Methane partial oxidation by monomeric Cu active center confined on ZIF-7

The monomeric cupric ion (Cu2+) species coordinated to four nitrogen ligands (CuN4) is recognized as a possible active site for particulate methane monooxygenase (pMMO) of the methanotrophic bacteria that convert methane to methanol. Herein, inspired by the active site of pMMO, a copper-doped zeolitic imidazolate framework-7 (Cu/ZIF-7) was prepared, the mononuclear CuN4 centers of which displayed catalytic partial oxidative activity and converted methane to methanol, methyl hydroperoxide, and hydroxymethyl hydroperoxide without producing the overoxidized product of formic acid. Spectroscopy studies established the mononuclear Cu2+ center coordinates with four benzimidazole nitrogens. The catalytic activity of Cu/ZIF-7 was scrutinized considering the potential reaction mechanism at the CuN4 center, which substantially reduced the strong acidity of ZIF-7 to afford the partial oxidation of methane without forming formic acid.