N_2O分解催化剂Co-Al尖晶石型复合氧化物制备参数的优化

以柠檬酸为配合剂,用溶胶-凝胶法制备了一组不同组成的Co-Al复合氧化物(CoAl_2O_4、CoCo0.5Al1.5O4、CoCoAlO_4、CoCo_(1.5)Al_(0.5)O_4、Co_3O_4),用于催化分解N_2O.用N_2物理吸附、X射线衍射(XRD)、扫描电镜(SEM)、H2程序升温还原(H2-TPR)、X射线光电子能谱(XPS)等技术对催化剂进行了结构表征,考察了复合氧化物组成、母液pH值、配合剂用量等制备参数对催化剂活性的影响.结果表明:用Al取代Co_3O_4中部分Co制备Co-Al复合氧化物,提高了催化剂的比表面积和催化活性,其中组成为CoCo_(1.5)Al_(0.5)O_4、母液pH=2、柠檬酸/金属离子(摩尔比)为1的催化剂活性较高.在CoCo_(1.5)Al_(0.5)O_4表面浸渍K2CO3溶液制得K改性催化剂,弱化了钴-氧化学键,提高了催化活性.其中0.02K/CoCo1.5Al0.5O4催化剂在有氧有水气氛400℃连续反应50h,N_2O转化率达97.1%.

The Preparation Parameters Screening of Co-Al Spinel Oxides for N2O Catalytic Decomposition

A series of Co-Al mixed oxides, such as CoAl2O4, CoCo0.5Al1.5O4, CoCoAlO4, CoCo1.5Al0.5O4, Co3O4, were prepared by sol-gel method using citric acid as chelating agent and applied in N2O decomposition reaction. These catalysts were characterized by means of techniques such as N2 physisorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature-programmed reduction of hydrogen (H2-TPR), and X-ray photoelectron spectroscopy (XPS). The effect of mixed oxides compositions, pH values of mother liquid, and chelating agent contents on catalysts activity was investigated. The results show that that the replacement of Co in Co3O4 by Al increased the specific surface area and enhanced the catalytic activity. Of these Co-Al mixed oxides, the optimal one was CoCo1.5Al0.5O4 with mother liquid pH value of 2 and the molar ratio of nitric acid to total metallic ions of 1. In the case of K2CO3-modified CoCo1.5Al0.5O4 catalyst, we found that the electron density of cobalt species was increased and oxygen species removal was promoted, thus Co-O bond was weakened and N2O decomposition was enhanced. Of these K-modified catalysts, 0.02K/CoCo1.5Al0.5O4 exhibited good catalytic activity and stability, e.g. N2O conversion kept 97.1% at 400C after continuous reaction for 50h even in the co-presence of oxygen and steam.