Transition-Metal-Free Barium Hydride Mediates Dinitrogen Fixation and Ammonia Synthesis

Transition-metal-mediated dinitrogen fixation has been intensively investigated. The employment of main group elements for this vital reaction recently aroused increasing interest because of new dinitrogen reaction chemistry. Herein, we report ammonia synthesis via a chemical looping process mediated by a transition-metal-free barium hydride (BaH₂). Experimental and computational studies reveal that the introduction of hydrogen vacancies is essential for creating coordinatively unsaturated multi-Ba sites for N₂ activation. The adjacent lattice hydridic hydrogen (H‾) then undergoes both reductive elimination and reductive protonation to convert N₂ to NH_x . The ammonia production rate supports this hydride-vacancy mechanism via a chemical looping route that is far exceeding that of a catalytic process. The BaH₂-mediated chemical looping process has prospects for the future development toward ammonia synthesis using transition-metal-free materials.