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

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℃, 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℃ 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 (E_a) and pre-exponential factor (A) in N₂O decomposition over Y-Co₃O₄ and K-modified catalysts.