氟化的类水滑石衍生高分散铜基催化剂的构筑及其CO2加氢行为研究

Catalytic conversion of CO2 to methanol is an important route for CO2 chemical utilization. Low CO2 conversion and methanol selectivity as well as the inhibitive effect of water for the catalyst deactivation are the major problems that yet to be circumvented. Our previous work indicated that the CO2 conversion mainly depended on the Cu dispersion and the CH3OH selectivity was related to the proportion of strongly basic sites. Additionally, for the Cu-based catalysts derived from hydrotalcite-like (HTl) compounds, the Cu dispersion increased with the increase of the dispersion of platelets and the surface basicity of catalysts could be improved with introduction of fluorine ions. The present proposal intends to synthesize the precursors with highly-dispersed platelet crystals by tailoring the structure and morphology of the hydrotalcite-like compounds. Simultaneously, the fluorine ions were directly introduced into HTl layers. Then, the fluorine-modified catalysts with well layered structure will be obtained by heating the fluorinated precursors under appropriate conditions and tested for the methanol synthesis from CO2 hydrogenation. In addition, the mechanism of action of the HTl structure in immobilizing copper species will be clarified and the influence of fluorinated layers on properties and performance of the catalysts will be systematically investigated. Then, the relationship among the precursor structure, the physicochemical properties of the catalysts and the catalytic performance will be clarified. Moreover, the project will gain the insights of the CO2 activation mechanism, the role of different basic sites and the reaction pathway over the developed catalysts. These results will provide theoretical understanding and the guidelines for the further design of highly effective Cu-based catalysts for methanol synthesis from CO2 hydrogenation.

CO2加氢转化为甲醇是CO2化学利用的重要途径，但存在CO2转化率和甲醇选择性较低的问题，且催化剂结构易在水汽存在条件下变得不稳定。我们前期研究发现CO2转化率主要取决于铜的分散度，而甲醇选择性则与强碱位比例有关。对于类水滑石衍生的铜基催化剂，层状晶粒分散性的提高可提升铜分散度，而氟离子的引入则有利于改善材料的表面碱性。本项目通过对类水滑石结构与形貌的调控得到层状晶粒高分散的前驱体，同时，将氟离子直接引入到层板结构中，然后，对氟化前驱体进行适当的热处理获得层状结构良好的氟修饰催化剂并测试其CO2加氢性能。另外，阐明类水滑石结构在稳定金属铜方面的作用机制，并系统研究层板氟化对催化剂性能的影响，从而建立前驱体结构、催化剂物化性质与反应性能之间的“构效关系”。本项目还将针对该体系催化剂深入探索CO2的活化机理、各碱位的功能以及具体的反应路径，为高效铜基催化剂的进一步开发提供理论依据和实际指导。

CO2加氢转化为甲醇是有望解决温室气体排放问题和缓解能源匮乏的有效途径，但存在CO2转化率和甲醇选择性较低的问题。本项目围绕催化剂反应性能的提升、构效关系和反应机理进行研究。获得的主要研究结果为：（1）通过四价金属离子和氟离子助剂的引入显著提升了以类水滑石为前驱体的Cu-ZnO-Al2O3催化剂的表面碱性，在保持较高CO2转化率的前提下，大幅提高了甲醇选择性，从而开发出了一种新型高效的二氧化碳加氢合成甲醇催化剂；（2）系统地研究助剂离子的种类、含量和引入方法对催化剂结构、各种物化性质与CO2转化率、甲醇选择性和长周期稳定性等反应性能的影响，建立前驱体结构、催化剂物化性质与反应性能之间完整的“构效关系”；（3）针对该体系催化剂深入探索反应过程中CO2的活化机理、各碱位的功能以及具体的反应路径，基于反应机理，进一步指导了新型催化剂的开发与应用。三年来，本项目共发表期刊论文15篇、会议论文4篇，包括Nature Chemistry、ACS Catalysis和Journal of Catalysis等一区论文11篇，另外，申请国家发明专利共10项，其中授权5项。鉴于本课题组在二氧化碳加氢领域内的贡献，应邀为Catalysis Science & Technology（2017, 7: 4580-4598）和Catalysis Toady（2018, DOI: 10.1016/j.cattod.2018.04.021）杂志撰写两篇二氧化碳加氢非均相合成高附加值烃类化合物和甲醇的指南性综述。另外，2016年6月中科院上海高等研究院完成了近1200小时连续运转的CO2加氢制甲醇的单管试验，目前，通过与中海油化的合作，正准备在海南东方市进行千吨级中试试验。本项目很好的支撑了催化剂的放大制备以及二代催化剂的研发。