Synergistic “Nitrogen Trap” and “Hydrogen Pump” Strategy for Spatially Decoupled Ammonia Decomposition
The development of efficient, ruthenium-free catalysts for low-temperature ammonia decomposition is crucial for using ammonia as a hydrogen carrier. Conventional catalysts are typically limited by inefficient ammonia adsorption and strong hydrogen inhibition, which restrict their overall activity. Herein, we report a spatially decoupled catalytic system that integrates an oxynitride shell and a metallic cobalt core (Co@BaAl2O4–xNδ). In this system, anion vacancies in the oxynitride shell function as “nitrogen traps” for highly efficient ammonia adsorption and N–H bond activation, while the metallic cobalt core acts as a “hydrogen pump” facilitating rapid hydrogen recombination and desorption. This deliberate separation of reaction steps breaks the scaling relations inherent to single-site catalysts. To the best of our knowledge, the optimized Co@BaAl2O4–xNδ achieves the highest ammonia conversion (∼94.5%) at 475 °C among non-ruthenium-based catalysts, with stability over 200 h of continuous operation. Evidence from kinetic studies, isotopic labeling, and in situ spectroscopy confirms this concurrent synergistic mechanism. This work highlights the potential of spatial decoupling in catalyst design and establishes a paradigm for creating high-performance catalysts.