Photosynthesis of NH3 from NO3– using CH4 in Homogenous Re Catalysis at Room Temperature and Normal Pressure

We present rhenium (Re) catalysis of one-pot synthesis of ammonia (NH3) from nitrate (NO3–) using methane (CH4) as a reductant under ultraviolet (UV) light irradiation at room temperature and normal pressure. Currently, a large amount of NH3 is synthesized through nitrogen fixation by artificial methods in addition to natural synthesis. The amount of NH3 from the artificial Haber-Bosch process using hydrogen (H2) and nitrogen (N2) gases increases in industrial process, which causes the increases of amount of reactive nitrogen containing NO3– on the earth. NO3– leads to environmental issues such as water contamination, eutrophication and biodiversity loss. In a natural system and a sewage facility, NO3– can be detoxified to N2 using a hydrogen donor by microbial process. However, it is better to convert NO3– to NH3 rather than N2 since N2 must be converted back to NH3 by the energy-intensive Haber-Bosch process. To develop a desirable process of NO3– to NH3 for a sustainable society, it is required that the reducing agent is derived from a renewable resource/energy. Thus, we turned our attention to CH4, which has high affinity with renewable resource/energy since it is produced from livestock waste. Therefore, our system reported here is to directly convert NO3– to NH3 using CH4 with light energy without going through the Haber-Bosch process. To the best of our knowledge, this is the first time of NH3 synthesis from NO3– using CH4 as a reductant.