Preparation of mesoporous SiO2–Al2O3 supported Co or Mn catalysts and their catalytic properties in cyclohexane nitrosation to ɛ-caprolactam

Mesoporous crystalline SiO2–Al2O3 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, NH3–TPD, BET, FT-IR and TG–DSC. It reveals that the metals are substituted into the framework as the form of MnCo2O4, Mn3O4, MnO, Co3O4 and stronger acid sites appear. Furthermore, Pyridine FT-IR spectra and NH3–TPD results indicate that both Brønsted and Lewis acid sites exist on these SiO2–Al2O3 supported transition metal catalysts and Mn/SiO2–Al2O3 exhibits higher Brønsted acid content. BET results show that SiO2–Al2O3 with middle Si/Al molar ratio has larger surface area and pore volume. The surface area and pore volume of SiO2–Al2O3 decrease after the introduction of the transition metals. The catalytic properties in the cyclohexane nitrosation to ɛ-caprolactam were performed and Mn/SiO2–Al2O3 exhibits better activity and selectivity to the ɛ-caprolactam.

Mesoporous crystalline SiO2–Al2O3 and its supported Co or Mn catalysts were prepared and characterized. The catalytic properties of these catalysts in cyclohexane nitrosation to ɛ-caprolactam were investigated and a possible mechanism for liquid phase nitrosation of cyclohexane was proposed.Figure optionsDownload high-quality image (98 K)Download as PowerPoint slideHighlights
► One-pot synthesis of ɛ-caprolactam catalyzed by mesoporous crystalline Mn/SiO2–Al2O3.
► Brønsted acid caused by metal oxide species is helpful to cyclohexane nitrosation.
► Metals’ load decreases the activity while increases the selectivity to ɛ-caprolactam.
► A possible mechanism for liquid phase nitrosation of cyclohexane is proposed.