Preparation and ammonia decomposition performance of solid-solution-supported Ni-based catalysts

Abstract

The development of efficient and stable catalysts for ammonia decomposition is crucial for hydrogen production, addressing the challenges of hydrogen storage and transport. Nickel-based catalysts serve as promising alternatives to noble metals, yet they face challenges such as sintering and limited stability. This study focuses on the preparation and performance of Ce–Zr solid-solution-supported Ni-based catalysts to enhance their catalytic activity and durability. For comparison, a Y–Zr–O-supported catalyst was also prepared to elucidate the unique role of the Ce–Zr support. The Ni_2.5/Ce_xZr_1−xO₂ and Ni_2.5/Y_xZr_1−xO₂ catalysts were synthesized via the sol–gel method. XRD confirmed the formation of fluorite-structured Ce–Zr solid solutions (Ce_0.16Zr_0.84O₂, Ce_0.5Zr_0.5O₂, and Ce_0.6Zr_0.4O₂), while the Y–Zr system formed only a Y_0.18Zr_0.82O₂ phase due to its ionic radius mismatch. Characterization techniques including SEM, BET, XPS, H₂-TPR, and TPD revealed that the Ni/Ce_0.6Zr_0.4O₂ catalyst exhibited a high specific surface area (122.35 m² g⁻¹), abundant oxygen vacancies, excellent Ni dispersion, and optimal metal–support interaction. The Ni/Ce_0.6Zr_0.4O₂ catalyst achieved nearly 100% ammonia conversion at 550 °C under a gas hourly space velocity (GHSV) of 12 000 mL g_cat⁻¹ h⁻¹, significantly outperforming the catalysts supported on pure oxides or Y–Zr solid solutions. It also demonstrated high hydrogen production rates and exceptional stability over a 60-hour test with less than 5% activity loss. Its enhanced performance is attributed to the synergistic effects of the Ce–Zr solid solution, which improve the oxygen mobility, stabilize the structure, and facilitate NH₃ activation and N₂ desorption. This work demonstrates an effective strategy for designing non-noble metal catalysts with high efficiency and stability for the industrial decomposition of ammonia.