Understanding Aerobic Nitrogen Photooxidation on Titania through In Situ Time-Resolved Spectroscopy

Nitrate is an important raw material for chemical fertilizers, but it is industrially manufactured in multiple steps at high temperature and pressure, urgently motivating the design of a green and sustainable strategy for nitrate production. We report the photosynthesis of nitrate from N₂ and O₂ on commercial TiO₂ in a flow reactor under ambient conditions. The TiO₂ photocatalyst offered a high nitrate yield of 1.85 μmol h^-1 as well as a solar-to-nitrate energy conversion efficiency up to 0.13 %. We combined reactivity and in situ Fourier transform infrared spectroscopy to elucidate the mechanism of nitrate formation and unveil the special role of O₂ in N≡N bond dissociation. The mechanistic insight into charge-involved N₂ oxidation was further demonstrated by in situ transient absorption spectroscopy and electron paramagnetic resonance. This work exhibits the mechanistic origin of N₂ photooxidation and initiates a potential method for triggering inert catalytic reactions.