Solid solution for catalytic ammonia synthesis from nitrogen and hydrogen gases at 50 °C

The lack of efficient catalysts for ammonia synthesis from N₂ and H₂ gases at the lower temperature of ca. 50 °C has been a problem not only for the Haber-Bosch process, but also for ammonia production toward zero CO₂ emissions. Here, we report a new approach for low temperature ammonia synthesis that uses a stable electron-donating heterogeneous catalyst, cubic CaFH, a solid solution of CaF₂ and CaH₂ formed at low temperatures. The catalyst produced ammonia from N₂ and H₂ gases at 50 °C with an extremely small activation energy of 20 kJ mol⁻¹, which is less than half that for conventional catalysts reported. The catalytic performance can be attributed to the weak ionic bonds between Ca²⁺ and H⁻ ions in the solid solution and the facile release of hydrogen atoms from H⁻ sites.