Methane oxidation to ethanol by a molecular junction photocatalyst.

Methane, the major component of natural and shale gas, is a significant carbon source for chemical synthesis. The direct partial oxidation of methane to liquid oxygenates under mild conditions is an attractive pathway, but the molecule's inertness makes it challenging to achieve simultaneously high conversion and high selectivity towards a single target product. This difficulty is amplified when aiming for more valuable products that require C-C coupling. While selective partial methane oxidation processes have thus typically generated C oxygenates, recent reports have documented photocatalytic methane conversion to the C oxygenate ethanol with low conversions but good to high selectivities. Here, we show that the intramolecular junction photocatalyst CTF-1 with alternating benzene and triazine motifs drives methane coupling and oxidation to ethanol with a high selectivity and much improved conversion. The heterojunction architecture not only enables efficient and long-lived separation of charges after their generation, but also preferential adsorption of HO and O to the triazine and benzene units, respectively. This dual-site feature separates C-C coupling to form ethane intermediates from the sites where •OH radicals are formed and thereby avoids overoxidation. When loaded with Pt to boost performance further, the molecular heterojunction photocatalyst generates ethanol in a packed-bed flow reactor with improved conversion that results in an apparent quantum efficiency of 9.4%. We anticipate that further developing the "intramolecular junction" approach will deliver efficient and selective catalysts for C-C coupling, pertaining, but not limited, to methane conversion to C chemicals.