我国煤矿开采乏风瓦斯排量大.其温室效应是CO2的21倍.会引起严重的环境问题.催化燃烧作为一种高效.绿色的净化技术.在较低温度下可将低浓度甲烷完全转化.目前.甲烷催化燃烧反应的关键科学问题是氧活性位的确认及其催化机制.采用溶胶-凝胶法制备一系列不同物质的量比La/Mn的菱形钙钛矿LaMnO3-x催化剂.并考察其在甲烷催化燃烧的反应性能.通过X射线衍射.N2物理吸附.透射电子显微镜和H2-程序升温还原技术对催化剂的物化性能进行表征.此外.采用X射线光电子能谱.O2-程序升温脱附和拉曼光谱技术研究了钙钛矿LaMnO3-x中氧物种的种类和相对含量.X射线衍射结果表明.所有催化剂均为菱形钙钛矿LaMnO3结构.未观察到其他La和Mn物种的衍射峰.固定床评价结果表明.钙钛矿LaMnO3-90具有介孔孔道.比表面积较大.且具有最多的体相和表面晶格氧物种.使其催化活性最高.此外.缺陷钙钛矿LaMnO3-90具有良好的催化寿命和结构稳定性.钙钛矿LaMnO3-x催化剂的甲烷催化活性与表面晶格氧体积分数呈正相关.因此.推测表面晶格氧物种是钙钛矿LaMnO3-x催化甲烷燃烧反应的活性中心.

The emission of ventilation air methane causes serious air pollution.owing to 21 times higher greenhouse potential in comparison to CO2. Catalytic combustion of methane has received considerable attention due to its effectiveness in eliminating the trace amount of methane in the ventilation air. The key scientific problems and difficulties of the methane combustion reaction are the determination of active sites and elucidation of reaction mechanism. A series of defective rhombohedral perovskite LaMnO3 materials with different La/Mn molar ratios were prepared using the modified Pechini method.and tested in methane combustion. The as-synthesized perovskite samples were characterized by means of X-ray diffraction.N2 physisorption.transmission electron microscopy.and H2-temperature programmed reduction. In addition.the kind and relative content of oxygen species in the samples were measured by X-ray photoelectron spectroscopy.O2-temperature programmed desorption.and Raman spectroscopy techniques. The XRD results evidenced that the pure perovskite phase was simply synthesized for all the samples. The results showed that the perovskite LaMnO3-90 possessed a mesoporous structure with larger specific surface area. Moreover.the Raman.XPS.and O2-TPD results exhibited that the perovskite LaMnO3-90 had more surface lattice oxygen sites.endowing the highest methane combustion activity. The perovskite LaMnO3-90 delivered stable run without obvious deactivation owing to its structural stability. It is found that the methane conversion had a positive correlation with the concentration of surface lattice oxygen among the series LaMnO3-x catalysts. Hence.the authors speculate that the lattice oxygen in the perovskite surface may be responsible for the methane activation during the methane combustion.

1 试验

   1.1 钙钛矿催化剂制备

   1.2 催化剂表征

   1.3 催化剂评价

2 试验结果与讨论

   2.1 钙钛矿LaMnO3-x结构与可还原性

   2.2 钙钛矿LaMnO3-x催化性能

   2.3 钙钛矿LaMnO3-x催化燃烧机理

3 结论