Efficient catalysts of surface hydrophobic Cu-BTC with coordinatively unsaturated Cu(I) sites for the direct oxidation of methane

Abstract

Selective oxidation of methane to organic oxygenates over metal–organic frameworks (MOFs) catalysts at low temperature is a challenging topic in the field of C1 chemistry because of the inferior stability of MOFs. Modifying the surface of Cu-BTC via hydrophobic polydimethylsiloxane (PDMS) at 235 ◦C under vacuum not only can dramatically improve its catalytic cycle stability in a liquid phase but also generate coordinatively unsaturated Cu(I) sites, which significantly enhances the catalytic activity of Cu-BTC catalyst. The results of spectroscopy characterizations and theoretical calculation proved that the coordinatively unsaturated Cu(I) sites made H2O2 dissociative into •OH, which formed Cu(II)-O active species by combining with coordinatively unsaturated Cu(I) sites for activating the C−H bond of methane. The high productivity of C1 oxygenates (CH3OH and CH3OOH) of 10.67 mmol gcat.−1h−1 with super high selectivity of 99.6% to C1 oxygenates was achieved over Cu-BTC-P-235 catalyst, and the catalyst possessed excellent reusability.