Hydrogen production via ammonia decomposition is a crucial pathway toward achieving a "carbon-neutral society", and its catalytic efficiency is significantly influenced by the regulation of support materials. Based on the similar electronic structures of Al and Y elements, which belong to the main group and the subgroup (transition metal group) respectively, the differentiation mechanisms of Y?O? and Al?O? supports in cobalt-based catalysts were systematically compared.Catalyst characterization was performed using XRD, BET, SEM, XPS, H₂-TPR, and NH₃-TPD. The results show that although both Al and Y are trivalent, Y, as a rare-earth transition element, possesses a unique 4f electron configuration, which endows Y₂O₃ with richer oxygen vacancies and stronger electron-donating ability, significantly promoting the formation and dispersion of active Co²⁺ species. The 10Co/Y₂O₃ catalyst achieves an ammonia conversion of 100% at 700 ℃, and its specific surface area activity is 3.2 times that of 10Co/Al₂O₃. Although Al₂O₃ exhibits higher specific surface area and thermal stability, the spinel phase CoAl₂O₄ formed between the main-group element Al and Co shows low activity. This study provided new insights for the rational design of catalysts based on the periodic law.