CeO 2 immobilized on magnetic core-shell microparticles for one-pot synthesis of imines from benzyl alcohols and anilines: Support effects for activity and stability.

Four types of core-shell materials with magnetic Fe3 O4 microparticles as the core were prepared through different approaches using dopamine, glucose, tetrabutyl orthotitanate (TBOT), and tetraethyl orthosilicate (TEOS) as the shell precursor, respectively. CeO2 nanoparticles (NPs) was successfully immobilized onto these supports to fabricate efficient catalysts for the tandem catalytic synthesis of imines from benzyl alcohols and anilines at low temperature under air atmosphere. The as-prepared catalysts were detailedly characterized by TEM, EDX, XRD, FT-IR, XPS VSM, ICP, and CO2 -TPD. Interestingly, these prepared catalysts showed higher catalytic activity than reported CeO2 catalysts. Most attractively, the catalyst with a shell ofnitrogen-doped-carbon derived from dopamine exhibited the best catalytic property, and outstanding stability and recyclability in the cycle experiment. According to the XPS and CO2 -TPD characterization, the enhanced performance of Fe3 O4 @CN@CeO2 composites can be attributed to two reasons as follows: (1) the immobilization of CeO2 improved its alkalinity at low reaction temperature, and alkalinity is beneficial to promote the oxidation of alcohols to benzaldehyde, which is the rate-determining step for this tandem reaction; (2) the doped nitrogen generated Lewis basic site could satisfactorily stabilize Ce3+ /Ce4+ pair of CeO2 , which determined the catalytic activity and stability of CeO2 based catalysts for this tandem reaction. Moreover, the prepared catalysts could be facilely recovered from the reaction mixture with an external magnet. This work may provide a useful strategy for constructing CeO2 based catalysts for green and sustainable catalysis.