Nb2O5/Ce1–xNbxO2−δ Nanorod Catalyst for Selective Oxidative Coupling of Aromatic Alcohols and Amines

This study showed the dual role of Nb (dopant and active site) in improving the structure–activity properties of shape-controlled CeO2 nanorods for the selective synthesis of functional imines and benzimidazoles via oxidative coupling of benzyl alcohols with anilines and o-phenylenediamines, respectively. The powder X-ray diffraction (XRD) studies showed the lattice contraction of fluorite ceria due to the replacement of larger Ce4+ (0.97 Å) by smaller Nb5+ (0.74 Å) in the lattice, providing more defects (Ce3+ and oxygen vacancies), as elucidated by XPS studies. The dispersion of Nb2O5 on the surface of Nb-doped CeO2 nanorods provided strong acid sites, as confirmed by pyridine-adsorbed Fourier transform infrared (FT-IR) study. The combined effect of oxygen vacancies and acid sites could promote the activation of molecular oxygen and benzyl alcohol, respectively, achieving ∼97–99% yields of imine and benzimidazole in the liquid-phase C–N coupling reactions over the Nb-CeO2 nanorod catalyst calcined at 400 °C (NbCeNR4). The versatile catalytic efficiency of the NbCeNR4 nanomaterial is showcased by synthesizing various functional imines and benzimidazoles with good to excellent yields. The NbCeNR4 nanocatalyst is stable during the reaction as revealed by the hot filtration test and showed good catalytic reusability for 4 cycles.