金属/二氧化铈多相催化剂中金属与载体电子相互作用和催化应用的研究

During the past decades, the extensive research has been focused on the fundamental understandings of the metal-support interaction of heterogeneous catalysts with the aims of the high catalytic activity, selectivity and stability for many important catalytic reactions. However, the investigations still face to many challenges: 1) Serious unfairness of the surface properties of metals and supports of heterogeneous catalysts synthesized by various methods. The surface properties of metals or supports including morphology, surface area, size, crystal planes in the catalysts synthesized by different methods, which can induce very vast catalytic performance. Unfortunately, they are ignored in the state-of-the-art research. While, the catalytic performance is attributed to metal-support interactions in generalities. 2) Molecules or ions during catalyst synthesis can be adsorbed on the surface of metals, supports and their interfaces, which can modify their electronic structures of the catalytic active sites. Such a modulation was seldom considered in the literatures. However, they indeed affect the catalytic performance. 3) Pre-treatments on catalysts or chemical environments also affect the surface properties of metals and supports as well as their interfaces. Thus, the electronic structures of the surface catalytic centers can be significantly modulated. Even, the active sites could be completely altered during those processes. Inspired by the recent progress and remained challenges, herein, the metal/CeO2 as the model catalysts and probe reactions (e.g., CO oxidation, hydrogenation of alkenes) are employed to understand the metal-support interaction. Based on our previous investigations, the photo-assisted metal deposition and electroless chemical deposition are developed to synthesize the metal/CeO2 catalysts with the controllability on the metal compositions, sizes, dispersions, morphology and surface areas and the surface absorption of molecules/ions. They provide platforms to explore the electronic metal-support interaction. Various techniques including X-ray photoelectron spectroscopy, FTIR and synchrotron radiation will be employed to monitor the evolutions of metal, support and their interactions including the charge exchange and phases transformation under the specific conditions. Combining the DFT calculations, the comprehensive understandings on the metal-support interactions are expected. It will help to understand the modulations of foreign molecules/ions, pre-treatments and catalytic environments on the metal-support interaction and recognize the catalytic mechanism.

金属-载体相互作用可有效调控催化剂表面活性位点的电子结构并影响反应的活性、选择性及稳定性。但当前研究存在如下问题：1)研究基础的不公平性。不同方法得到的催化剂中载体和金属的表面性质各不相同，无法将催化差异性简单归结为协同效应。2) 忽略催化剂制备中分子或离子吸附对活性中心的调控。3) 催化剂前处理或反应气氛对二者表面调控不明。本项目拟在课题组前期金属/CeO2工作基础上，展开对分子/离子吸附、催化剂预处理与反应气氛等对金属/ CeO2相互作用的系统研究。首先利用光辅助和无电子化学沉积法将金属可控沉积在CeO2上。再通过探针反应研究不同分子或离子、前处理与反应气氛对金属、CeO2和界面的电子结构与化学环境影响。进一步利用原位实验揭示二者在反应中如何相互作用和动态演变，深入理解反应机理。在此基础上，预言并验证金属/CeO2活性中心的调控和实现催化剂的优化。

项目采取“可控调节催化剂表面性质-构筑新活性位点-实现物种在催化剂表面竞争性吸附-理论计算”的研究策略，调控基于二氧化铈催化剂表面活性位的电子和空间结构，强化催化剂设计理念，构筑了一些重要化工反应的新路径，并将相应的催化理论拓展到其他催化体系。创新点有如下四点。1) 利用二氧化铈缺陷构筑表面受阻路易斯酸碱对FLP并提出构建该位点的三要素：表面独立路易斯酸和路易斯碱位点；酸碱空间距离与电子结构的双重亚纳米尺度匹配。FLP有效活化氢气、二氧化碳、水与醇，并实现了不饱和化合物加氢、烯烃与二氧化碳合成碳酸脂、低温甲醇湿法重整制氢和生物质氢转移加氢等反应。(2) 强化金属活性中心与载体相互作用，构筑双活性位点，实现了加氢催化剂的高活性、高选择性和高稳定性。不饱和化合物与载体上第二活性位点之间的强相互作用使其选择性吸附在载体；而金属作为第一活性位点仅用于吸附活化氢气，通过氢溢流实现底物选择性加氢。该策略成功打破了不饱和化合物加氢过程中Sabatier原理的限制，提高了催化加氢性能。采用金属尺寸效应、物理阻断和表面毒化等方法，成功应用到芳香硝基化合物、喹啉、吲哚、卤代芳香化合物的选择性加氢反应。(3) 调控二氧化铈表面性质，实现了界面处生物分子吸附强度可控，促发了其新的仿生催化活性。首次报道二氧化铈仿光裂解酶的仿生催化性能，逆转了紫外线所带来的皮肤损伤。同时也大幅度提高其模拟氧化酶、SOD酶、磷酸酯酶等催化性能。(4) 铈作为辅助催化剂调控电催化剂表面质子吸附强弱，提高电分解水催化剂的活性与稳定性。成功将热催化加氢中的氢溢流效应用于金属负载型电催化制氢反应中来。金属与载体之间功函差绝对值被认证为激发氢溢流的描述符与内因。项目在JACS, Nat Commun, Chem等期刊上发表43篇论文，授权专利3项，申请专利6项，受邀在ACS Catal, Nano Res, 物理化学快报等上撰写综述，受邀在全国催化学术会议、全国青年催化学术会议等国内外学术会议做学术报告。