Influence of Ultrasound Impregnation on the Performance of Co/Zr/SiO2 catalyst during Fischer-Tropsch Synthesis

A Co/Zr/SiO2 catalyst for Fischer-Tropsch synthesis was prepared under an ultrasound environment. The influence of different ultrasonic powers on catalyst performance was studied. The catalysts were characterized by N2 physisorption, X-ray diffraction, H2 temperature-programmed desorption, H2 temperature-programmed reduction, and transmission electron microscopy. The results show that ultrasound assisted in increasing the BET surface area of the catalysts and the even the dispersion of small cobalt crystallites on the support. When higher power ultrasound was used these characteristics of the catalyst changed remarkably. The pH of the Co(NO3)2 aqueous solution decreased with an increase in high power ultrasound treatment time, which led to a weak interaction between the smaller cobalt particles and the silica support. In addition, less cobalt silicate was formed on the catalyst. Under the same reaction conditions, the catalyst activity and stability were superior to that of the other catalysts because of higher dispersion and reduction. For example, the initial conversion of CO was 95.5% at 493 K, 2 MPa, H2/CO = 2.0, and GHSV = 1000 h−1, and it was 90.9% after 48 h.