Subnanometric alkaline-earth oxide clusters for sustainable nitrate to ammonia photosynthesis.

The limitation of inert N2 molecules with their high dissociation energy has ignited research interests in probing other nitrogen-containing species for ammonia synthesis. Nitrate ions, as an alternative feedstock with high solubility and proton affinity, can be facilely dissociated for sustainable ammonia production. Here we report a nitrate to ammonia photosynthesis route (NO3-RR) catalyzed by subnanometric alkaline-earth oxide clusters. The catalyst exhibits a high ammonia photosynthesis rate of 11.97 mol gmetal-1 h-1 (89.79 mmol gcat-1 h-1) with nearly 100% selectivity. A total ammonia yield of 0.78 mmol within 72 h is achieved, which exhibits a significant advantage in the area of photocatalytic NO3-RR. The investigation of the molecular-level reaction mechanism reveals that the unique active interface between the subnanometric clusters and TiO2 substrate is beneficial for the nitrate activation and dissociation, contributing to efficient and selective nitrate reduction for ammonia production with low energy input. The practical application of NO3-RR route in simulated wastewater is developed, which demonstrates great potential for its industrial application. These findings are of general knowledge for the functional development of clusters-based catalysts and could open up a path in the exploitation of advanced ammonia synthesis routes with low energy consumption and carbon emission.