Catalytic decomposition of N2O over Y-Co3O4 composite oxides prepared by one-step hydrothermal method
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摘要: 用一步水热、分步水热、浸渍等方法分别制备Y-Co3O4复合氧化物,用于催化分解N2O的反应,其中,一步水热法制备的催化剂活性较高。再用一步水热法制备了不同Y/Co物质的量比的Y-Co3O4复合氧化物,在优化出的催化剂(0.03Y-Co3O4)表面浸渍K2CO3溶液,制备K改性催化剂(0.02K/0.03Y-Co3O4)。用X射线衍射(XRD)、N2物理吸附、H2程序升温还原(H2-TPR)、O2程序升温脱附(O2-TPD)、扫描电镜(SEM)、X射线光电子谱(XPS)等技术表征催化剂结构。研究发现,Co3O4和Y-Co3O4同为尖晶石结构,但Y-Co3O4的催化活性显著高于Co3O4。K改性增加了催化剂表面的活性位(Co2+),还有利于吸附氧的脱除,从而提高了催化剂活性。在无氧无水、有氧无水、有氧有水气氛中,K改性催化剂上的N2O全分解温度分别为325、350、375 ℃,催化剂活性较高。有氧有水气氛350 ℃连续反应50 h,K改性催化剂上N2O分解率保持90%以上,稳定性较高。研究发现,Y-Co3O4及K改性催化剂上N2O分解反应的Ea和lnA之间存在动力学补偿效应。
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关键词:
- N2O催化分解 /
- Y-Co3O4复合氧化物催化剂 /
- K改性催化剂 /
- 一步水热合成 /
- 催化活性
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℃, 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 (Ea) and pre-exponential factor (A) in N2O decomposition over Y-Co3O4 and K-modified catalysts.-
Key words:
- catalytic decomposition of N2O /
- Y-Co3O4 composite oxides /
- K-modified catalyst /
- one-step hydrothermal method /
- catalytic activity
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Table 1 Specific surface area of Y-Co3O4 catalysts with various Y/Co molar ratios
Y-Co3O4 catalyst Specific surface area A/(m2·g-1) Co3O4 28.5 Y/Co=0.01 47.7 Y/Co=0.02 61.2 Y/Co=0.03 72.7 Y/Co=0.04 70.8 Y/Co=0.05 80.3 Table 2 Kinetic data of N2O decomposition on Y-Co3O4 catalysts with various Y/Co molar ratios
Catalyst k/s-1 Ea/(kJ·mol-1) lnA 275 ℃ 300 ℃ 325 ℃ 350 ℃ 375 ℃ Co3O4 0.26 0.67 1.37 3.02 4.73 86.7 17.7 Y/Co=0.01 0.41 1.18 2.49 4.58 7.29 79.9 16.9 Y/Co=0.02 0.51 1.17 2.50 4.47 7.15 78.5 16.6 Y/Co=0.03 0.50 1.25 2.58 4.57 6.77 77.6 16.4 Y/Co=0.04 0.29 0.90 2.02 3.80 6.28 90.2 18.7 Y/Co=0.05 0.26 0.87 1.82 3.49 5.81 90.7 18.7 Table 3 Kinetic data of N2O decomposition over 0.03Y-Co3O4 and K-modified catalysts under various reaction atmospheres
Reaction atmospheres 0.03Y-Co3O4 catalyst 0.02K/0.03Y-Co3O4 catalyst Ea /(kJ·mol-1) lnA Ea /(kJ·mol-1) lnA 1%N2O+Ar 77.6 16.4 63.9 15.5 1%N2O+2%O2+Ar 91.6 18.7 76.6 18.0 1%N2O+2%O2+8.2%H2O+Ar 110.0 20.6 86.8 19.2 -
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