堇青石整体式催化剂用于柴油机尾气净化的研究

太原理工大学

硕士学位论文

Cu-ZSM-5/堇青石整体式催化剂用于柴油机尾气净化的研究

姓名：田东

申请学位级别：硕士

专业：@

指导教师：鲍卫仁;常丽萍

20100601

Cu-ZSM-5/堇青石整体式催化剂用于柴油机

尾气净化的研究

摘 要

三效催化剂(TWC)应用于汽车尾气净化时能同时去除尾气中的CO，HC和NOx，但此技术只能应用于空燃比（A/F）为14.7附近狭窄的范围内。富氧燃烧是当前提倡节约能源和减少废气排放的发展趋势。但TWC催化剂在这种燃烧条件下对NOx脱除基本没有活性。以分子筛为载体的金属/分子筛催化剂体系在该领域体现出了较好的应用前景。分子筛催化剂负载在成型的载体上，可以降低汽车尾气的阻力。堇青石(2MgO·2Al2O3·5SiO2)易于加工成形、机械强度高、价格低廉、热膨胀性质与分子筛相近被广泛用于整体式催化剂的载体。在分子筛/堇青石整体式催化剂的制备中，原位水热合成是一种非常简单可行的方法。但仍然存在分子筛负载量低、制备过程条件苛刻、堇青石表面上ZSM-5分子筛的覆盖不均匀，ZSM-5分子筛与载体结合的牢固度的考察不够深入等问题。

本论文从deNOx催化剂的实际应用出发，利用水热合成技术，通过原位和预涂覆溶胶法使分子筛牢固负载于堇青石蜂窝陶瓷载体上，并模拟实际柴油机尾气的操作条件，评价了整体催化剂的deNOx性能。

对堇青石蜂窝陶瓷载体上合成的ZSM-5分子筛负载量和牢固度测试结果表明：在不使用模板剂的条件下，当晶化时间为24~60h时，超声波处理60min后，空白堇青石质量增加为2.51~13.89%；经过预涂覆溶胶晶化时间24~60h，超声波处理60min后，空白堇青石质量增加为4.32~17.02%；表明堇青石表面分子筛具有一定的负载量和牢固度。

将制得的ZSM-5/堇青石分别以离子交换法和浸渍法制备了Cu-ZSM-5/

堇青石整体催化剂，考察了在模拟柴油机尾气气氛条件下的deNOx催化性能。NH3-SCR测试结果证明：离子交换法制备的催化剂比浸渍法制备的催化剂具有较高的NO转化率和较宽NO转换温度窗口，在温度为550-750K的区间内，NO转化率接近100%，催化活性随着反应气中氧浓度的增大和空速的增大而略有降低。C3H8-SCR评价结果表明：温度在725~895K之间，C3H8的转化率达到了100%，NO的转化率较低，在测试温度为575~895K的区间内，最高转化率仅为50%左右。水蒸气气氛，对C3H8的转化，几乎没有影响，但对NO的转化，有强烈地抑制作用，其最高转化率不足40%。

关键词：柴油机尾气，原位合成，deNOx催化剂，选择性催化还原

STUDY OF THE MONOLITHIC Cu-ZSM-5/CORDIERITE

CATALYST FOR DIESEL EXHAUST GAS PURIFICATION

ABSTRACT

Three-Way-Catalysts(TWC) is an effective way to abate CO, HC and NOx in the traffic flue gas simultaneously. However，this type of catalysts is only effective in the narrow range of air to fuel ratio (adjacent to l4.7). Combustion of fuel in the presence of excess oxygen is not only an effective way to improve the fuel utilizing efficiency, but also can decrease the emission of pollutants. However, TWC catalysts exhibit low activity for NOx reduction in these conditions. Metal supported zeolites are considered as one of the promising candidate in this field. Zeolite catalysts must be loaded onto carriers in order to reduce vehicle exhaust resistance. Especially, cordierite (2MgO·2Al2O3·5SiO2) are widely used due to the superior hydrothermal stability, cheap price, plasticity, good washcoat adherence and compatibility with washcoat. In situ hydrothermal synthesis technology is a very simple and workable method in the process of catalyst preparation. The study of in situ synthesis indicates that ZSM-5 can be loaded on the cordierite surface to increase the specific surface area. In spite of meaningful results being obtained, there are some problems to be overcome. For example, the combining properties of molecular sieve layer and carrier, uniformity of the distribution of molecular sieve, the amount of molecular sieve on supports, which are crucial for the application of the monolithic catalysts.

In the present thesis, focusing on real applications, zeolites were tightly supported onto ceramic honeycombs by in-situ synthesis and pre-coating sol synthesis. The performance of Cu-ZSM-5/cordierite monolithic catalysts in the abatement of NO in simulated diesel-engine exhaust conditions was explored. Both the weight percentage of monoliths coated and adhesion degree of

ZSM-5 onto cordierite were tested. When crystallization time is extended to 60h from 24h and after the monoliths are treated 60 minutes with ultrosonic, the results indicate that the weight of blank cordierite without employing any structuring templates is increased from 2.51% to 13.89% in situ synthesized ZSM-5/cordierite. For the ZSM-5/cordierite made by pre-coating sol synthesis, the weight of blank cordierite is increased from 4.32% to 17.02% with crystallization time of 24h to 60h after the monoliths are treated 60 minutes with ultrosonic.

On the basis of the above synthesis, Cu-ZSM-5/cordierite monolithic catalyst is prepared by ion-exchange and impregnation method and applied for the selective catalytic reduction (SCR) of NOx using a simulated diesel exhaust. For the NH3-SCR process, Cu-ZSM-5/cordierite catalyst obtained by ion-exchange methods shows a wide temperature window of maximum activity than those of catalyst prepared only by impregnation method. The conversion rate is closed 100% in the temperature range of 550～750 K. The NO conversion rate will be down with the increase of the GHSV and the oxygen concentration in ambient gases. For the C3H8-SCR process, when the temperature is in the range of 725~895K, the C3H8 conversion rate is almost 100%. But the conversion rate of NO is low, and the highest conversion rate is 50%. The addition of water vapor in the reaction gases has unobvious effect on the conversion of C3H8, but greatly reduces the conversion of NO and the highest conversion rate is less than 40%.

KEY WORDS: diesel exhaust，in-situ synthesis，de-NOx catalyst, selective

catalytic reduction

第一章 文献综述

1.1 课题背景及意义

随着现代化交通系统的发展和汽车数量的增加，柴油机的使用也越来越多。柴油机主要应用在大功率机械，包括公交、大卡车、建筑采矿设备等。近年来，柴油机因其经济型、可靠性、耐久性以及强劲的动力，也逐渐应用到轻型汽车中。柴油机与汽油机相比具有更 …… 此处隐藏：16087字，全部文档内容请下载后查看。喜欢就下载吧 ……