A Highly Stable and Active CaO/Al2O3 Base Catalyst in the Form of Calcium Aluminate Phase for Oxidation of Cyclohexanone to ε-Caprolactone

Abstract A series of CaO/Al 2 O 3 base catalysts with different crystal phases is prepared via thermal treatment. The as-prepared base catalysts are tested through Baeyer–Villiger oxidation of cyclohexanone to ε-caprolactone in liquid-phase using a mixture of aqueous hydrogen peroxide and benzonitrile as oxidant. The corresponding results show that the CaO/Al 2 O 3 catalysts with high thermal treatment temperature (e.g. 900 °C) exhibit excellent activity as well as stability. Upon these, the catalysts are characterized by TG–DTG, XRD, N 2 -physisorption, SEM and CO 2 -TPD techniques. The characterization results clearly suggest that such a stable and efficient catalytic performance is beneficial from the formation of calcium aluminate phase, thus overcoming one of base catalyst application barriers, that Ca or CaO species loss (leach) from CaO-based catalysts during reactions. Correspondingly, it can be inferred that the treatment of the catalysts at different temperatures results in the diverse distribution of basic strength. Furthermore, it is also demonstrated that the suitable base strength (medium strength is good for the reaction selected in the work) plays a critically role in the improvement of catalytic performance. Finally, the effects of operation conditions on catalytic activity and product selectivity are also determined and discussed. Graphical Abstract