Metal-Free Photocatalytic CO Reduction to CH and H O under Non-sacrificial Ambient Conditions.

Photocatalytic CO reduction to CH requires photosensitizers and sacrificial agents to provide sufficient electrons and protons through metal-based photocatalysts, and the separation of CH from by-product O has poor applications. Herein, we successfully synthesize a metal-free photocatalyst of a novel electron-acceptor 4,5,9,10-pyrenetetrone (PT), to our best knowledge, this is the first time that metal-free catalyst achieves non-sacrificial photocatalytic CO to CH and easily separable H O . This photocatalyst offers CH product of 10.6 μmol ⋅ g  ⋅ h under non-sacrificial ambient conditions (room temperature, and only water), which is two orders of magnitude higher than that of the reported metal-free photocatalysts. Comprehensive in situ characterizations and calculations reveal a multi-step reaction mechanism, in which the long-lived oxygen-centered radical in the excited PT provides as a site for CO activation, resulting in a stabilized cyclic carbonate intermediate with a lower formation energy. This key intermediate is thermodynamically crucial for the subsequent reduction to CH product with the electronic selectivity of up to 90 %. The work provides fresh insights on the economic viability of photocatalytic CO reduction to easily separable CH in non-sacrificial and metal-free conditions.