Improvement of Cobalt Dispersion on Co/SBA-15 and Co/SBA-16 Catalysts by Ultrasound and Vacuum Treatments during Post-Impregnation Step
The Co/SBA-15 and the Co/SBA-16 catalysts having 20 wt% of cobalt were prepared by the conventional impregnation method. Then, the post-impregnation treatments including vacuum and ultrasound treatments were applied. The synthesized catalysts were characterized by means of N2 physisorption, small angle X-ray diffraction (SAXRD), wide angle X-ray diffraction (XRD), scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDX), transmission electron microscopy (TEM), and temperature-programmed reduction (TPR). The results show that the synthesized SBA-15 had hexagonal structure and the synthesized SBA-16 had the cubic structure. The vacuum and the ultrasound treatments after incipient wetness impregnation can apparently enhance the dispersion of cobalt on the SBA-15 catalysts due to the decrease of the metal crystallite size. However, only the vacuum treatment was suitable for the Co/SBA-16. After reduction, no cobalt-silicate compound was detected based on XRD measurement. Both post-impregnation treatments can also decrease the metal-support interaction resulting in increased activity for CO2 hydrogenation under methanation.