Co-SiO₂ Nanocomposite Catalysts for CO_x -Free Hydrogen Production by Ammonia Decomposition

High-surface-area Co-SiO₂ nanocomposites were synthesized by a simple two-step procedure with activated carbon as the template. These materials catalyze the decomposition of ammonia to produce CO_x -free hydrogen. The fresh and used catalysts were characterized by various techniques including X-ray diffraction, N₂ adsorption-desorption, and transmission electron microscopy. Furthermore, temperature-programmed reduction by hydrogen combined with the corresponding in situ XRD analysis was performed to investigate the redox properties of the as-prepared catalysts. The strong interaction between the cobalt species and silica can effectively prevent the active cobalt nanoparticles from agglomerating during calcination and the ammonia decomposition reaction. The ammonia reaction rate reached about 7000 mol NH₃ mol_Co ^-1  h^-1 with a very high GHSV of 124 000 cm³  g_cat ^-1  h^-1 at 600 °C; this rate was maintained for 48 h without any observable deactivation of the as-obtained Co-SiO₂ nanocomposite catalyst.