In situ XAFS Study of Ni/LaN catalysts for NH3 synthesis

Ammonia synthesis is constrained by the high barrier for N≡N activation, enforcing the harsh temperature and pressure conditions. The recently reported LaN emerged as a promising candidate, owing to its unique electride-like electronic structure and ability to stabilise nitrogen vacancies (VN). To elucidate the role of VN in N2 activation, we proposed to directly probe the LaN conduction band and La local coordination upon 1) VN formation, 2) adsorption and activation of N2. La L3, L2 and K edge XAFS experiments will be conducted under the H₂+N₂ mixtures between room temperature and 400 °C. The wide X-ray energy range between 4-90 keV at BM23 is ideal for this experiment. This study will clarify how VN electronically promote N₂ activation, differentiate between dangling and lattice-bound nitrogen species, and identify the key intermediates that control catalytic performance.

氨合成反应受限于N≡N三键活化的高能垒，因此需要严苛的温度与压强条件。近期报道的氮化镧（LaN）因其独特的类电子化物电子结构以及可稳定氮空位（VN）的特性，成为极具潜力的候选催化材料。为阐明氮空位（VN）在N₂活化过程中的作用，本研究拟直接探测氮化镧的导带以及镧的局域配位环境，具体涵盖两个场景：1）氮空位形成过程；2）N₂的吸附与活化过程。本研究将在氢气与氮气的混合气氛下，于室温至400℃的温度区间内开展镧的L3、L2及K吸收边X射线吸收精细结构谱（XAFS）实验。位于BM23光束线的4~90 keV宽X射线能量范围，完全适配本实验的需求。本研究将明确氮空位（VN）如何通过电子效应促进N₂活化，区分悬空氮物种与晶格结合氮物种，并鉴定出调控催化性能的关键反应中间体。