锡基复合氧化物功能材料研制及其低温储存NO_X性能研究

发布时间：2018-02-28 03:24

本文关键词： 稀燃尾气氮氧化物储存锡基复合氧化物抗硫　出处：《清华大学》2015年硕士论文　论文类型：学位论文

【摘要】：氮氧化物的低温去除是柴油车尾气净化的难点之一。本论文研究了锡基改性材料的低温NOX储存性能,并通过物理、化学表征手段分析了不同元素改性后材料的物理结构、氧化还原性质以及表面物种变化情况。主要结论如下:掺杂Ce元素改性后Mn-Sn复合氧化物的NOX储存性能明显升高,其中Mn/Sn/Ce比例为4/5/1的Mn0.4Sn0.5Ce0.1在100 oC时具有最高的NOX储存容量,达到435.37μmol/g。结合物理化学表征结果,发现掺杂Ce主要有三方面的作用:第一,降低晶粒尺寸,提高材料比表面积,使更多活性吸附位暴露在材料表面;第二,提高Mn-Sn-Ce材料表面活性氧物种浓度,加强材料的NO氧化能力;第三,Ce-Sn存在协同作用,可以提供大量的NOX吸附位点。采用两种制备方法对Mn0.4Sn0.5Ce0.1进行碱金属K掺杂改性,发现浸渍法制备的K/MnSnCe在100 oC的NOX储存容量降低,而共沉淀法制备的0.2K-MnSnCe在100 oC表现出较好的NOX储存容量,达到479.6μmol/g。分析表明,在共沉淀法改性材料中K可以更均匀地分布在体相MnSnCe材料中,生成新物种K2Mn4O8,不但不会覆盖MnSnCe表面的反应活性位,而且可以提供一定量的NOX储存碱性位。随后考察了实际反应气氛对低温NOX储存的影响,发现反应温度、氧气浓度、尾气中的碳氢化合物和水蒸气都会影响材料的NOX储存性能。由于含锰材料易与SO2反应生成难降解的硫酸盐,抗硫性能差,因此本研究初步探索了无锰的Sn-Co-X(X=Fe、La、Ce)复合金属氧化物的NOX储存及抗硫能力。发现新鲜的Sn-Co-Fe在100 oC具有585.35μmol/g的NOX储存容量,硫化处理后仍然表现出308.83μmol/g的NOX储存容量。四种材料的抗硫能力表现为Sn-Co-FeSn-Co-LaSn-Co-CeSn-Co。XPS表征结果显示,硫化后的Sn-Co-Fe表面具有相对较高的活性氧物种浓度,有利于NOX的储存。
[Abstract]:Low temperature removal of nitrogen oxides is one of the difficulties in diesel exhaust purification. In this paper, the storage properties of tin based modified materials at low temperature NOX were studied, and the physical structures of the modified materials were analyzed by physical and chemical characterization. Redox properties and surface species changes. The main conclusions are as follows: the NOX storage performance of Mn-Sn composite oxides modified by ce is significantly improved, and Mn0.4Sn0.5Ce0.1 with Mn/Sn/Ce ratio of 4 / 5 / 1 has the highest NOX storage capacity at 100oC. The results of physicochemical characterization show that ce doping has three main functions: first, decrease the grain size, increase the specific surface area of the material, and expose more active adsorption sites to the surface of the material. By increasing the concentration of active oxygen species on the surface of Mn-Sn-Ce, the oxidation ability of no was strengthened. Third, Ce-Sn had synergistic effect, which could provide a large number of NOX adsorption sites. Two kinds of preparation methods were used to modify Mn0.4Sn0.5Ce0.1 by alkali metal K doping. It was found that the storage capacity of K / MnSnCe at 100oC was lower than that of 0.2K-MnSnCe prepared by co-precipitation method at 100oC, and that the storage capacity of 0.2K-MnSnCe prepared by co-precipitation method was 479.6 渭 mol / g at 100oC. In the coprecipitation modified materials, K can be more evenly distributed in bulk MnSnCe materials, and a new species K _ 2mn _ 4O _ 8 is formed, which does not cover the reactive sites on the surface of MnSnCe. The effect of actual reaction atmosphere on NOX storage at low temperature was investigated, and the reaction temperature and oxygen concentration were found. Both hydrocarbons and water vapor in tail gas will affect the NOX storage performance of the materials. Because manganese containing materials react with SO2 to form sulphate which is difficult to degrade, the sulfur resistance of the materials is poor. In this study, the NOX storage and sulfur resistance of manganese free Sn-Co-XCX XFE La-Ce-based composite metal oxides were preliminarily investigated. It was found that fresh Sn-Co-Fe had a NOX storage capacity of 585.35 渭 mol/g at 100oC. After vulcanization, the storage capacity of NOX was 308.83 渭 mol/g. The sulfur resistance of the four materials was characterized by Sn-Co-FeSn-Co-LaSn-Co-CeSn-Co.XPS characterization. The results showed that the surface of cured Sn-Co-Fe had relatively high concentration of reactive oxygen species, which was favorable to the storage of NOX.
【学位授予单位】：清华大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X701

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