Zirconium-oxo Nodes of MOFs with Tunable Electronic Properties Provide Effective ⋅OH Species for Enhanced Methane Hydroxylation

Direct conversion of methane to high value-added oxygenates under mild conditions has attracted extensive interest. However, the over-oxidation of target products is usually unavoidable due to the easily excessive activation of C-H bond on the sites of supported metal species. Here, we identified the most efficient Zr-oxo nodes of UiO-66 metal-organic frameworks (MOFs) catalysts for the selective oxidation of methane with H₂ O₂ . These nodes were modified by three types of benzene 1, 4-dicarboxylates (NH₂ -BDC, H₂ BDC, and NO₂ -BDC). Detailed characterizations and DFT calculations revealed that these ligands can effectively tune the electronic properties of Zr-oxo nodes and the H₂ BDC ligand led to optimal electronic density of Zr-oxo nodes in UiO-66. Thus the UiO-66-H catalyst promoted the formation of ⋅OH species that adsorbed on Zr-oxo nodes, and facilitated the activation of methane with a lower energy barrier and subsequent conversion to hydroxylation oxygenates with 100 % selectivity.