氧化钛负载贵金属催化剂的金属-载体强相互作用原位动态研究

Strong metal-support interaction (SMSI) has long been known to significantly mediate the performance of TiO2-supported noble metal catalysts, but in-depth insights into its chemical nature is still quite limited. This is mainly because of the difficulty in constructing well-regulated and uniform metal-support interfacial structure from a catalyst preparation point of view and the inaccessibility of characterizing the entire catalyst particle by spectroscopic and visualizing techniques at elevated temperatures and under reactive atmospheres. The rapid progress in nanocatalysis, during the past three decades, now enables the precise fabrication of relatively uniform metal-oxide interface through carefully tuning the size and shape of metal and oxide particles at nanometer level; while the revolutionary advance in visualizing and spectroscopic characterization techniques allows in situ and dynamic imaging of the structural and electronic features of the working catalysts, at least partially. ..This project is subjected to elaborate the fundamental understanding of the strong metal-support interaction in TiO2-supported Au、Pd、Pt and Ir catalysts, mainly covering the construction of metal-oxide interfaces and the in situ characterization of the catalysts at functionalities. It starts with the fabrication of catalysts with tunable size and shape at the nanometer level for both metal and TiO2, and then focus on in situ characterizations of the dynamic behavior of the catalysts under alternatively reductive and oxidative atmospheres at elevated temperatures, by using mainly high-resolution synchrotron radiation and aberration-corrected environmental transmission electron microscopy. In situ synchrotron radiation X-ray adsorption spectroscopy (XAFS), will be used to monitor the evolution of the chemical and electronic properties of the working conditions. Advanced transmission electron microscopy, including image-corrected environmental transmission electron microscopy (ETEM) and probe-corrected scanning transmission electron microscopy (STEM) equipped with in situ high temperature atmospheric holder (also called nanoreactor), will be used to directly observe the dynamic variations in size, shape, and interfacial structure of the catalysts at working conditions. Their combination, together with other routine characterization methods and theoretical calculations, would provide a full picture of the geometric and electronic structures of the working catalysts, and consequently the detailed mechanism of the SMSI phenomenon that would be correlated with the catalytic performance for the oxidation reactions of C=O and hydrogenation reaction of C=C bonds.

金属-载体强相互作用(Strong Metal-Support Interaction, SMSI)是氧化物负载金属催化剂的关键特征，但是目前对这种强相互作用机制仍然缺乏深入了解。主要原因在于负载型催化剂金属粒子尺寸的不均一性、氧化物表面结构的多样性、表征技术在气氛和温度下分辨率和灵敏度的局限性。本项目针对SMSI机理研究，选择具有代表性的TiO2负载的Au、Pd、Pt、Ir催化剂体系，在纳米尺度上调控金属粒子尺寸和氧化钛表面结构(形貌、晶相)，构建均一的金属-氧化钛界面结构；利用原位透射电子显微镜技术，依托上海光源“X射线吸收精细结构谱学(XAFS)”线站，考察温度、气氛和反应条件下金属-载体相互作用的空间/电子效应的动态变化；结合C=O氧化、C=C加氢反应性能测试，在原子层次上阐明氧化钛负载贵金属催化剂的SMSI机制，以及相应的金属-载体界面原子结构与催化反应性能的内在关联。

金属-载体强相互作用是负载型催化剂的典型特征，对其物理和化学机制的研究，不仅是理解催化作用的关键，也是研制高效催化剂的科学基础。本项目针对具有金属-氧化物强相互作用的氧化物负载贵金属界面调控及原位动态表征开展研究，发展了用于贵金属粒子(Pt、Au、Pd) 制备的液相还原技术，优化了不同形貌的氧化钛的制备条件及技术；并发展了金属-氧化物组装技术，成功实现了Pt/TiO2、Au/MoC等催化剂体系的界面调控。发展了原位动态表征技术，对Pt/TiO2和Au/MoC等具有强金属-载体相互作用的催化剂体系，联合采用原位X射线同步辐射吸收光谱(XAFS)、球差校正的环境(扫描)透射电子显微镜(ETEM / ESTEM)及原位红外（IR）、X射线光电子能谱(XPS)等技术，在原子尺度解析了Pt/TiO2、Au/MoC催化剂在不同温度及气氛(H2、CH4/H2)、反应条件下的界面结构及金属载体强相互作用机制，揭示了氧化钛上Pt的再分散机制，为通过调控金属-氧化物相互作用方式研制高活性催化剂提供了实验和理论基础，深化了对金属-载体强相互作用化学机制的认知。在上述研究过程中，项目负责人在the Journal of Physical Chemistry C、the Journal of Physical Chemistry Letter等期刊上发表(共同)通讯作者学术论文2篇；另有2篇相关论文已投稿，2篇整理待发表。申请发明专利一项；参加第20界全国催化大会并做主旨报告；参加第18界全国青年催化大会并做邀请报告；协助培养博士研究生3名(已毕业2名)。