The relationship of morphology and catalytic performance of CeO2 catalysts for reducing nitrobenzene to azoxybenzene under the base-free condition

A series of CeO2 catalysts with seven morphologies were synthesized and applied in reducing nitrobenzene to azoxybenzene under the base-free condition. The CeO2 with higher Ce3+ proportion exhibited significantly enhanced yield of azoxybenzene. With the highest surface Ce3+ proportion, the rod-CeO2 showed the best performance with 89.8% azoxybenzene yield. [Display omitted] 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.