Ammonia is recognized for its potential in hydrogen storage and transportation. Among methods for hydrogen production from ammonia, catalytic decomposition stands out, and developing economical alternatives to noble metal catalysts like ruthenium (Ru) is crucial. Here, we report an exsolution strategy to obtain a size-constrained Ni⁰-NiO small ensemble on MgO that outperforms bare Ni single atoms and particles in ammonia decomposition. Adding Ce to the NiMg catalyst significantly enhances activity, doubling the hydrogen production rate to 92 mmol_H2 g_cat⁻¹ min⁻¹ at 550°C, surpassing most Ni-based catalysts. Characterization reveals the role of cerium in forming active Ni⁰-NiO ensembles by occupying specific sites on MgO. Cerium (Ce) also affects hydrogen and ammonia adsorption and alters reaction pathways. Our work highlights the structure control of transition metal sites and the promotion mechanism of rare-earth elements for ammonia conversion and hydrogen production reaction.

氨因其在氢储存和运输方面的潜力而受到认可。在氨制氢方法中，催化分解最为突出，开发钌 (Ru) 等贵金属催化剂的经济替代品至关重要。在这里，我们报告了一种外解策略，以在 MgO 上获得尺寸受限的 Ni ⁰ -NiO 小系综，其在氨分解中的性能优于裸露的 Ni 单原子和颗粒。在NiMg催化剂中添加Ce可显着提高活性，在550°C下将氢气产率翻倍至92 mmol _H2 g _cat ^-1 min ^-1，超过大多数镍基催化剂。表征揭示了铈通过占据 MgO 上的特定位点在形成活性 Ni ⁰ -NiO 系综中的作用。铈 (Ce) 还会影响氢和氨的吸附并改变反应途径。我们的工作重点关注过渡金属位点的结构控制以及稀土元素对氨转化和制氢反应的促进机制。