Continuous Flow Photocatalysis Boosting C─N Coupling for Sustainable High-Efficiency Formamide Synthesis.

The construction of C─N bonds from simple precursors under ambient conditions is a fundamental challenge in green chemistry, especially when it comes to avoiding energy-intensive protocols. Here, we present a continuous flow photocatalytic platform that enables the efficient coupling of C─N bonds between methanol and ammonia at ambient temperature and pressure. By synergistically engineering a Pd clusters-decorated TiO2 photocatalyst (1Pd/TiO2) and a mass transfer-enhanced gas-liquid-solid Taylor flow reactor, the system achieves a remarkable formamide productivity of 256.80 µmol h-1 (6.83-fold enhancement compared to batch reactors) with less than 10% decay in production rate over 50 h of continuous operation, which is remarkably superior to state-of-the-art photocatalytic systems for the synthesis of C─N compounds from C1 small molecules. Distinguishing from the conventional simultaneous bimolecular one-electron oxidation pathway, a mechanistic study has shown that the precisely tailored Pd clusters on TiO2 induce charge polarization to drive methanol dehydrogenation toward critical *CH2O intermediates, enabling direct nucleophilic NH3 attack for C─N bond formation, thereby circumventing thermodynamic/kinetic barriers inherent to asynchronous radical generation in prior systems. This work establishes a paradigm for the sustainable, efficient synthesis of formamide via photocatalytic C─N coupling by bridging nanoscale photocatalyst engineering with macroscopic reactor design.