RhOx/CeO2催化剂的表界面结构及其催化作用的理论与实验研究

Theoretical investigation of the effects of catalyst treatment conditions, particle sizes of active component and support structures on the catalyst structures is of great significance for the theoretical design of catalysts. However, density functional theory is difficult to calculate the practical catalyst model for the low efficiency; meanwhile the catalyst structure information obtained by the ex-situ TEM/XPS at the ultra high vaccum is greatly different from those in the practical conditions. This reduces the comparability of theoretical predictions and experimental results. To solve these problems, the RhOx/CeO2 catalysts with an important industrial application are chosen in the present work. Using the newly developed theoretical method with high efficiency and the in-situ ambient pressure TEM/XPS techniques, the structures of RhOx/CeO2 catalysts with different O/Rh ratios, RhOx particle sizes and ceria surfaces are systematically optimized. Correspondingly, the quantitative correlations among the treatment atmosphere, particle sizes of RhOx, ceria surfaces and the structures of RhOx/CeO2 are established by combining with the molecular dynamics simulation and catalyst characterization of in-situ ambient pressure TEM/XPS. Based on the adsorption and reaction behaviors of probe molecules on RhOx, CeO2 and their interface, the active sites and reaction mechanism are deduced by combining with the experimental results. This work provides important information for the development of catalysts with high efficiency at the relatively low temperature. Furthermore, the method in this work is widely suitable for the catalyst study of metal and oxide nanoparticles on supports. This work will also provide a research method and data accumulation for catalytic research from the trial-and-error mode to theoretical design at the molecular level.

理论研究催化剂处理条件、活性组分粒子尺寸、载体结构等因素对催化剂表界面结构的影响对催化剂理性设计具有重要意义。目前，由于效率问题，密度泛函理论方法难于计算与实际催化剂尺寸匹配的模型；同时非原位、高真空TEM/XPS表征结果与催化剂真实信息差别较大，导致理论与实验结果可比性降低。本项目选择重要应用价值的RhOx/CeO2体系，将最新高效理论方法与原位近常压TEM/XPS表征结合，通过计算不同O/Rh比、RhOx尺寸在载体不同晶面上的结构，结合分子动力学模拟及原位近常压TEM/XPS表征，建立气氛-RhOx尺寸-载体晶面-催化剂结构间的定量关系。通过计算探针分子在RhOx、载体及界面的吸附反应行为，结合实验结果，获取催化剂的活性中心与反应机理，为开发低温高效催化剂提供依据。本项目的研究方法对金属及氧化物纳米粒子负载型催化剂有普适性，为催化研究从炒菜模式走向理性设计进行研究方法的探索与数据积累。

项目立项以来，负责人按照项目计划有序开展相关工作。通过全局优化算法系统计算了不同 O/Rh比的RhOx团簇的最优结构，在此基础上系统计算了CO、O2、H2的吸附与反应行为，建立了CO氧化反应的粒径-气氛-结构的定量关系。通过系统研究了Rh2O3不同终端表面在不同O2、H2分压、不同温度下的吸附结构，获得了接近真实反应条件下的RhOx表面结构，建立了催化剂不同处理条件与RhOx催化剂结构间的定量关系。通过制备不同Rh负载量Rh2O3/CeO2、Rh2O3/SiO2催化剂，系统研究了催化剂处理气氛对其结构与CO氧化反应性能的影响。理论计算与实验相结合，发现部分氧化的RhOx/CeO2催化剂的活性最高，建立了气氛-Rh/O-催化剂性能的定量关系。通过理论与实验相结合，系统研究含水率对Pt/α-Fe2O3催化剂CO氧化性能的影响，开发了较高与较宽水浓度范围内具有高CO氧化活性的催化剂。将该研究思路与方法用于电催化水氧化制双氧水，开发了高活性（较文献高约50倍）、高选择性（法拉第效率93%）、高稳定性的锡基催化剂。通过发展用于计算自由分子、体相材料、表面吸附分子的拉曼光谱脚本程序Simulated Raman Spectrum (SRS)，系统计算了不同化学势下铈基催化剂氧缺陷拉曼光谱、表面吸附物种与铈基催化剂表面精细结构的拉曼光谱、铈基固溶体复合物叠加拉曼光谱，从分子水平解析了铈基催化剂氧空位、催化剂表面精细结构、表面吸附物种、固溶体复合氧化物拉曼光谱产生的微观机制，解决了相关问题近30多年的争议。通过理论与实验相结合，提出了定量获取不同活性位表面、位点在光催化、热催化反应中的催化作用和活性的普适性方法，定量测定了Pd金属催化剂不同表面原子(100与111)、不同棱(100与111)的光催化固氮反应活性的催化活性。通过本项目的实施，从微观电子角度解释了RhOx-CeO2间电子相互作用及其对催化反应、拉曼光谱的影响，为设计开发低温高效铈基催化剂提供了重要理论与实验依据。