Promoting Mechanisms of Sulfation on Ir/TiO₂-S Catalysts in Methane Combustion

Developing iridium (Ir) catalysts with stable active Ir^δ+ species is critically important for low-temperature methane combustion. Sulfation modification of the support is effective in regulating the surface chemical environment of active metals via synergistic interaction of sulfates. Herein, a series of Ir/TiO₂ catalysts with varying sulfate (SO₄^2-) contents were successfully synthesized and evaluated for methane combustion. Among these, the Ir/TiO₂-4.1S catalysts exhibit superior methane combustion activity and thermal stability, achieving a turnover frequency of 10.3 × 10^-3 s^-1 at 225 °C─5.4 and 17.2 times higher than pristine Ir/TiO₂ (1.9 × 10^-3 s^-1) and excessively sulfated Ir/TiO₂-6.7S (0.6 × 10^-3 s^-1) catalysts, respectively. Detailed characterizations and theoretical calculations reveal that moderate sulfation of TiO₂ supports promotes the formation of active Ir^δ+ species and abundant oxygen vacancies. In situ DRIFTS results further demonstrate that the Ir-TiO₂-SO₄^2- synergy effectively stabilizes highly reactive Ir^δ+ species under methane combustion conditions. This synergistic effect significantly enhances CH₄ and O₂ adsorption and activation while lowering the dissociation energy of the initial C-H bond in methane, leading to markedly improved methane combustion efficiency. This work deepens the fundamental understanding of the Ir-TiO₂-SO₄^2- synergistic interaction in efficient methane combustion, providing valuable guidance for the design of advanced catalysts for low-temperature methane combustion.