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 COx‑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·gmetal−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. Confinement architectures are crucial for heterogeneous catalysis, yet existing methods for preparing encapsulated catalysts are often costly, complex, and unreliable. Here, the authors report a facile, template-free strategy that intercepts amorphous intermediates during solid-state reactions to generate encapsulation layers around active metals, providing a general blueprint for constructing durable confinement architectures in encapsulated metal catalysts.