Development of MgO-Al₂O₃ supported on single and bimetallic oxide catalysts for NH₃ decomposition to H₂ production

Ammonia (NH₃) decomposition is a promising route for carbon-free hydrogen (H₂) production; yet its industrial viability remains limited by the scarcity of low-cost, high-activity catalysts with long-term thermal stability. This study aimed to develop and optimize non-noble single-metal (CoO, FeO, ZnO) and bimetallic (CoFeO, CoZnO) oxide catalysts supported on MgO-Al₂O₃ for efficient NH₃ decomposition. The novelty of this work lies in the development of low-cost, non-noble metal catalysts that achieve high ammonia conversion efficiency and good thermal stability for NH₃ decomposition. The catalysts were synthesized through hydrothermal carbonization and comprehensively characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy with energy-dispersive X-ray analysis (FESEM-EDX), Brunauer-Emmett-Teller (BET) surface area measurements, thermogravimetric analysis (TGA), H₂ temperature-programmed reduction (H₂-TPR) and X-ray Photoelectron Spectroscopy (XPS). Among the single-metal catalysts, CoO/MgO-Al₂O₃ exhibited the highest NH₃ conversion (77.7% at 650 °C), prompting the design of cobalt-based bimetallic systems. While the CoFeO/MgO-Al₂O₃ catalyst achieved superior conversion (87.2% at 650 °C), attributed to synergistic Co-Fe electronic interactions that enhanced N-H bond cleavage kinetics. Kinetic studies revealed a high hydrogen yield of 92.4% at optimal conditions, further solidifying the catalyst’s potential. Structural and textural analyses confirmed the formation of mixed-oxide nanodomains, uniform metal dispersion, and mesoporosity retention favorable for active-site exposure. Using Response Surface Methodology (Box-Behnken design), process variables were statistically optimized, yielding a robust predictive model for maximum conversion. The recyclability studies further revealed sustained catalytic activity and stability over 9 cycles. Overall, CoFeO/MgO-Al₂O₃ emerges as a cost-effective, thermally durable, and high-performance non-noble catalyst for ammonia decomposition and hydrogen production advancing ammonia-to-hydrogen technology toward scalable green-energy applications.