The catalytic Baeyer–Villiger oxidation of cyclohexanone to ε-caprolactone over cerium–tin oxide

Polycaprolactone synthesized via the ring-opening polymerization of ε-caprolactone assumes an irreplaceable and pivotal role in diverse fields including biology, medicine, chemical engineering, and environmental science. Herein, a series of cerium–tin oxide catalysts, denoted as Ce-Sn(x: y)-T, were synthesized via the co-precipitation method. The structure of the catalysts was characterized by means of X-ray diffraction, X-ray photoelectron spectroscopy, N₂ adsorption–desorption measurement, transmission electron microscopy, and so forth. The catalytic activity of Ce-Sn (x: y)-T was evaluated in the reaction of synthesizing ε-caprolactone via the oxidation of cyclohexanone with oxygen, and the optimal cerium–tin ratio and calcination temperature conditions for the preparation of the catalyst were obtained. The results indicated that there was a synergistic effect between Ce and Sn in the cerium–tin catalysts. Furthermore, a portion of Sn could incorporate into the lattice of CeO₂ to form a cerium–tin solid solution, which increased the ratio of Ce³⁺/Ce⁴⁺ and the content of oxygen vacancies in the catalyst, thus improving the oxidation performance of the catalyst. Among them, the catalyst Ce-Sn(2:1)-500 exhibited the best catalytic performance. Under the optimal reaction conditions, the conversion rate of cyclohexanone could reach 91.41%, and the selectivity of ε-caprolactone was 91.46%.