxidation from SO2-containing flue gas: A theoretical and experimental study

Catalytic oxidation has been a promising technique for removing elemental mercury (Hg⁰) in coal-fired power plants. In this study, RuO₂ loaded CeO₂ nanorods (CeO₂-R) and CeO₂ nanoparticles (CeO₂-P) were prepared to investigate their Hg⁰ oxidation performance in SO₂-containing flue gas. Reaction mechanisms of Hg⁰ oxidation under different flue gas were evaluated through density functional theory calculations. The results show that CeO₂-R had a much higher Hg⁰ oxidation efficiency than that of CeO₂-P. The RuO₂ loaded CeO₂-R catalyst (RuO₂/CeO₂-R) exhibited superior Hg⁰ oxidation efficiency exceeding 90 % within the temperature range of 100–200 °C, with the maximum efficiency of 97.13 % at 200 °C. Meanwhile, the RuO₂/CeO₂-R catalyst displayed an enhanced sulfur resistance compared to the CeO₂-R catalyst, preserving 91.10 % oxidation efficiency with 500 ppm SO₂. Theoretical calculations indicate that active oxygen (O_a) was generated from molecular oxygen (O₂) at oxygen vacancies (O_v) on the CeO₂(110) surface, a process accelerated by the presence of HCl. Subsequently, the O_a promoted the activation of HCl on the RuO₂(110) surface, thereby facilitating the overall oxidation process of Hg⁰. Furthermore, the higher adsorption energy of SO₂ at the CeO₂(110) bridge sites, compared to the O_v sites of CeO₂(110)-O_v and the RuO₂(110) surface, suggests that the CeO₂(110) bridge sites can effectively prevent sulfur poisoning of the active sites on catalysts involved in Hg⁰ oxidation. This study reveals an improved synergistic effect of RuO₂/CeO₂ catalysts on Hg⁰ oxidation and sulfur resistance, providing potential application in the catalytic oxidation of elemental mercury from coal-fired flue gas.