Systematic DFT Screening of Anti-Perovskite Nitrides for Chemical-Looping Ammonia Synthesis: Ca-Based Compounds as Promising Candidates

The sustainable synthesis of ammonia (NH3) under mild conditions requires advanced catalysts capable of efficiently activating the highly stable N≡N bond of molecular nitrogen (N2). Metal nitrides with chemical-looping functionality have recently emerged as promising candidates, in which lattice nitrogen vacancies (VN) serve as active sites for N2 activation. Among them, anti-perovskite nitrides (B3AN) are particularly attractive owing to their structural stability, yet only a few have been reported to exhibit chemical-looping capability. Herein, we performed a systematic density functional theory (DFT) screening of 35 experimentally reported B3AN compounds to evaluate their potential for vacancy-mediated N2 activation in chemical-looping NH3 synthesis. The DFT results revealed systematic trends in VN formation and N2 adsorption energetics associated with the electronegativity of the B-site element, χ(B), establishing χ(B) as a useful descriptor. Among the investigated materials, Ca-based B3AN compounds were identified as a promising candidate family with a favorable balance between VN formation and N2 adsorption energetics. These Ca-based compounds offer a materials platform for further exploration of anti-perovskite nitrides in chemical-looping NH3 synthesis.