题名高活性CuO-CeO2催化剂的制备及其催化氧化苯的性能研究
作者胡超权
学位类别博士
答辩日期2009-05-27
授予单位中国科学院过程工程研究所
授予地点过程工程研究所
导师朱庆山
关键词挥发性有机物 催化氧化 多相催化 CuO-CeO2 苯氧化
其他题名Preparation of Highly Active CuO-CeO2 Catalysts and Their Catalytic Performance for Benzene Oxidation
学位专业化学工程
中文摘要挥发性有机物是环境污染源中一类重要的污染源,它不仅会造成环境污染,而且对人类健康危害也很大,因此消除挥发性有机物引起了人们的重视。在所有挥发性有机物中,苯是一种工业生产中非常常见的污染物,由于其毒性大,因此相关法律法规对其排放标准非常严格。如何消除空气中低浓度的苯是目前的研究热点之一。 催化氧化技术是消除工业源排放挥发性有机物的主要技术之一,催化剂的性能是决定这一技术效能的重要因素。在众多催化剂中,CuO-CeO2混合氧化物被认为是一类非常具有应用前景的催化剂。但CuO与CeO2形成固溶体的范围非常小,且CuO耐热性差、易迁移、高温失活严重,因此CuO-CeO2催化剂中CuO的含量通常都较低,导致CuO-CeO2混合氧化物催化剂对挥发性有机物的催化氧化活性难提高。另外,CuO-CeO2热稳定性差,催化剂在高温连续反应下失活非常严重,因此提高CuO-CeO2催化剂的热稳定性也是一个非常重要的方面。 为了解决上述问题,本论文开展了以下几个方面的工作: (1)通过合成具有高比表面积的介孔CuO-CeO2催化剂来提高其对苯的催化氧化活性。这是因为高的比表面积能提供更多的活性中心,而介孔有利于消除催化反应过程中大分子有机物造成的扩散控制效应的影响。与传统模板法不同,本研究中开发的合成介孔的方法主要基于硝酸铵的分解,该方法不仅具有廉价、快速等特点,而且具有一定的通用性,也适用于制备其它介孔二元氧化物体系,如CeO2-ZrO2和Y2O3-ZrO2体系。实验结果表明,本研究中合成的介孔CuO-CeO2催化剂对苯的催化完全氧化反应中表现出较高的活性,脉冲实验表明苯在CuO-CeO2催化剂上的反应行为符合氧化-还原机制。但该介孔CuO-CeO2催化剂在260oC下连续反应10h后,比表面积严重下降,对苯的氧化性能也随之降低。 (2)为了降低比表面积的影响,通过探索合成了CuO-CeO2催化剂新的纳米结构来提高其对苯的催化氧化活性。对这种片状纳米结构的形成机理研究表明,纳米片的形成主要是由纳米颗粒之间的团聚造成的,并且这种方法同样也适用于合成MnO-CeO2二元体系纳米片状结构。虽然CuO-CeO2纳米片催化剂比表面积较小,但由于在这种结构中CuO能充分暴露在催化剂的表面,因此其对苯表现出良好的催化性能。但CuO-CeO2片状催化剂的热稳定性也较差,在240oC连续反应30h后即出现明显失活现象。高度分散的CuO形成块状晶相CuO可能是其催化性能降低的重要原因。 (3)为了提高CuO-CeO2催化剂的热稳定性,主要通过掺杂ZrO2对CeO2进行改性来提高催化剂的稳定性。采用超临界干燥制备的CuO-ZrxCe1-xOy(0
英文摘要Volatile organic compounds (VOCs), emitted from many industrial processes and transportation activities, are an important class of air pollutants. They are considered as great contributors to the atmospheric pollution and to be dangerous to human health. Thus, reduction of VOCs emissions has attracted significant attention in the environment field. Among all the VOCs, benzene is widely used in modern chemical industry and causes serious pollution. Its emission standard is becoming stringent due to its serious toxicity. The reduction of the low concentration of benzene in air is an important issue in the environment field. Catalytic oxidation is one of the most important technologies for the abatement of VOCs at low concentration in effluent streams, and the activity of the catalysts employed is one of the ruling factors deciding the efficiency of this technique. Among all the catalysts, CuO-CeO2 mixed oxides has received much attention as a catalyst for oxidation reactions due to its low cost and high catalytic activity that can be comparable to noble metal catalysts. However, the range for the formation of solid solution between CuO and CeO2 is very narrow, which makes it difficult improve the catalytic activity of CuO-CeO2 catalyst. In addition, the thermal stability of the CuO-CeO2 mixed oxides catalyst is poor. Thus, the increase of the catalytic activity and the improvement of the thermal stability of the CuO-CeO2 mixed oxides catalyst are two important issues before it is widely used as a catalyst for VOCs oxidation. In order to solve the above problems, the main points in the present study are as follows: (1) Mesoporous CuO-CeO2 mixed oxides with a high BET surface area has been successfully synthesized by a simple and quick route and used as the catalyst for the benzene oxidation. Here, we chose the mesoporous structure due to its easy accessibility of the guest molecules to active sites in the multidimensional framework. The synthesis route for the mesoporous route in the present study is distinctly different from the conventional method using the supramolecular assembly of surfactant molecules as a template. The evident advantage of this method presented in this study is the simplicity of the synthesis process and the abundance, inexpensive of raw materials. Furthermore, the synthesis mechanism could be applied to synthesize CeO2-ZrO2 and Y2O3-ZrO2 with mesoporous structures, indicating the method presented here may generally be applied to the synthesis of other inorganic binary oxides with mesoporous structures. The related results showed that the as-prepared mesoporous CuO-CeO2 mixed oxides was highly active for the benzene oxidation compared to the reported catalysts. In addition, the pulse experiments have shown that the benzene oxidation over the CuO-CeO2 catalyst proceeds according to the Mars-van Krevelen mechanism. However, the surface area of the mesoporous CuO-CeO2 catalyst decreased after test for 10 h and an obvious deactivation of the catalyst was observed. (2) In order to alleviate the effect of the surface area on the catalytic performance, CuO-CeO2 mixed oxides with a sheet-like nanostructure was synthesized for the further enhancement of its catalytic activity for the benzene oxidation. The evolution of the nanosheets was examined by FESEM and the mechanism was briefly discussed. The results showed that the nanosheets were mainly formed by the aggregation of the nanoparticles. This method can also be applied to synthesize MnO-CeO2 binary oxides with sheet-like nanostructures. Though the CuO-CeO2 nanosheet catalyst had a relatively low surface area, it exhibited highly catalytic activity for the benzene oxidation due to the large amounts of CuO exposed on the surface in the catalyst. However, the thermal stability of the CuO-CeO2 nanosheet catalyst was poor and the benzene conversion decreased about 13% after test for 30 h. The formation of bulk CuO may be responsible for the deactivation of the catalyst. (3) In order to improve the thermal stability of the CuO-CeO2 catalyst, ZrO2 was incorporated into the CeO2 lattice to modify the CuO-CeO2 system. After calcined at 800oC, the CuO-ZrxCe1-xOy (0
语种中文
公开日期2013-09-13
页码139
内容类型学位论文
源URL[http://ir.ipe.ac.cn/handle/122111/1186]  
专题过程工程研究所_研究所(批量导入)
推荐引用方式
GB/T 7714
胡超权. 高活性CuO-CeO2催化剂的制备及其催化氧化苯的性能研究[D]. 过程工程研究所. 中国科学院过程工程研究所. 2009.
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