huaxue

中南民族大学硕士学位论文

铂钯双金属纳米催化剂的制备及催化活性研究

姓名：王然申请学位级别：硕士专业：物理化学指导教师：何宝林

20060605

huaxue

中南民族大学硕士学位论文

摘 要

双金属纳米颗粒就是包括两种不同的金属原子，与单金属相比较，双金属纳米颗粒具有以下一些特性：①有助于研究不同金属合金形成过程，为其提供模型；②改变双金属的组成，可以得到与单金属颗粒不同的性质，例如添加第二种金属元素可以改变单金属纳米颗粒的催化活性、选择性和抗失活性。③双金属纳米颗粒具有特殊结构，例如，核壳结构、簇簇结构、分离或任意结构。④改善合成工艺可以节约贵金属材料。

本文利用化学还原法合成了由聚乙烯吡咯烷酮(PVP)稳定的Pd、Pt单金属纳米颗粒，在单金属纳米催化剂的基础上采用分步还原的方法分别合成了PVP-PdxsPty和PVP-PtxsPdy双金属纳米胶体，采用同时还原的方法合成了PVP-Pd0.5Pt0.5双金属纳米胶体，所得产物具有粒径小、分布窄、在室温下可稳定地储存数月而不沉淀的性质。并用紫外可见光谱(UV-vis)、透射电子显微镜(TEM)及X-射线衍射(XRD)对其进行了表征。结果发现采用不同步骤制备的钯铂双金属纳米催化剂具有不同的颗粒结构：以纳米Pt为晶种制备的PVP-PtxsPdy 具有核壳结构，即Pt为核Pd为壳；以纳米Pd为晶种制备的PVP-PdxsPty的颗粒结构比较复杂，颗粒表面可能是Pd、Pt的合金相，颗粒内部可能是Pt或Pd；同时还原法制备的 PVP-Pd0.5Pt0.5 也具有核壳结构，即Pt为核Pd为壳。以环己烯为原料，甲醇为介质，检测了纳米Pd、Pt及采用不同方法合成的一系列纳米钯铂双金属催化剂均相催化氢化环己烯的催化活性。结果表明，颗粒结构不同的催化剂，对环己烯具有不同的催化活性，在不同pH值条件下同一催化剂也表现出不同的催化活性，因此钯铂双金属纳米催化即在催化环己烯时体系的酸度是一个不可忽视的因素。在催化剂使用寿命的实验中，发现钯铂双金属纳米催化剂的使用寿命比单金属钯、铂催化剂的使用寿命要长，催化活性降低速率慢。

关键词：钯,铂；纳米；双金属催化剂；核壳结构；环己烯；催化氢化

huaxue

铂钯双金属纳米催化剂的制备及催化活性研究

ABSTRACT

As the name implies, bimetallic nanoparticles are metallic entities comprising atoms of two different metallic elements. Compared with monometallic nanoparticles, bimetallic nanoparticles are of special interest for several reasons. First, they may serve as models for studying the formation of different alloys. Second, these bimetallic particles may have more varied properties than monometallic particles as various combinations are possible. It is well established that the catalytic properties of the monometallic nanoparticles, including activity, selectivity or resistance to deactivation, can be altered by the addition of the second metal. Third, bimetallic particles could have particular structures not seen in bulk alloys, such as core-shell, cluster-in-cluster, separate, random structures, etc. Fourth, it is possible to save the precious metals by optimizing the synthesis conditions.

PVP-protected Pd nanoparticles and Pt nanoparticles were synthesized in methanol/water(1/1,v/v) by the method of chemical reduction. PVP-stabilized Pd/Pt colloids with molar ratio of PVP: total metal =40: (x+y) were prepared through simultaneous or stepwise methanol reduction. On addition of the 10 mL 0.1 M methanolic NaOH into the reducing systems. The colloids prepared have small particle size with narrow size distribution.They are stable under ambient condition for months. The nanoparticles were characterized by UV-vis, TEM, and XRD. The possibility of the bimetallic nanoparticles prepared by different method has different structures. For instance, PVP-PtxsPdy and PVP-Pd0.5Pt0.5 may have core-shell structure with Pd as the shell and Pt as the core. And PVP-PdxsPty may has an alloy phase of Pd and Pt on the surface structure .We test the catalytic activity of these bimetallic nanoparticles by hydrogenation of cyclohexene .We can deduct from the result of the hydrogenation that PVP-PtxsPdy and PVP-Pd0.5Pt0.5 with a core(Pt)-shell(Pd) structure have higher catalytic activity than Pt monometallic nanoparticles. In addition , changes in pH was also found to have significant effects on the catalytic activity. But PVP-PdxsPty has very low catalystic activity on hydrogenation of cyclohexene. We found that service life of bimetallic catalysts is higher than monometallic catalysts.

Keywords : Pd and Pt; nanometer; bimetallic nanoparticles; core-shell structure;

cyclohexene; hydrogenation

huaxue

中南民族大学 学位论文原创性声明

本人郑重声明：所呈交的论文是本人在导师的指导下独立进行研究所取得的研究成果。除了文中特别加以标注引用的内容外，本论文不包含任何其他个人或集体已经发表或撰写的成果作品。对本文的研究做出重要贡献的个人和集体，均已在文中以明确方式标明。本人完全意识到本声明的法律后果由本人承担。

作者签名：

日期： 年 月 日

学位论文版权使用授权书

本学位论文作者完全了解学校有关保留、使用学位论文的规定，同意学校保留并向国家有关部门或机构送交论文的复印件和电子版，允许论文被查阅和借阅。本人授权中南民族大学可以将本学位论文的全部或部分内容编入有关数据库进 …… 此处隐藏：12553字，全部文档内容请下载后查看。喜欢就下载吧 ……