Sm(II)-catalyzed reduction of dinitrogen, nitrite and nitrate to ammonia or urea

Industrial dinitrogen reduction to ammonia in the Haber-Bosch synthesis is essential for the production of fertilizers, and consequently, of food. This process accounts for up to 2% of global energy use. Methods wherein the energy for nitrogen activation is supplied by light could provide more sustainable alternatives to existing ones. The first transition-metal free molecular photocatalyst for the reduction of dinitrogen to ammonia is reported. The catalyst is based on Earth-abundant Sm. The reaction proceeds at ambient pressure and temperature with high turnover numbers (up to 70) with visible light irradiation in aqueous solvent mixtures and even pure water, and uses an environmentally benign non-metallic sacrificial reductant. Nitrite and nitrate were also efficiently reduced to ammonia. The first photocatalytic co-reduction of nitrite and bicarbonate to urea using a Sm-based photocatalyst was achieved.