Dai, Bo; Li, Zichuang; Li, Wenqian; Li, Jiang; Lu, Xiaojun; Qian, Kailong; Jiang, Ruoqian; ... Ye, Tian-Nan; + view all Dai, Bo; Li, Zichuang; Li, Wenqian; Li, Jiang; Lu, Xiaojun; Qian, Kailong; Jiang, Ruoqian; Zou, Ying; Lu, Yangfan; Zhang, Qing; Qi, Yanpeng; Xu, Miao; Wang, Feng Ryan; Hosono, Hideo; Chen, Jie-Sheng; Ye, Tian-Nan; - view fewer (2025) Precise Vacancy Fitting of Horizontal Dinitrogen for Ammonia Synthesis. Journal of the American Chemical Society 10.1021/jacs.5c08337. (In press).

Text JACS NH3.pdf - Accepted Version Access restricted to UCL open access staff until 29 October 2026. Download (1MB)

Abstract

Efficient ammonia synthesis under mild conditions remains a significant challenge in modern chemistry. Chemical looping ammonia synthesis (CLAS) presents a sustainable alternative for ammonia production under near-ambient pressure conditions. In this study, we introduce a “horizontal N2” approach in the CLAS process, where an N2 molecule is horizontally incorporated into the surface lattice of the catalyst, facilitating effective N2 activation and subsequent NH3 production. Utilizing barium carbide (BaC2) as a model material, we show that the surface dianion vacancy sites of BaC2 provide optimal spacing for N2 activation, while the loaded Ni nanoparticles are responsible for H2 activation, enabling N2 hydrogenation from both ends to produce NH3 under mild conditions. Resonant inelastic X-ray scattering (RIXS) analysis combined with computational calculations reveals that the rate-determining step of the CLAS process is the hydrogenation of *HNNH, significantly lowering the activation energy required for N2 dissociation. The NH3 production rate for Ni/BaC2 is one order of magnitude higher than that reported for conventional CLAS catalysts and even surpasses the performance of the state-of-the-art 3d transition metal catalyst for catalytic ammonia synthesis at mild conditions of 100 °C and atmosphere. Unlike traditional CLAS catalysts, which typically suffer from deactivation, the dianion vacancy sites in Ni/BaC2 demonstrate exceptional catalytic stability, maintaining consistent activity over 20 h without noticeable degradation. These findings highlight the potential role of surface vacancy sites in CLAS reaction cycles and offer a new catalyst design concept for developing earth-abundant catalysts in ammonia synthesis.

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