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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℃ 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.