Promoting N–H Bond Formation by an Alkali Metal Hydride under Confinement

The activation of dinitrogen is the key step in ammonia production, which is usually conducted at transition-metal catalysts (Fe and Ru) with the condition of high temperatures and pressures (400–500 °C and 10–30 MPa). A recent development in catalytic ammonia synthesis is the use of potassium hydride-intercalated graphite (K x H y C z ) as catalysts, which can activate dinitrogen at relatively moderate temperatures and pressures (250–400 °C and 1 MPa) without expensive transition metals. The nanoconfinement of alkali metal hydride between the graphene layers plays an important role in the activation and conversion of dinitrogen. It is attractive to further elucidate the interplay rules between nitrogen-based intermediates, metal hydride, and graphene layers. In this work, we designed three kinds of alkali metal hydride (MH)-intercalated graphene catalysts (Li x HC96, Na x HC96, K x HC96) as a platform for exploring the reaction mechanism of nitrogen at two-dimensional confinement. We found that the alternating associative pathway of the ammonia synthesis is dominant over the MH-intercalated graphene catalysts. The activated *H from MH contributes to the hydrogenation process of N2 to form NH3 molecules. The graphene layers with Å-level confined spacing promote the electron transfer between the reaction intermediate and alkali metals, which is favorable for the regeneration of the MHC96 catalytic system. This work provides theoretical insights into the design of alkali metal hydride-based catalysts for nitrogen activation.