Hydrogen production from ammonia decomposition over Ni/CeO2 catalyst: Effect of CeO2 morphology

Abstract

Ammonia (NH3) decomposition to release COx-free hydrogen (H2) over non-noble catalysts has gained increasing attention. In this study, three nanostructured CeO2 with different morphologies, viz. rod (R), sphere (Sph), and spindle (Spi), were fabricated and served as supports for Ni/CeO2 catalyst. The CeO2 supports are different in particle sizes, specific surface area and porosity, resulting in the formation of Ni nanoparticles with distinguished sizes and dispersions. The surface properties of the Ni/CeO2 catalysts are not only distinct but also influential, affecting the adsorption and desorption of NH3, N2, and/or H2 molecules. The Ni/CeO2-R catalyst shows superior catalytic activity compared to the other two, owing to its smaller Ni crystallite size and larger BET surface area. The most abundant strong basic sites are observed for Ni/CeO2-Spi catalyst based on its exposed CeO2(110) planes, which facilitates the donation of electrons to the Ni particles, benefiting the associative desorption of N atoms. Thus, Ni/CeO2-Spi shows higher catalytic activity than Ni/CeO2-Sph, despite their almost identical Ni crystallite sizes.