Ce-promoted Ni-NiO small ensemble constrained in an MgO catalyst for efficient hydrogen production through NH₃ decomposition

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.