Application of liquid phase deposition method for preparation of Co/ZrOx/SiO2 catalyst with enhanced Fischer–Tropsch synthesis activity: Importance of Co–Zr interaction Original Research Article

Liquid phase deposition (LPD) method using (NH4)2ZrO(CO3)2 was applied to modifying chemical nature of SiO2 surface with ZrOx species. ZrOx-modified SiO2 was then impregnated with Co nitrate solution for preparation of Co/ZrOx/SiO2 catalysts with 5 and 20 mass% Co loadings. Modification of SiO2 surface with ZrOx using the LPD method enhanced FTS activity of the Co/ZrOx/SiO2 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 SiO2 with ZrOx. H2-TPR, XRD and hydrogen chemisorption measurements revealed that modification of SiO2 surface with ZrOx using the LPD method enhanced dispersion of Co0 without loss of high reducibility of Co. However, degree of Co0 dispersion was less than that expected from enhancement of activity for the catalysts induced by ZrOx modification, indicating that turnover frequency (TOF) increased in the presence of ZrOx. 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/ZrOx/SiO2 catalysts. It was suggested that the formation of such specific interaction was responsible for not only enhancement of Co0 dispersion but also increase in TOF of the ZrOx modified catalysts.