Amorphous BaO-Al₂O₃ encapsulation enables durable metal catalysts for ammonia decomposition

Confinement architectures stabilise active metal nanoparticles while preserving molecular accessibility, which proves crucial for heterogeneous catalysis. However, existing methods for preparing encapsulated catalysts such as mesoporous oxides, zeolites, and metal-organic frameworks are costly, complex, and often unreliable. Solid‑state reactions offer a promising alternative, yet conventional pathways yield thermodynamically stable phases that limit activity. Here, we propose a facile, template-free strategy that intercepts amorphous intermediates during solid‑state reactions to form encapsulation layers for active metals. We select ammonia decomposition reaction (ADR, 2NH₃ → N₂ + 3H₂) as the target catalytic reaction, which is a pivotal route to CO_x‑free hydrogen and affords the high‑temperature, reducing environment that drives solid‑state transformations. During ADR conditions, commercial BaCO₃ and Al₂O₃ act as solid‑state reactants, forming Al₂O₃-BaO encapsulation layers around Co or Ni nanoparticles. The layers effectively restrict nanoparticle growth. Amorphous Al₂O₃ facilitates NH₃ adsorption, and amorphous BaO accelerates N₂/H₂ release and enables N-H activation. As a result, the encapsulated catalyst delivers an intrinsic rate of 1,358 mmol H₂·g_metal^-1·min^-1 that surpasses existing non‑noble metal catalysts, alongside excellent durability during 480 h. This approach offers a blueprint for constructing durable confinement architectures in encapsulated metal catalysts.