Boosting catalytic efficiency of nanostructured CuO-supported doped-CeO2 in oxidative coupling of benzyl amines to N-benzylidenebenzyl amines and benzimidazoles: impact of acidic and defect sites.

This study presents the rational synthesis of Cu-supported doped-CeO₂ catalysts designed for the oxidation of benzylamine, both in the absence and presence of 1,2-diaminobenzene. The catalysts were prepared using a two-step method and characterized by various techniques, including XRD, Raman spectroscopy, BET surface area analysis, NH₃-TPD, pyridine-FTIR, H₂-TPR, XPS, SEM, and TEM. Raman and XPS analyses confirmed the presence of oxygen vacancy sites, with CuO/CeO₂-ZrO₂ displaying the highest concentration of these sites. H₂-TPR revealed strong metal-support interactions, while NH₃-TPD indicated that CuO/CeO₂-ZrO₂ possessed the greatest number of acidic sites. The pyridine-FTIR results indicates both the acidic sites present on the catalyst surface. The Cu/CeZr sample exhibits the lowest I_u^////I_Total ratio (0.0567) compared to the Cu/Ce (0.0843) and Cu/CeSi (0.0672) samples, indicating a higher number of Ce³⁺ species or a greater number of oxygen defect sites in the sample. The catalyst demonstrated excellent performance in converting benzylamine to imines and was also highly effective in the synthesis of benzimidazole from benzylamine and 1,2-diaminobenzene, broadening its application potential. The superior catalytic activity is attributed to the abundant oxygen vacancies, redox properties, strong metal-support interactions, and acidic sites. Furthermore, the CuO/CeO₂-ZrO₂ catalyst maintained its efficiency over five consecutive cycles, exhibiting robustness, high functional group tolerance, and reduced reaction times, making it a promising system for diverse catalytic applications. [ABSTRACT FROM AUTHOR]