Synergistic modulation of oxygen vacancies and confinement effects in CeO₂ for high-selectivity synthesis of azoxyarenes

The selective reduction of nitrobenzene is considered the primary route for synthesizing azoxybenzene, yet this process often suffers from over-reduction, resulting in low selectivity toward the target product. Achieving efficient N–N coupling of key intermediates thus remains a central challenge for improving selectivity. To address this, we prepared a series of oxygen-vacancy-rich CeO₂ nanosphere catalysts by modulating acetic acid concentration and temperature during hydrothermal synthesis. These catalysts exhibit high specific surface areas (up to 184.1 m²·g⁻¹) and demonstrate excellent performance in the highly selective reduction of nitrobenzene to azoxybenzene. Mechanistic studies reveal that oxygen vacancies on the CeO₂ surface promote the condensation of nitrosobenzene and phenylhydroxylamine into azoxybenzene via a confinement effect. Moreover, X-ray photoelectron spectroscopy (XPS) analysis shows that azoxybenzene adsorbs much more weakly on the catalyst surface than nitrobenzene or aniline, favoring its rapid desorption and thereby suppressing further reduction. This work clarifies how oxygen vacancies in confined microenvironments on CeO₂ enhance the N–N coupling pathway, providing important theoretical and experimental guidance for designing highly selective catalytic systems for nitroarene reduction.