Preparation of mesoporous SiO 2–Al 2O 3 supported Co or Mn catalysts and their catalytic properties in cyclohexane nitrosation to ɛ-caprolactam

Abstract

Mesoporous crystalline SiO 2–Al 2O 3 was prepared by hydrothermal synthesis method and its supported Co or Mn catalysts were prepared by impregnation method. These prepared materials were characterized by XRD, XPS, NH 3–TPD, BET, FT-IR and TG–DSC. It reveals that the metals are substituted into the framework as the form of MnCo 2O 4, Mn 3O 4, MnO, Co 3O 4 and stronger acid sites appear. Furthermore, Pyridine FT-IR spectra and NH 3–TPD results indicate that both Brønsted and Lewis acid sites exist on these SiO 2–Al 2O 3 supported transition metal catalysts and Mn/SiO 2–Al 2O 3 exhibits higher Brønsted acid content. BET results show that SiO 2–Al 2O 3 with middle Si/Al molar ratio has larger surface area and pore volume. The surface area and pore volume of SiO 2–Al 2O 3 decrease after the introduction of the transition metals. The catalytic properties in the cyclohexane nitrosation to ɛ-caprolactam were performed and Mn/SiO 2–Al 2O 3 exhibits better activity and selectivity to the ɛ-caprolactam.