原位揭示负载型银催化剂生成过程及其结构调控

Supported catalyst is the most important catalyst in the petroleum refining and petrochemical engineering fields. When the supported catalysts are prepared by the impregnation method, the thermal treatment induces complex physical and chemical reactions. We take the preparation of silver catalysts used for ethylene epoxidation as an example. The thermal treatment firstly leads to the crystallization of silver salt followed by the themolysis of the salts forming silver nanoparticles on the surface of the support. The thermal treatment determines the size and distribution of silver particles as well as the internal structures of silver particles, which dominates the efficiency and selectivity of silver catalysts. However, the formation process of silver particles during the thermal treatment is not well studied, which limits our ability in designing new catalysts with advanced properties. In this proposal, we plan to use in-situ techniques, such as environmental scanning electron microscopes, to disclose the physical and chemical changes of silver salts during the thermal activation, to reveal the unknown dynamic phenomena in this process. Then we attempt to discover the influence of thermal parameters on the distribution and structure of silver catalysts, figuring out the mechanism dominating the structures of silver catalysts. Under the guidance of the proposed mechanism, silver catalysts with suitable size, even distribution and controlled structure are expected to be synthesized. The acquirements in this project are expected to improve our ability in designing and developing new supported catalysts with high efficiency and high selectivity.

负载型催化剂是石油炼制和石油化工领域最重要的一类催化剂，在浸渍法制备负载型催化剂过程中，热处理活化工艺引发了复杂的物理和化学变化；以乙烯环氧化制备环氧乙烷所用的负载型银催化剂为例，制备过程中的热处理工艺即引发了银盐干燥析出，又导致了银盐的分解以及银纳米团簇的生成，但是这些复杂变化过程对催化剂结构的影响还不清楚，这为催化剂的制备带来了很大的不确定性。本项目拟采用环境扫描电镜等技术原位观察银盐的干燥热解过程，并通过多种分析手段，验证观察结果，以期揭示热处理时银催化剂的动态生成过程；在正确理解这一过程的基础上，研究热处理工艺对催化剂结构的调控作用和规律，探讨热处理过程中银盐的反应和扩散对催化剂结构的影响，明确热处理工艺对负载型催化剂结构的调控机制；在新机制指导下，合理设计实验，制备出大小适中分布均匀结构可控的负载型银催化剂，为高效高选择性负载型催化剂的开发提供理论指导。

负载型催化剂是石油炼制和石油化工领域最重要的一类催化剂，在浸渍法制备负载型催化剂过程中，热处理活化工艺引发了复杂的物理和化学变化，但是这些复杂变化过程对催化剂结构的影响还不清楚，这为催化剂的制备带来了很大的不确定性。本项目通过离线和原位电镜技术研究了硝酸银热解生成银催化剂颗粒的过程，主要发现如下：.（1）热处理过程中，反应原料在载体表面的熔解会导致原料的流动及在表面的重新分布，一般低洼表面富集反应原料，继续升温，金属催化剂从熔融液体中析出，因此液相的生成对于催化剂颗粒的分布具有重要的影响。.（2）硝酸银的热解过程中，先生成氧化银，氧化银再分解生成银纳米颗粒。金属颗粒的生成温度低于文献中的反应原料的分解温度，如文献中报道，氧化银分解为银的温度是300℃，但是在原位透射电镜中发现220℃银颗粒开始析出，后期继续升温，银颗粒长大。.（3）热解温度过高或热解时间过长会导致银纳米颗粒的熟化。. 发表SCI文章12篇，包括化工类主流期刊CES，CEJ，IECR和晶体生长类主流期刊Crystal Growth & Design 和CrystEngComm以及化学材料类主流期刊Nano Research和Scientific Reports；文章列表见报告正文。培养博士生2名，硕士生2名，本科毕设学生5人。