Ni/MgO Catalysts for Ammonia Decomposition: Impact of Ni Loading, Reducibility, and Promoter Effects

Ammonia is emerging as a carbon‐free hydrogen carrier, making efficient catalysts for NH ₃ decomposition essential for clean energy applications. In this study, Ni/MgO nanocomposite catalysts with 5–50 wt% Ni were synthesized and evaluated for ammonia cracking. Structural characterization (XRF, PXRD, FE‐SEM, EDS mapping, TEM, HR‐TEM, SAED) revealed that increasing Ni loading promotes the transition from highly dispersed Ni species to larger, well‐connected, crystalline Ni nanoclusters with strong Ni/MgO interfacial interactions. H ₂ ‐TPR confirmed enhanced reducibility at higher Ni loadings. Catalytic activity strongly correlated with Ni domain continuity and reducibility, with 30% and 50% Ni/MgO achieving 90% NH ₃ conversion at 618°C and 605°C, respectively, at a GHSV of 20,400 mL/g _cat /h, achieving much higher activity than the catalysts with lower Ni content. Alkali promoters (Cs, K) offered only marginal improvement (598ºC). The 50% Ni/MgO catalyst also showed excellent stability, maintaining constant NH ₃ conversion for 72 h at 600°C. These results demonstrate a clear structure–reducibility–activity relationship and identify high‐Ni‐loaded Ni/MgO catalysts as promising, durable candidates for carbon‐free ammonia decomposition.