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.

Photocatalysis utilizes sunlight as a sustainable energy source, offering an eco-friendly method for chemical synthesis and energy conversion. BiOX photocatalysts have gained significant attention due to their low toxicity, ease of preparation, and excellent photocatalytic performance. In this study, the BiOX nanosheets featuring with rich oxygen vacancies (OVs) were employed in the efficient photocatalytic C–S coupling reaction of aromatic alkynes and sulfonyl hydrazides, without external bases or additives. Compared to BiOCl and BiOBr, BiOI demonstrated superior catalytic activity for these reactions. Control experiments highlighted that the presence of trace amounts of water in the reaction system enhanced the reaction efficiency. OVs played a crucial role by exposing Bi metal atoms, facilitating water adsorption and dissociation, thereby enhancing hydroxyl radical generation and improving catalytic activity of BiOI. This novel synthesis approach of alkynyl sulfone not only broadens the application potential of semiconductor photocatalysts but also establishes a new green method for the photocatalytic synthesis of aryl acetylene sulfone compounds.