锰基氧化物制备及其选择催化氧化氨性能研究

发布时间：2018-01-13 20:05

  本文关键词：锰基氧化物制备及其选择催化氧化氨性能研究　出处：《大连理工大学》2015年硕士论文　论文类型：学位论文

  更多相关文章： 锰基催化剂 NH_3-SCO 尿素 沉淀法

【摘要】：氨气(ammonia, NH3)是一种典型的有毒工业废气,会对人体健康和生态环境产生严重的危害。因此,近年来对氨的控制和治理引起了人们的广泛关注。目前存在的氨处理技术有很多,选择性催化氧化法因其高效、快捷、无二次污染等特点,成为了消除含氨废气的首选。贵金属催化剂虽表现出良好的低温活性,但价格昂贵、N2选择性低；过渡金属催化剂虽价格低廉,有很好的N2选择性,但完全转化温度高,耗能大,不利于工业应用。本论文通过采用不同合成方法制备锰基氧化物催化剂并测试其氨氧化活性,并通过考察催化剂结构性质,研究结构与活性间的关系。主要研究如下：1.采用沉淀法合成Mn-Ce复合氧化物催化剂并对其进行氨选择性催化氧化性能研究。实验发现：以n(urea)/n(Mn+Ce)=10:1的尿素作为沉淀剂,经400℃焙烧得到的n(Mn):n(Ce)为4:1的Mn-Ce复合氧化物表现出较优的氨氧化活性,在200℃即实现了氨的完全转化。2.采用水热沉淀法合成Mn-Ce复合氧化物催化剂并对其进行氨选择性催化氧化性能研究。实验发现：对沉淀过程中的锰源以及反应温度、压力进行调节,可明显影响催化剂的氨氧化性能。以Mn2+和MnO4-同时为锰源,在1408水热条件下合成的Mn-Ce复合氧化物表现出更好的氨氧化活性,在180℃即能实现氨的完全转化。结合表征结果发现：水热沉淀法中引入KMnO4,可提高Mn-Ce复合氧化物的比表面积,促使Mn4+进入Ce02立方萤石结构中形成Mn-Ce-O固溶体,促进氧的流动,从而提高催化剂的氧化还原能力,提高其氨氧化性能。3.采用水热沉淀法合成纯锰氧化物催化剂并对其进行氨选择性催化氧化性能研究。实验发现：水热沉淀法合成的MnO2(UH)催化剂在170℃即可实现氨的完全转化,N2选择性为49%。并通过与水热法合成的MnO2(H)催化剂以及商业Mn02进行对比研究,结合XRD、BET、H2-TPR、SEM、XPS、NH3-TPD结果可知,合成过程中加入一定量的尿素可以对催化剂结构进行调变,使催化剂颗粒均匀分散且尺寸减小,并在保持α-MnO2晶相不变的情况下实现了催化剂形貌从纳米棒到纳米片的转变,大量纳米片又进一步交叉聚集形成花状的微粒小球,显著提高了催化剂的比表面积,在其表面形成大量的吸附位点和氧空穴,促进了污染物和分子态氧的吸附和活化,从而提高了催化剂的氨氧化活性。
[Abstract]:Ammonia ammonia (NH3) is a typical toxic industrial waste gas, which will cause serious harm to human health and ecological environment. In recent years, the control and treatment of ammonia has attracted wide attention. There are many ammonia treatment technologies, and selective catalytic oxidation process is characterized by its high efficiency, rapidity, no secondary pollution and so on. Noble metal catalysts showed good low temperature activity, but the selectivity of N2 was low. Although the transition metal catalyst has the advantages of low price and good N2 selectivity, the complete conversion temperature is high and the energy consumption is high. In this thesis, manganese based oxide catalysts were prepared by different synthesis methods and their ammonia oxidation activities were tested, and the structure and properties of the catalysts were investigated. The relationship between structure and activity was studied. The main results were as follows: 1. The Mn-Ce composite oxide catalyst was synthesized by precipitation method and its ammonia selective catalytic oxidation performance was studied. Urea of urea)/n(Mn Ce)=10:1 is used as precipitant. The Mn-Ce composite oxides calcined at 400 鈩，

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