Turn Waste into Treasure: Gas–Solid Photoreduction of NO in Flow for Separation-Free Ammonia Synthesis
Jianping Sheng, Ye He, Fengyi Zhong, Chenyu Du, Guijie Liang, Xiaodan Ma, Yanjuan Sun, Fan Dong
Abstract
Photo/electrocatalytic ammonia (NH 3 ) synthesis via nitrous oxide (NO x ) reduction is challenged by low NO solubility in electrolytes, inefficient electron and proton supply, and the high cost of separating NH 3 from dilute NH 4 + product solutions. In this study, we present a continuous, separation-free gas–solid photoreduction strategy for direct NH 3 gas production from flue gas, enabled by dynamic band structure regulation of the photocatalyst. Comprehensive in situ characterization and theoretical analysis demonstrate that this approach utilizes photoexcited oxygen vacancies (PV O ) in TiO 2 to generate high-energy electrons in deep conduction bands, thereby enhancing the reduction capacity, accelerating electron transfer, and lowering the activation energy for both H 2 O dissociation and NO hydrogenation. The real-time tracking of NO radicals in a gas–solid system using operando EPR provides crucial mechanistic insights into high-energy electron behavior and the NO-to-NH 3 conversion pathway, where these high-energy electrons not only promote efficient NO-to-NH 3 conversion but also prevent toxic N 2 O byproduct formation, ensuring selective and efficient reduction. The optimized TiO 2 –PV O catalyst achieves an NH 3 production rate of 79.86 ± 3.48 μmol g –1 h –1 with nearly 100% selectivity, a 16-fold improvement over pristine TiO 2 . This study offers valuable insights into solar-driven gas–solid NH 3 synthesis from flue NO x .