In the early 20th century, the Haber-Bosch process was developed to synthesize NH₃ from N₂ and H₂. This innovation enabled humanity to avert food shortages following the industrial revolution by facilitating large-scale production of fertilizers. Today, NH₃ is indispensable not only as a fertilizer but also as an industrial raw material. However, once inert N₂ is converted to reactive NH₃, it can further transform into other reactive nitrogen species (Nr), such as NO₃⁻, NO₂⁻, NOₓ, and N₂O. Recent studies on planetary boundaries have highlighted that the excessive release of these Nrs into the environment contributes to issues like global warming, air pollution, water contamination, eutrophication, and biodiversity loss (K. Richardson et al. Sci. Adv. 2023, 9, eadh2458. W. Steffen et al. Science 2015, 347, 1259855. J. Rockström et al. Nature 2009, 461, 472). As the emphasis on carbon neutrality grows, achieving nitrogen neutrality has also become a pressing concern. Generally, microbial processes in sewage treatment facilities detoxify NO₃⁻ by converting it back to N₂ using hydrogen donors as reductants. Industrially, NO and NO₂ are detoxified using NH₃ as a reductant through selective catalytic reduction to form N₂. These methods, however, necessitate reconverting N₂ to NH₃ via the energy-intensive Haber-Bosch process for reuse. Therefore, directly converting NO₃⁻ to NH₃ without reverting to N₂ is highly desirable. Recent studies have reported direct conversion of NO₃⁻ to NH₃ using electron donors like formic acid and ethylene glycol, as well as electrochemical methods. However, these approaches often lack the incorporation of renewable resources or energy in NH₃ production from NO₃⁻. Recently, CH₄ has garnered attention as bio-CH₄ and e-CH₄, produced from biomass and methanation using green H₂ and CO₂, respectively. These forms of CH₄, closely associated with renewable resources and energy, are becoming increasingly available, though cost remains a challenge. In this context, we report a homogenous Re catalytic process that converts NO₃⁻ to NH₃ using CH₄, derived from renewable resources, as the reductant under UV light energy (T. Matsumoto et al. Angew. Chem. Int. Ed. 2025, e202423543).