Effects of low crystallinity cerium oxide on ammonia synthesis activity for cerium oxide supported ruthenium catalyst

Ruthenium (Ru) catalysts supported on cerium oxide (CeO2), which was composed of high crystallinity (HC) CeO2 covered by low crystallinity (LC) CeO2 were investigated. The ammonia synthesis activities of a series of Ru/CeO2(LC)/CeO2(HC), having different LC/HC ratios were evaluated, and various characterizations, such as N-2 adsorption, X-ray diffraction, hydrogen temperature-programmed reduction (H-2-TPR), and hydrogen temperature-programmed desorption (H-2-TPD), were performed. Ru/CeO2(LC)/CeO2(HC) (0.1) demonstrated higher activity. H-2-TPR revealed that H-2 consumption increased as the LC/HC ratio increased. This indicates that the larger the amount of low crystallinity CeO2, the higher the reducibility. However, the results of H-2-TPD imply that the larger the amount of low crystallinity CeO2, the higher the interaction between adsorbed H-2 and the catalyst surface. These results indicate that the balance of reducibility and hydrogen adsorption strength plays an important role in increasing the ammonia synthesis activity.