CeO2 immobilized on magnetic core-shell microparticles for one-pot synthesis of imines from benzyl alcohols and anilines: Support effects for activity and stability

Abstract

Four types of core-shell materials with magnetic Fe₃O₄ 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 Fe₃O₄@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.

Keywords: CeO(2); Core-shell microparticles; Imines synthesis; Magnetic catalyst; Support effect.