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

摘要

Direct selective oxidation of methane (DSOM) to highvalue-addedoxygenates under mild conditions is attracting considerable interest.Although state-of-the-art supported metal catalysts can improve methaneconversion, it is still challenging to avoid the deep oxidation ofoxygenates. Here, we develop a highly efficient metal-organicframeworks (MOFs)-supported single-atom Ru catalyst (Ru-1/UiO-66) for the DSOM reaction using H2O2 asan oxidant. It endows nearly 100 selectivity and an excellent turnoverfrequency of 185.4 h(-1) for the production of oxygenates.The yield of oxygenates is an order of magnitude higher than thaton UiO-66 alone and several times higher than that on supported Runanoparticles or other conventional Ru-1 catalysts, whichshow severe CO2 formation. Detailed characterizations anddensity functional theory calculations reveal a synergistic effectbetween the electron-deficient Ru-1 site and the electron-richZr-oxo nodes of UiO-66 on Ru-1/UiO-66. The Ru-1 site is responsible for the activation of CH4 via theresulting Ru-1=O* species, while the Zr-oxo nodesundertake the formation of oxygenic radical species to produce oxygenates.In particular, the Zr-oxo nodes retrofitted by Ru-1 canprune the excess H2O2 to inactive O-2 more than (OH)-O-center dot species, helping to suppress theover-oxidation of oxygenates.