【作者】 魏丽斯；

【导师】 李俊华；

【作者基本信息】 清华大学 ， 环境科学与工程， 2009， 硕士

【摘要】 氮氧化物储存还原技术（NO_X Storage-Reduction,NSR）可以有效去除稀燃机动车尾气中NO_X,但是如何在较低温度条件下提高催化剂的NO_X储存性能是国内外学术界的研究热点。本研究采用水热合成方法制备了不同前驱体的三种MnO_X-SnO₂催化剂（HH、MH和CH）,考察了其在100℃时的NO_X吸附性能,并系统地研究了MH方法制备的不同Mn/Sn比例的催化剂的吸附性能,利用比表面积测试（BET）、X射线衍射（XRD）、程序升温还原（TPR）、X射线光电子能谱（XPS）以及原位漫反射红外光谱（DRIFTS）等手段对催化剂进行了表征。主要研究结果如下:不同前驱体制备的三种MnO_X-SnO₂催化剂在100℃都具有良好的NO氧化能力和NO_X储存能力,其中以MH催化剂效果最好。在MH和HH催化剂中Mn物种主要是Mn4+,CH催化剂中Mn物种主要为Mn³⁺,Mn的高氧化态更有利于NO_X的储存。XPS的结果显示,缺陷氧物种或表面处于低配位的氧物种在MnO_X-SnO₂催化剂低温储存NO_X的过程中也起到重要的作用。不同Mn/Sn比例的MnO_X-SnO₂（MH）催化剂在100℃下都具有一定的NO_X储存能力,其中Mn₅Sn0和Mn0Sn₅效果较差,Mn2Sn3催化剂效果最好。表征结果表明,在MnO_X-SnO₂（MH）系列催化剂制备过程中,MnO_X和SnO₂在制备的过程中部分形成了固溶体,比表面积增大,氧化性增强,吸附活性位增加,从而使得催化剂的低温储存NO_X量得到大大提高。原位漫反射红外光谱研究表明:MnO_X的催化氧化性很强,但NO吸附活性位较少,主要以吸附NO₂转化成硝酸盐的方式储存NO_X,SnO₂的氧化性很弱,但NO吸附位点较多,可以主要以吸附NO转化成亚硝酸盐的方式储存NO_X,而部分亚硝酸盐也可以被氧化成硝酸盐。MnO_X-SnO₂催化剂上Mn和Sn在储存NO_X时形成了明显的协同作用,从而提高了催化剂低温NO_X储存性能。更多还原

【Abstract】 The NO_X storage reduction （NSR） technology can effectively remove the NO_X in the presence of excess oxygen from lean burn engine exhaust. However, the low-temperature NO_X storage capacity （NSC） of NSR catalyst is still unsatisfactory due to the the low NO oxidation rate at relatively low temperature region. In this work, MnO_X-SnO₂ binary metal oxides were prepared by three hydrothermal methods with different precursors and were donated as HH, MH and CH respectively. A series of catalysts perpared with different ratio of Mn/Sn have been studied. These catalysts have been investigated on their performance on NO_X storage capability at 100℃. They have been characterized by BET, X-ray Diffraction, Temperature Programmed Reduction, X-ray Photoelectron Spectroscopy, and in-situ Diffuse- Reflectance Infrared Fourier Transform Spectroscopy. The main results were summarized as follows:The HH, MH and CH catalysts all showed good performance on NO oxidation capacity and NO_X storage capability, especially for the MH catalyst. In the HH and MH catalysts, manganese species were dominantly presented as Mn4+, whereas Mn³⁺ was the dominant species in the CH catalyst. The high oxidation state of Mn was beneficial to NO storage. XPS results revealed that the defect oxide or the surface oxygen ions with low coordination might play an important role in the NO_X adsorption.The catalysts perpared with various ratio of Mn/Sn showed different NSC at 100℃. The Mn2Sn3 catalyst showed the longest breakthough time and the highest NO_X storage capacity; whereas Mn5Sn0 and Mn0Sn5 showed lower NSC. According to characterization results, it can be concluded that MnO_X and SnO₂ partialy formed solid solution in the preparation process. As a result, The BET surface areas of the samples became larger, NO oxidation was enhanced and due to the increase of NO adsorption sites, and then the NO_X storage capacity were improved at the low temperature.DRIFTS results revealed that MnO_X showed high NO oxidation capacity and poor NO adsorption sites. NO₃^- formed by NO₂ adsorption was the main species on the surface of the MnO_X catalyst. SnO₂ with low NO oxidation capacity and rich NO adsorption sites could direct adsorb NO and form NO₂-. And then NO₂^- partialy changed to NO₃^-. Therefore, on the surface of the MnO_X-SnO₂ catalyst, Mn and Sn showed an obvious co-operative effect in the process of NO_X adsorption/desorption, which resulted in the improvement of the NO_X storage capacity at low temperature.更多还原