Oxygen-Vacancy-Engineered Ru/Sr-Doped CeO ₂ Catalysts Enable Accelerated N–H Cleavage and N–N Recombination for Ammonia Decomposition

Ammonia is a promising vector for hydrogen storage and transport; however, its catalytic decomposition is often limited by the kinetic trade-off between N-H bond cleavage and N-N recombination. Herein, we report a Ru/Sr-doped CeO₂ catalyst in which aliovalent Sr²⁺ substitution for Ce⁴⁺ induces abundant oxygen vacancies (O_v). The optimized Ru/Sr_0.1Ce_0.9O_2-δ exhibits higher NH₃ conversion at 450 °C, delivering a hydrogen production rate of 2713 mmolg_Ru^-1 min^-1 (45% higher than pristine Ru/CeO₂), outperforming most reported Ru-based systems. Combined characterization and DFT calculations revealed that Sr doping introduced lattice charge imbalance, lowering the energy barrier for oxygen vacancies (O_v) formation. The increased vacancy concentration alters the local electronic structure and enhances electron transfer to Ru. Together, these effects modulate NH₃ adsorption and activation while facilitating N-N recombination. Furthermore, the defective support promotes hydrogen spillover from Ru to the support, effectively mitigating hydrogen poisoning and ensuring remarkable stability under realistic conditions. This study demonstrates that vacancy engineering via aliovalent doping establishes favorable electronic and hydrogen spillover characteristics, thereby enabling efficient and durable NH₃-to-H₂ conversion.