Metal–organic framework–derived CeO2 catalyst supported by carboxyl–functionalized MXene for oxidative coupling of benzyl alcohol with aniline

Abstract

Direct oxidative coupling of alcohols and amines is a highly sought–after method for imine synthesis, and non–precious metal catalysts have been identified as essential components for their efficient production. Here, we report a CeO2 catalyst that is supported by carboxyl–functionalized MXene (CFMX). The catalyst, referred to as CeO2–C@CFMX–T (where T is the pyrolysis temperature), was prepared by high–temperature pyrolysis of a Ce–based metal–organic framework (MOF) and MXene composite (MOF@MXene) in a nitrogen flow environment. The MOF@MXene composite was synthesized by directly assembling Ce–MOF on the outer surface of MXene, which was pre–functionalized with terminal carboxylated aryl diazonium salts. The developed CeO2–C@CFMX–873 exhibited outstanding catalytic behavior in the oxidative coupling of benzyl alcohol and aniline, without the need for any basic additives. The catalyst achieved high benzyl alcohol conversion (98.9 %), desirable imine selectivity (97.7 %), good recyclability (5 cycles), and broad substrate tolerance (22 examples) under mild conditions (353 K, air atmosphere). It was found that the CFMX support improved the dispersion of CeO2 nanoparticles and alleviated the problem of CeO2 aggregation during pyrolysis. The remarkable activity of CeO2–C@CFMX–873 was attributed to reversible Ce3+/Ce4+ redox pairs, abundant oxygen vacancies, and an appropriate number of acid–base sites.