Alkali and alkaline earth metal-promoted Ni/LaMnO₃ perovskite catalysts for efficient ammonia decomposition

Ammonia decomposition represents a promising pathway for carbon-free hydrogen production, contingent on the development of cost-effective and high-performance catalysts. In this study, LaMnO₃ was synthesized via a sol-gel method and employed as a perovskite support for Ni-based catalysts. A series of alkali and alkaline earth metal promoters (K, Cs, Sr, Ca, In) were incorporated to investigate their impact on catalytic activity and physicochemical properties. Structural and surface analyses (XRD, SEM-EDS, TEM, BET, XRF, H₂-TPR, and CO₂-TPD) confirmed the successful integration of promoter elements without compromising the perovskite structure. Catalytic testing revealed that unpromoted Ni/LaMnO₃ achieved 90% ammonia conversion only at 640 °C, highlighting the need for further enhancement. Among all samples, the 3%K–Ni/LaMnO₃ catalyst demonstrated superior performance, achieving 90% conversion at 530 °C and complete decomposition at 630 °C. K promotion significantly increased the surface area and porosity, enhanced the reducibility of Ni species, and improved surface basicity. Optimization of K loading revealed that 3 wt% was ideal, with higher concentrations leading to a slight decline in performance. Long-term stability evaluation at 600 °C for 24 h confirmed sustained catalytic activity and structural integrity. The observed catalytic activity followed the trend: 3%K–Ni/LaMnO₃ > 3%Cs–Ni/LaMnO₃ > 3%Sr–Ni/LaMnO₃ > 3%In–Ni/LaMnO₃ > 3%Ca–Ni/LaMnO₃ > Ni/LaMnO₃, and these results elucidate the critical role of potassium in enhancing the performance of Ni/LaMnO₃ catalysts, offering a practical route toward efficient hydrogen generation from ammonia.