The relationship of morphology and catalytic performance of CeO_2 catalysts for reducing nitrobenzene to azoxybenzene under the base-free condition

CeO₂ morphology was proposed to be a crucial factor for reducing nitrobenzene to azoxybenzene under the base-free condition. Herein, the structure-activity relationship of CeO₂ catalysts was explored to improve the azoxybenzene yield. A series of CeO₂ catalysts were synthesized with seven morphologies to obtain different Ce³⁺ proportion and various surface areas. Notably, the catalytic performance of these samples for reducing nitrobenzene to azoxybenzene enhanced with the increasing Ce³⁺ proportion. With the highest surface Ce³⁺ proportion, the Rod-CeO₂ catalyst exhibited 100% conversion of nitrobenzene and 89.8% azoxybenzene selectivity in 7 h at 150 °C under 1 MPa CO. Moreover, the preliminary mechanistic analysis indicated that the inhabitation of azoxybenzene to by-product azobenzene resulted in the high selectivity of azoxybenzene.