Catalytic decomposition of N2O over Y-Co3O4 composite oxides prepared by one-step hydrothermal method

Abstract

Abstract Y-Co3O4 catalysts with Y/Co molar ratio of 0.03 were prepared by several methods, such as one-step hydrothermal, two-step hydrothermal, and impregnation methods, to catalyze the decomposition of N2O. Among these catalysts, the one prepared by one-step hydrothermal method exhibited the highest activity, and then the Y-Co3O4 catalysts with various molar ratios of Y/Co were synthesized by one-step hydrothermal method. Subsequently, the optimized 0.03Y-Co3O4 was impregnated by K2CO3 solution to prepare K-modified catalyst and named as 0.02K/0.03Y-Co3O4. These catalysts were characterized by X-ray diffraction (XRD), nitrogen physisorption, hydrogen temperature-programmed reduction (H2-TPR), oxygen temperature-programmed desorption (O2-TPD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) techniques. The results show that both Co3O4 and Y-Co3O4 exhibit spinel structure, however Y-doped Co3O4 catalysts are more active than bare Co3O4. After further modified by potassium, the 0.02K/0.03Y-Co3O4 reveals higher activity due to the more active sites (Co2+) and easier desorption of surface oxygen species than un-modified 0.03Y-Co3O4. In detail, the temperatures of N2O full conversion over 0.02K/0.03Y-Co3O4 catalyst are 325, 350, 375°C, under the reaction atmospheres of 1%N2O+Ar, 1%N2O+2%O2+Ar, 1%N2O+2%O2+8.2%H2O+Ar, respectively. In addition, over 90% conversion of N2O can be maintained at 350°C after continuous reaction for 50 h in the co-presence of oxygen and steam on K-modified Y-Co3O4 catalyst. There is a dynamic compensation effect between apparent activation energy (Ea) and pre-exponential factor (A) in N2O decomposition over Y-Co3O4 and K-modified catalysts.