A new high-efficiency nickel-based catalyst doped with rare earth metals for hydrogen production by ammonia decomposition

Abstract

The development of efficient and low-cost catalysts for hydrogen production via ammonia decomposition is crucial for the hydrogen economy. This work systematically investigates the promotional effects and underlying mechanisms of rare earth metals (La, Ce, Y) on Ni/γ-Al₂O₃ catalysts. A series of 8%Ni–M/γ-Al₂O₃ (M = La, Ce, Y) catalysts were synthesized via ultrasound-assisted impregnation. Comprehensive characterization (XRD, BET, SEM, XPS, EDS, NH₃-TPD) reveals that La doping optimally enhances Ni dispersion, increases surface oxygen vacancies concentration, and strengthens metal-support interaction. These synergistic modifications lead to superior catalytic performance. The 8%Ni–3%La₂O₃/γ-Al₂O₃ catalyst achieves ammonia conversion rates of 39.2%, 65.0%, 89.2%, and 98.8% at 500, 550, 600, and 700 °C, respectively, under a GHSV of 6000 mL g⁻¹ h⁻¹. This represents an activity enhancement of ∼11%, ∼20%, and ∼8% at 500, 550, and 700 °C, respectively, compared to the undoped catalyst. Most importantly, La doping significantly reduces the apparent activation energy to 66.8 kJ mol⁻¹, providing direct kinetic evidence for the facilitated reaction pathway. The promotional mechanism is attributed to La-induced oxygen vacancies which favor NH₃ activation and the improved Ni dispersion which provides more active sites. This study elucidates the structure-activity relationship in rare earth promoted Ni catalysts and offers a strategic guideline for designing high-performance, non-noble metal catalysts for sustainable hydrogen production.