Enhanced catalytic activity on the naphthalene hydrogenation reaction over Pt-Pd/Al₂O₃-CeO₂ catalysts

Alumina (Al₂O₃) and Alumina-Ceria (Al₂O₃-CeO₂) supports with different CeO₂ loadings (0, 2, 5, 10 and 50 wt.%) were prepared by the sol-gel method and impregnated with 0.5% of Pt and 0.5% of Pd (wt.%). The catalysts were characterized by Xray diffraction (XRD), Raman spectroscopy, UV-Vis diffuse reflectance spectroscopy (DRS), and scanning electron microscopy (SEM). The present work aims to study the influence of the ceria content over the catalytic activity of Pt-Pd/Al₂O₃-CeO₂ samples during the naphthalene hydrogenation reaction. The results show that as the cerium oxide content increases, the intensity of the diffraction peaks corresponding to this oxide also increases due to the high crystallinity of the ceria as compared to the polycrystalline alumina. At low CeO₂ contents, a shift of the peaks towards lower angles is observed, suggesting an incorporation of Al₂O₃ into the CeO₂ lattice. Similarly, Raman analyzes show a single band around 440 cm^-1 attributed to the formation of ceria, whose characteristic peak has been observed at approximately 459 cm^-1. This shift towards smaller energies is another indication of the incorporation of alumina in the ceria lattice. Finally, the aggregation of the ceria in the support also results in a decrease in the BET area of these materials. This enhancement in the catalytic performance was related to a supplementary contribution from naphthalene adsorbed on acidic sites on the support and reacting with hydrogen migrating from platinum and palladium surface by a spillover effect. The activity in the naphthalene hydrogenation showed a significant influence on the interaction between the metals (Pt, Pd) and the support (Al₂O₃-CeO₂).