Hydrogen generation by ammonia decomposition over Co/CeO2 catalyst: Influence of support morphologies

Abstract

The fabrication of nanomaterial is a crucial issue in heterogeneous catalysis for on-site generation of hydrogen in proton exchange membrane fuel cell to achieve excellent performance for ammonia decomposition, and their effects of morphologies are still mysterious in the structure-reactivity relationship. In order to disclose it, three kinds of CeO2 supports with three-dimensionally ordered mesoporous structure (3DOM), nanotubes (NT) and nanocubes (NC) were synthesized by nanocasting of a mesoporous silica KIT-6 template with cubic Ia3d symmetries, hydrothermal method with and without urea, respectively. Various characterization methods (XRD, BET, H2-TPR, CO-TPD, TEM and XPS) were used to characterize the structure-reactivity relationship of catalysts. The Co/CeO2-3DOM catalyst had higher H2 producing rate (4.2 mmol/min･gcat) than Co/CeO2-NC (3.5 mmol/min･gcat) and Co/CeO2-NT (3.2 mmol/min･gcat) under the reaction conditions of 500 °C and GHSV = 6000 mL/gcat･h. The Co/CeO2-3DOM catalysts presented Co nanoparticles with mean size of 5.2 nm, and the highest surface Co concentration (5.12%) and Ce3+/Ce4+ ratio (0.53). Its high activity is attributed to higher surface area and more surface oxygen vacancies. The specific surface area and surface oxygen vacancy are significantly affected by the morphology of CeO2 support. The more mechanism insight of the structure-activity relationship for ammonia decomposition has been revealed.