Promoting the efficiency and selectivity of NO ₃ ⁻ −to−NH ₃ reduction on Cu−O−Ti active sites via preferential glycol oxidation with holes

Abstract

The combined reductive and oxidative reaction is the essence of a solar-driven photoredox system. Unfortunately, most of these efforts focus on the specific half-reactions, and the key roles of complete photoredox reactions have been overlooked. Taking the nitrate reduction reaction (NO 3 − RR) as a typical multiple-electrons involved process, the selective reduction of the NO 3 − into ammonia (NH 3 ) synthesis with high efficiency is still a grand challenge. Herein, a rational oxidative half-reaction is tailored to achieve the selective conversion of NO 3 − to NH 3 on Cu−O−Ti active sites. Through the coupled NO 3 − RR with glycol oxidation reaction system, a superior NH 3 photosynthesis rate of 16.04 ± 0.40 mmol g cat −1 h −1 with NO 3 − conversion ratio of 100% and almost 100% of NH 3 selectivity is reached on Cu−O−Ti bimetallic oxide cluster−anchored TiO 2 nanosheets (CuO x @TNS) catalyst. A combination of comprehensive in situ characterizations and theoretical calculations reveals the molecular mechanism of the synergistic interaction between NO 3 − RR and glycol oxidation pair on CuOx@TNS. The introduction of glycol accelerates the h + consumption for the formation of alkoxy (•R) radicals to avoid the production of •OH radicals. The construction of Cu−O−Ti sites facilitates the preferential oxidation of glycol with h + and enhances the production of e − to participate in NO 3 − RR. The efficiency and selectivity of NO 3 − −to−NH 3 synthesis are thus highly promoted on Cu−O−Ti active sites with the accelerated glycol oxidative half-reaction. This work upgrades the conventional half photocatalysis into a complete photoredox system, demonstrating the tremendous potential for the precise regulation of reaction pathway and product selectivity.