CO2加氢制甲醇的Cu纳米粒子/ZnO单晶模型催化界面研究

In the past decades, global warming caused by increasing atmospheric CO2 concentration and the depletion of fossil fuels have been becoming the focus of much attention by scientists and governmental agencies. Catalytic conversion of CO2 has a positive impact on these 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 methanol catalysts for syngas hydrogenation, which contained Cu and ZnO as the main components together with alumina support and different modifiers. 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. We have previously reported that significant shape effect and heterojunction modulation of ZnO on the interaction with copper in the synthesis of methanol from CO2 hydrogenation. The interfacial electron transfer from ZnO to Cu is quite important to the improvement of methanol selectivity of the model catalysts derived from the phisical mixtures of Cu nanoparticles and ZnO nanocrystals.In this proposal, we planned to synthesize a series of ZnO nanocrystals and Cu nanoparticles with different surface structures and properties. Thus, we can obtain various model interfaces of Cu/ZnO catalysts by physically mixing the both components. The influence of these model catalyst surfaces or interfaces on their chemical adsorption behavior and catalytic properties for hydrogenation of CO2 to methanol will be systematically investigated. We believe that the inter-relationships between materials interaction, electronic characteristics and catalytic performance provide a new clue to lead to rational catalyst design for this important green process.

因与环境和能源问题密切相关，CO2加氢制甲醇技术一直受到广泛关注，而催化剂是制约其工业化的关键因素之一。目前，以Cu/ZnO催化剂的研究最多，但至今就其各组分的界面相互作用仍有争议，对于各组分微观结构不同所产生的界面性质变化，以及由此引起的催化与反应动力学性质变化，认识仍有限。最近，我们采用不同ZnO纳米单晶负载相同的Cu纳米粒子，发现Cu/ZnO界面相互作用较强（ZnO向Cu的界面电子转移）时，催化CO2加氢的甲醇选择性较高。本项目拟建立ZnO单晶和Cu纳米粒子的制备与改性方法，实现对两者表面结构性质的有效调控。通过ZnO单晶负载Cu纳米粒子来构建模型催化界面，系统研究其界面结构性质的变化，及其对表面吸附过程和目标反应催化性能的影响机制。通过本项目的实施，可丰富对此类金属-氧化物催化剂界面相互作用的认识，加深对纳米催化剂表面效应的理解，也能为高效催化剂的设计合成提供基础数据。

固体催化剂的微观表面或界面是化学反应发生的真正场所，其结构性质与催化性能密切相关。但商品化的催化剂各组分相互混杂，难以严格区分其界面结构。采用形状与尺寸较为单一的氧化物纳米单晶与金属纳米粒子共同构建纳米尺度模型催化剂，是研究金属-氧化物复合催化剂界面结构性质与其化学吸附行为、催化性能相关性的有效方法。Cu-ZnO体系是合成气制甲醇工业用催化剂，也是CO2加氢制甲醇这一重要反应目前研究最多的催化剂品种。本项目系统研究了不同长径比氧化锌纳米单晶的制备方法，，深入探讨暴露晶面的不同对氧化锌负载铜基催化剂的表面物化性质、化学吸附行为及CO2加氢催化性能的影响。采用异质结改性的方法对棒状氧化锌纳米单晶进行修饰，使之甲醇选择性得以大幅提高。考察了多种金属纳米粒子的可控制备技术，并将其应用于铜、钯等纳米催化剂的合成。同时，优化催化剂结构，获得一种基于金属Pd/ZnO催化剂。将氧化物纳米单晶负载金属纳米粒子构建模型催化界面的方法推广应用于CO2加氢的Pd/Ga2O3体系和甘油氢解的钯/氧化铁体系获得成功，进一步验证了金属与载体界面相互作用对其化学吸附行为和催化性能的重要性。本项目发表SCI研究论文3篇（标注基金资助），另有三篇正在整理之中。2013年基于本项目的后续研究获得国家自然科学基金面上项目资助（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，21373153）。项目执行过程共培养博士1人，硕博连读研究生4人，硕士生2人。