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

Abstract

Transition-metal-mediated dinitrogen fixation has been intensively investigated. The employment of main group elements for this vital reaction has recently sparked interest because of new dinitrogen reaction chemistry. 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 multiple coordinatively unsaturated 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 far exceeds that of a catalytic process. The BaH₂ -mediated chemical looping process has prospects in future technologies for ammonia synthesis using transition-metal-free materials.

Keywords: Ammonia Synthesis; Barium Hydride; Chemical Looping; Nitrogen Fixation; Transition-Metal-Free.