Enhancing the reactivity of vanadium-based nitrogen carriers via Ba modification for efficient chemical looping ammonia synthesis

Pristine transition metal nitrogen carriers (NCs) for chemical looping ammonia synthesis (CLAS) generally suffer from inherently low reactivity, and effective strategies to rationally modulate their performance remain scarce. Herein, we propose a novel approach to enhance the reactivity and ammonia synthesis performance of vanadium nitride (VN) NCs by loading alkaline earth metal barium (Ba) onto their surface. The introduction of Ba significantly promotes lattice nitrogen conversion and H 2 dissociation, thereby accelerating the overall ammonia synthesis process. Structural characterizations reveal that the doped Ba exists in the form of thermally stable BaO species uniformly dispersed within the VN NC matrix. The presence of BaO functions as an electron donor, generating abundant basic sites on the VN surface and increasing its surface electron density. This electronic modulation weakens the V ≡ N bond strength, facilitates the formation of nitrogen vacancies, and remarkably boosts the lattice nitrogen conversion rate from 2.77% to 21.85%. Meanwhile, the elevated surface electron density promotes electron transfer to the σ∗ antibonding orbital of H 2 , weakening the H-H bond and lowering the activation energy for H 2 dissociation. Consequently, H 2 molecules are more readily cleaved into adsorbed atomic hydrogen species on the VN surface, which further improves ammonia synthesis efficiency. The optimized Ba-VN NC achieves an ammonia synthesis rate of 450 μmol g −1 h −1 and enables ammonia production at a substantially lower operating temperature compared with pristine VN NC. Furthermore, the catalyst exhibits excellent stability over 15 consecutive cycles with no noticeable degradation in ammonia yield. This work provides a feasible strategy for regulating transition metal NCs, enriches the design principles for nitrogen carriers, and offers new insights into the development of high-efficiency materials for CLAS.