Highly selective oxidation of methane to acetic acid enabled by deficient UiO-66 under mild conditions

The direct conversion of methane (CH 4 ) into higher-value C2 products is essential for the green and efficient conversion of clean energy. However, this conversion process faces significant challenges due to the difficulty in activating methane's C–H bonds and the complexity of controlling C–C coupling reactions. Herein, we design and construct the unsaturated metal Zr 4+ site by introducing ligand defects in UiO-66 through treatment with trifluoroacetic acid (TFA), which enables the direct oxidation of methane to acetic acid using H 2 O 2 under mild conditions. Remarkably, a volcano-shaped correlation was observed between the degree of ligand defects in UiO-66 and acetic acid selectivity. Under optimal conditions (150 °C), the catalyst achieved an outstanding acetic acid selectivity of 84% with a high yield of 1691 μmol·g cat. –1 . Notably, the catalyst exhibited exceptional stability, maintaining its performance over at least five consecutive reaction cycles. Through TFA modulation, the d -band center of the Zr 3 d orbital in Zr 4+ sites exposed by UiO-66 shifts upward. This promotes the decomposition of H 2 O 2 , thereby facilitating the formation and stabilization of highly reactive Zr–OH species, which enhances the activation of C–H bonds in CH 4 . The resulting *CH 3 species is further oxidized by *OH species into *COOH species, which undergo stable C–C coupling at exposed Zr 4+ sites to produce acetic acid. This work provides novel insights into the design of highly efficient catalysts for the direct conversion of methane into C2 oxygenates compounds under mild conditions.