Retrofitting Zr-Oxo Nodes of UiO-66 by Ru Single Atoms to Boost Methane Hydroxylation with Nearly Total Selectivity.

Direct selective oxidation of methane (DSOM) to high value-added oxygenates under mild conditions is attracting considerable interest. Although state-of-the-art supported metal catalysts can improve methane conversion, it is still challenging to avoid the deep oxidation of oxygenates. Here, we develop a highly efficient metal-organic frameworks (MOFs)-supported single-atom Ru catalyst (Ru/UiO-66) for the DSOM reaction using HO as an oxidant. It endows nearly 100% selectivity and an excellent turnover frequency of 185.4 h for the production of oxygenates. The yield of oxygenates is an order of magnitude higher than that on UiO-66 alone and several times higher than that on supported Ru nanoparticles or other conventional Ru catalysts, which show severe CO formation. Detailed characterizations and density functional theory calculations reveal a synergistic effect between the electron-deficient Ru site and the electron-rich Zr-oxo nodes of UiO-66 on Ru/UiO-66. The Ru site is responsible for the activation of CH via the resulting Ru═O* species, while the Zr-oxo nodes undertake the formation of oxygenic radical species to produce oxygenates. In particular, the Zr-oxo nodes retrofitted by Ru can prune the excess HO to inactive O more than OH species, helping to suppress the over-oxidation of oxygenates.