Effect of drying method and precipitation pH in ZrO2 preparation on its structural and textural properties
Publication Date: 2004-Oct-11
The IP.com Prior Art Database
Zirconium oxide (ZrO2) has attracted considerable attention recently as both a catalyst and a catalyst support because of its high thermal stability and the amphoteric character of its surface hydroxyl groups. In this study, ZrO2 was synthesized through the precipitation of an aqueous ZrOCl2 solution at a constant pH followed by drying and then calcination at different high temperatures. We investigated the effect of drying method and precipitation pH on the structural and textural properties of ZrO2. It has been found that the method of freeze drying offers advantages over conventional evaporative drying in preparing ZrO2 support with high surface area, large pore volume and large size pores. After calcination at 1000 °C for 3 hr, a ZrO2 sample that precipitated at pH = 11 and was subsequently freeze-dried has a surface area of 4.1 m2/g, which is almost three times of the 1.5 m2/g surface area of an evaporative dried sample (Figure 1). Compared with conventional evaporative drying, freeze drying is beneficial to not only retaining higher surface area after high temperature calcination but also obtaining a ZrO2 sample with larger pore volume and larger pores as well. Freeze dried ZrO2 can possess a total pore volume up to twice that of evaporative dried samples (Figure 2). Pore distribution analysis via N2 physical adsorption reveals that the average pore diameter of freeze-dried ZrO2 is significantly larger than that of evaporative dried ZrO2 after both samples are calcined at the same temperature. Consequently, ZrO2 prepared by freeze-drying could offer advantages over evaporative dried ZrO2 when used to catalyze reactions involving large molecules.