Application of liquid phase deposition method for preparation of Co/ZrO x/SiO 2 catalyst with enhanced Fischer–Tropsch synthesis activity: Importance of Co–Zr interaction

Abstract

Liquid phase deposition (LPD) method using (NH 4) 2ZrO(CO 3) 2 was applied to modifying chemical nature of SiO 2 surface with ZrO x species. ZrO x -modified SiO 2 was then impregnated with Co nitrate solution for preparation of Co/ZrO x /SiO 2 catalysts with 5 and 20 mass% Co loadings. Modification of SiO 2 surface with ZrO x using the LPD method enhanced FTS activity of the Co/ZrO x /SiO 2 catalysts under the reaction conditions of 503 K and 1.1 MPa. The LPD method was superior to other method reported previously such as impregnation and sol–gel methods in terms of surface modification of SiO 2 with ZrO x . H 2-TPR, XRD and hydrogen chemisorption measurements revealed that modification of SiO 2 surface with ZrO x using the LPD method enhanced dispersion of Co 0 without loss of high reducibility of Co. However, degree of Co 0 dispersion was less than that expected from enhancement of activity for the catalysts induced by ZrO x modification, indicating that turnover frequency (TOF) increased in the presence of ZrO x . This effect was particularly important for the catalyst with the low Co loading. Furthermore, in situ DRIFT measurement provided evidence for the formation of specific interaction of Co species with Si–OH and Zr–OH species in the Co/ZrO x /SiO 2 catalysts. It was suggested that the formation of such specific interaction was responsible for not only enhancement of Co 0 dispersion but also increase in TOF of the ZrO x modified catalysts.