Retrofitting Zr-Oxo Nodes of UiO-66 by Ru Single Atoms to Boost Methane Hydroxylation with Nearly Total Selectivity
Geqian Fang, Fenfei Wei, Jian Lin, Yanliang Zhou, Li Sun, Xin Shang, Sen Lin, Xiaodong Wang
Abstract
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 1 /UiO-66) for the DSOM reaction using H 2 O 2 as an oxidant. It endows nearly 100% selectivity and an excellent turnover frequency of 185.4 h –1 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 1 catalysts, which show severe CO 2 formation. Detailed characterizations and density functional theory calculations reveal a synergistic effect between the electron-deficient Ru 1 site and the electron-rich Zr-oxo nodes of UiO-66 on Ru 1 /UiO-66. The Ru 1 site is responsible for the activation of CH 4 via the resulting Ru 1 ═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 1 can prune the excess H 2 O 2 to inactive O 2 more than • OH species, helping to suppress the over-oxidation of oxygenates.