Zeolite Catalysts for Green Production of Caprolactam

Caprolactam is an important petrochemical platform molecule that has been widely used to prepare nylon-6 and other polyamide engineering plastics. Compared with traditional routes in caprolactam synthesis with environmentally unfriendly wastes, a recent green route involves benzene semihydrogenation, cyclohexene hydration, cyclohexanol dehydrogenation, cyclohexanone ammoximation, and Beckmann rearrangement. In most of these reactions, zeolite catalysts have displayed crucial roles, for example, ZSM-5 zeolite for hydration, TS-1 zeolite for ammoximation, and S-1 zeolite for Beckmann rearrangement. In this Review, these processes and the catalytic performances of different zeolite catalysts are summarized, and the significant advantages of zeolites compared with the previous homogeneous catalysts and general supported catalysts are mentioned. In addition, the structure–performance interplay of these zeolites was particularly discussed, which is expected to guide the development of more efficient zeolite catalysts with optimized structures in the future.