Amorphous SiO2–Al2O3 supported Co3O4 and its catalytic properties in cyclohexane nitrosation to ɛ-caprolactam: Influences of preparation conditions

The amorphous SiO 2 –Al 2 O 3 supported Co 3 O 4 catalysts were prepared by impregnation method and characterized by SEM, BET, XRD, XPS, NH 3 -TPD and FT-IR. The influences of the preparation conditions including the loading content of cobalt and the calcination temperature were studied in detail. The results show that the supported Co 3 O 4 /SiO 2 –Al 2 O 3 catalysts possess both Lewis and Brønsted acid sites and the amount of the Brønsted acid sites increases with the increment of the loading content of cobalt. The 20% Co 3 O 4 /SiO 2 –Al 2 O 3 catalyst calcinated at 500   °C shows relative larger surface area and pore diameter, smallest and uniform particle size, well dispersed of Co 3 O 4 . And it has the largest amount of Brønsted acid sites because it occupies the highest content of cobalt and Co 2+ . The relationship between the catalytic performances and the characterization results suggests that the Brønsted acid sites are the selective sites for the cyclohexane nitrosation to ɛ-caprolactam. The 20% Co 3 O 4 /SiO 2 –Al 2 O 3 calcinated at 500   °C gives the best result of conversion of 11.2% and ɛ-caprolactam selectivity of 83.3%, which is the best result since one step synthesis of ɛ-caprolactam from cyclohexane nitrosation was developed.