xK/MgAlO型催化剂催化碳烟燃烧的机理研究

Research on the mechanism of xK/MgAlO hydrotalcite for the catalytic combustion of soot

通过等体积浸渍法制备了不同K掺杂量的镁铝水滑石复合氧化物(xK/MgAlO),利用X射线衍射光谱及暂态响应、扫描电子显微镜、傅里叶变换红外光谱、X射线光电子能谱及程序升温等技术比较了焙烧和未焙烧的MgAlO形貌结构和晶型的异同,在含硫气氛中研究了K对镁铝水滑石复合氧化物形貌结构和催化碳烟燃烧性能的影响,阐明了反应过程中K掺杂的xK/MgAlO型催化剂降低碳烟起燃温度的关键机制。结果表明,焙烧后的镁铝水滑石3R层状结构消失,出现了尖晶石相,层状结构坍塌变为球形颗粒状;掺杂钾后的催化剂(K/MgAlO)表面活性氧与晶格氧的比例增大,使得氧空位的数量增多,有效提高了催化剂的催化反应活性。在模拟烟气实验中发现掺杂量x=7的(7K/MgAlO)催化剂在含SO_2的混合气中使碳烟的起燃温度降低了127℃,且对NO_x的转化率显著增强。

The Mg-Al hydrotalcites used as the support were prepared by precipitation method,and then the catalysts with different amount of doped potassium,(x K/MgAlO)were prepared by impregnation method.The effects of K on the structure and catalytic activity of the x K/MgAlO catalyst were investigated in SO 2 containing gases.The key mechanism of K-doped(x K/MgAlO)catalysts to reduce the soot ignition temperature during the reaction was illustrated.The differences of the crystal structure between calcined and uncalcined Mg-Al hydrotalcite were studied by X-ray diffraction,scanning electron microscopy,Fourier transform infrared spectroscopy,and the transient response method.The experimental results showed that the 3R layered structure of Mg-Al hydrotalcite disappeared while the spinel phase appeared,and the layered structure collapsed into spherical particles after calcination.Potassium doping formed more oxygen vacancies that are conducive to the combustion of diesel soot,decreased the temperature of soot combustion from 380 to 253℃though in SO 2 atmosphere and significantly enhanced the conversion efficiency of NO x.