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

The amorphous SiO2-Al2O3 supported Co3O4 catalysts were prepared by impregnation method and characterized by SEM, BET, XRD, XPS, NH3-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 Co3O4/SiO2-Al2O3 catalysts possess both Lewis and Bronsted acid sites and the amount of the Bronsted acid sites increases with the increment of the loading content of cobalt. The 20% Co3O4/SiO2-Al2O3 catalyst calcinated at 500 degrees C shows relative larger surface area and pore diameter, smallest and uniform particle size, well dispersed of Co3O4. And it has the largest amount of Bronsted acid sites because it occupies the highest content of cobalt and Co2+. The relationship between the catalytic performances and the characterization results suggests that the Bronsted acid sites are the selective sites for the cyclohexane nitrosation to epsilon-caprolactam. The 20% Co3O4/SiO2-Al2O3 calcinated at 500 C gives the best result of conversion of 11.2% and epsilon-caprolactam selectivity of 83.3%, which is the best result since one step synthesis of epsilon-caprolactam from cyclohexane nitrosation was developed. (C) 2012 Elsevier B.V. All rights reserved.