Fe2+-Triggered Unexpected Room Temperature H2S Catalytic Oxidation Activity in MIL-100(Fe)

The abundant Fe 3+ Lewis acidic sites and well-developed pore structure endow the Fe-MOFs with great potential for H 2 S catalytic oxidation at room temperature, but their performance is inferior owing to the insufficient redox ability of the Fe 3+ species inherent in frameworks. Herein, an effective protocol was proposed for the first time to remarkably improve the catalytic oxidation performance of MIL-100(Fe) under ambient conditions through the introduction of Fe 2+ coordinatively unsaturated site (CUS) species into the framework. As expected, the sample after modification had a superior H 2 S breakthrough capacity of 267.3 mg S/g, an 18.4-fold increase compared with that without Fe 2+ CUS (14.5 mg S/g). The introduced Fe 2+ species triggered the Fe 3+ /Fe 2+ redox cycle for H 2 S catalytic oxidation by enhancing the oxidative ability of the Fe 3+ CUS intrinsic to the framework. Moreover, the Fe 2+ CUS was also found act as an active site for O 2 activation into O 2 ∙– , which not only provides an additional pathway for H 2 S catalytic oxidation but also accelerates the redox cycling of Fe 3+ /Fe 2+ during the catalytic oxidation process. On the basis of the experimental findings, a plausible catalytic mechanism involving mixed-valence iron sites in MIL-100(Fe) was proposed.