分别采用甘氨酸硝酸盐法、溶胶凝胶法、共沉淀法、燃烧法以及水热法制备了钙钛矿型LaMn0.8Mg0.2O3复合氧化物,用X射线衍射、红外光谱、H2程序升温还原和低温N2吸附对其进行了表征,并考察了其对甲烷燃烧的催化活性.结果表明,制备方法和焙烧温度对LaMn0.8Mg0.2O3钙钛矿型催化剂的结构、晶粒大小和不同类型的氧物种影响很大.以甘氨酸硝酸盐法制备的钙钛矿型催化剂经700℃焙烧后表现出最高的催化活性,T50烷转化率达到50%时的温度)仅为440℃.这归结于它较小的晶粒尺寸(12.4nm)和较大的比表面积(18.6m2/g),以及催化剂表面富集的Mn4+,从而使表面氧物种更容易移动和/或更具有反应活性.
A perovskite-type composite oxide, LaMn0.8Mg0.2O3, was prepared by five methods, i.e., glycine-nitrate, sol-gel, co-precipitation,combustion synthesis, and hydrothermal treatment. The composites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, H2-temperature-programmed reduction, and N2 adsorption-desorption isotherms. The catalytic activity of LaMn0.8Mg0.2O3 toward methane combustion was evaluated. The results show that the different preparation methods and calcination temperatures greatly influence the textural structure, crystallite size, and different oxygen species within the LaMn0.8Mg0.2O3 perovskite material. The perovskite catalyst synthesized by the glycine-nitrate method and calcined at 700 ℃ shows the best activity for methane combustion among the tested materials.Its T50 (the reaction temperature at which 50% CH4 is converted) is only ～440 ℃. This good catalyst performance can be attributed to the small crystallite size (12.4 nm), larger surface area (18.6 m2/g), and high concentration of surface Mn4+ cations, which creates more flexible and reactive surface oxygen species.
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