ZnO纳米单晶极性面调控及其负载铜基催化剂的制备、表面性质与CO2加氢制甲醇催化性能研究

In the past decades, catalytic conversion of CO2 has a positive impact on the important environmental and energy issues. In particular, the hydrogenation of CO2 to methanol looks very attractive due to its position as a high energy density liquid fuel and key chemical intermediate. The majority research on catalytic studies for CO2 hydrogenation has been using modified industrial Cu-ZnO catalysts. But up to now, the exploitation of the catalyst is slow due to the lack of knowledge on both hydrogenation reactions and the fundamental understanding of important materials interaction(s) in catalyst formulation. The invetigations by using surface science technique and theoretical caculation simulation revealed that the surface structure and property of ZnO single crystal is important for its chemical adsorption behavior and the structure of deposited Cu nanoparticles. But the simple and clean single crystals used for these studies are always inactive compared with real catalysts. Recently, we have reported that metal nanoparticles supported on oxide nanocrytals can be utilized as nano-scale model catalysts, whose catalytic properties can be tested directly and affected markedly by the exposed surface of the support.In this proposal, we planned to synthesize a series of ZnO nanocrystals, of which the exposed polar surface proportion can be controlled. Thus, we can investigate the relationship between the support's surface polarity and the chemical adsorption behavior as well as the growing model of deposited Cu nanoparticles on its surface. Additionally, the similar Cu nanoparticles will be supported on different ZnO nanocrytals to prepare nano-scale model catalysts. The influence of the nanocrystal surface on the chemical adsorption behavior and catalytic properties of these model catalysts will be systematically investigated for the hydrogenation of CO2 to methanol. We believe that the relationships between surface properties, materials interaction and catalytic performance provide a new clue to rational catalyst design for this important green process.

因与环境和能源问题密切相关，CO2加氢制甲醇技术倍受青睐，而催化剂是制约其工业化的关键因素之一。目前Cu-ZnO催化剂研究最多，但催化反应机理与金属-载体相互作用仍有较大争议。近年来表面科学与理论研究发现ZnO单晶表面结构性质直接影响其吸附行为和沉积金属结构，但所用模型样品结构简单，并不具催化活性。最近我们发现氧化物纳米单晶负载金属纳米粒子可构建更接近真实体系的纳米尺度模型催化剂，其性能与载体暴露晶面密切相关。因此本项目拟详细考察不同长径比棒状ZnO纳米单晶的制备方法，调节其暴露极性面的多寡。同时系统研究ZnO纳米单晶表面极性对其化学吸附、以及液相中表面铜沉积生长的影响。进而采用不同的ZnO纳米单晶负载相同的铜纳米粒子制备模型催化剂，系统研究载体表面结构与性质对催化剂化学吸附和CO2加氢催化性能的影响规律。本项目的实施有望丰富对金属-氧化物相互作用的认识，为高效催化剂开发提供基础数据。

CO2加氢制甲醇倍受关注，但目前难以工业化的原因在于廉价绿色氢源的获取和高效催化剂的研制。本项目通过采用ZnO纳米单晶负载金属Cu纳米粒子构建模型催化剂，开展催化剂各组分构效关系的基础研究，共发表标注基金资助SCI论文9篇（其中影响因子4.0以上的4篇，一区论文2篇）。主要进展如下：.（1）.模型催化界面研究。发现盘状氧化锌与铜纳米粒子之间存在较强界面相互作用，直接导致含盘状氧化锌模型催化剂甲醇选择性远高于含棒状体系，归因于界面处ZnO向Cu的电子转移。发现半导体异质结构可调控材料电子性质，Cu/CdSe-ZnO催化剂其甲醇选择性随CdSe含量的增加而增大，进一步验证构建模型催化界面研究构效关系的普适性。.（2）.氧化锌负载金属（Cu或Pd）催化剂载体效应研究。发现氧化锌载体中掺杂Ga3+离子形成ZnGa2O4-ZnO异质结，负载金属铜纳米粒子后在界面发生电子相互作用，导致生成CuZn纳米合金相，是CO2加氢的催化活性中心。而采用CdSe-ZnO异质结负载Pd催化剂，则是在界面处生成Pd@Zn纳米合金。采用无毒半导体材料g-C3N4修饰ZnO亦可制备优良CO2加氢催化剂。.（3）.纳米金属催化剂的控制合成方法与应用基础研究。采用有机半导体负载纳米金属催化剂用于光-电耦合催化，证实导电聚合物-金属界面电子相互作用对催化活性影响显著，并应用于CO2的电催化还原和可见光催化有机物降解。.（4）.催化剂金属活性组分（Cu、Pd）的结构调控及其构效关系研究。系统研究了内核合金组分比例变化对核壳结构纳米催化剂化学吸附行为及催化性能的影响规律，还探究了氧化锌负载Ag@Pd核壳结构催化剂内核金属对钯基催化剂的调控。系统研究CO2加氢制甲醇钯修饰Cu-ZnO催化剂氢溢流对铜活性中心的促进作用，发现高度还原性的铜活性位点可能是CO2加氢制甲醇的真正活性位。.本项目涉及对金属-载体的界面电子相互作用的深入理解，这对于CO2加氢用高效催化剂的研制具有重要意义。