Promoted Multimetal Oxide Catalysts for the Generation of Hydrogen via Ammonia Decomposition

Mesoporous multimetal oxide microspheres (Ni-Ce-Al-O) with tuned and uniformly distributed composition are prepared through an aerosol-assisted self-assembly approach and further used as catalysts for ammonia decomposition. The as-prepared and spent materials are characterized by various techniques including ex situ/in situ X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), scanning electron microscope (SEM)/transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and N-2-adsorption. The tricomponent Ni-Ce-Al-catalysts show great superiority over pure NiO or bicomponent catalysts (Ni-Ce-O and Ni-Al-O) in both catalytic activity and durability. By using H-2-TPR combined with in situ XRD, we have identified metallic Ni-0 as the active crystalline phase and further confirmed the strong interaction between alumina and other components. This strong interaction helps suppress the growth of both metallic Ni-0 as active site and ceria as promoter under the harsh catalytic conditions (high temperature and reducing atmosphere) and thus improves the activity and stability simultaneously.