Transition metal enhanced chromium nitride as composite nitrogen carrier for sustainable chemical looping ammonia synthesis

Chemical looping ammonia synthesis (CLAS) is promising to achieve decentralized ammonia synthesis under ambient pressure. Here, we develop a highly selective composite nitrogen carrier for efficient CLAS based on transition metals (TMs=Co, Ni, Fe) decorated chromium nitride (CrN). Systematic studies indicate that the pristine CrN is extremely inert: only 4.5% lattice nitrogen can be consumed in reacting with H2 (700 °C, 1 bar). Upon loading cobalt, the composite nitrogen carrier achieves lattice nitrogen conversion of 50.7% and ammonia selectivity up to 98.1%. Furthermore, Co-CrN exhibits excellent CLAS performance, attaining an average ammonia production rate of 466.1 μmol g−1 h−1 in 12 chemical loopings, which is ∼10 times that of the pristine CrN. Theoretical calculations reveal that the nitrogen vacancies generated in hydrogenation play a crucial role as activation centers for N2 fixation through a Mars–van Krevelen mechanism. This work provides a novel strategy to optimize nitrogen carriers for enhanced CLAS. [Display omitted] •CLAS mediated by Cr-based nitrogen carriers was reported for the first time.•Novel strategy in designing synergistic nitrogen carriers with dual active sites.•Controlled conversion rate of lattice-N by 50.7% and high NH3 selectivity at 98.1%.•Sustainable NH3 production rate achieved 466.1 μmol g−1 h−1 in more than 12 cycles.•Reduced reaction energy barrier was verified in DFT calculations.