原子精度的金属纳米簇催化剂及催化CO加氢制备低碳醇的研究

Conventional metal nanoparticles catalysts have several major issues, in particular, the inherent size polydispersity and structural heterogeneity. These major limitations preclude fundamental investigations on the precise structure-catalytic activity relationships. Therefore, it is of paramount importance to attain atomically precise metal nanoclusters and use such nanoclusters as well-defined catalysts. . Atomically monodisperse M(n) nanoclusters (n=number of metal atom in cluster) are ideally composed of an exact number of metal atoms, e.g., n ranging from a dozen to hundreds (equivalent diameter from subnanometer to about 3 nm). These nanoclusters are unique and vastly different from their larger counterparts?metal nanocrystals (typically 3-100 nm). Small M(n) nanoclusters (e.g., n < 100) behave like molecules and exhibit strong quantum confinement effects; relatively larger ones (100 < n <200) exhibit intermediate properties between molecular behavior and metallic properties. Overall, the non-metallic behavior of M(n) in both size regimes is particularly important for nanocatalysis. More importantly, on the basis of their atom packing structures and unique electronic properties, these M(n) nanoclusters will permit a precise correlation of particle structure with catalytic properties and also allow for identification of catalytically active sites on the metal particle. This has long been the number one important task in nanocatalysis. By solving their atomic structure of the nanoclusters, one will be able to precisely correlate the catalytic properties with the exact atomic structure of the nanoclusters and to learn what control the surface activation, surface active site structure and catalytic mechanism. By learning these fundamental principles, one will ultimately be able to design new types of highly active and selective nanocatalysts for a variety of catalytic processes, such as selective hydrogenation of carbon monoxide.. The major challenge of carbon monoxide hydrogenation is the efficient control of the reaction selectivity to alcohols, which is attributed to the unraveled nature of CO hydrogenation process. Herein, it is expected that the efficient control of selectivity to alcohols would be achieved by using such M(n) nanoclusters catalysts .Such nanoclusters will not only provide new opportunities for unraveling catalysis of CO hydrogenation, but also promote the exploration of controlling CO hydogenation processes for alcohols. M(n) nanocluster catalysts will ultimately bring metal nanocatalysis to an exciting new level. We anticipate that atomically precise metal nanoclusters will constitute a new generation of nanocatalysts and will offer tremendous opportunities in nanocatalysis.

原子精度的金属M(n)纳米簇（M代表金属，n是簇中原子的数目）克服了传统金属纳米颗粒尺寸多分散和结构多异化的缺陷，在原子尺度上原子数目和原子排列结构精确可控，其独特的几何结构和电子结构，可以有效调控催化反应历程，实现高选择性制备目标产物。本项目将通过实验手段获得原子精度的非贵金属M(n)纳米簇；使用替代位点的方法制备双金属纳米簇，形成原子精度的金属簇@金属簇新型结构；单金属M(n)纳米簇作为基本结构单元自组装成多级结构的 (M(n))x纳米晶。分别以原子精度的金属M(n)纳米簇、金属簇@金属簇以及(M(n))x纳米晶作为催化剂催化CO选择性加氢作为目标测试内容，研究结构和性能之间的构效关系，揭示催化本质，进而调控CO加氢催化反应的历程，高选择性获得低碳醇。在原子尺度上调控金属纳米催化剂的微观结构以及调控CO加氢催化反应历程兼备学术创新和技术创新。

作为富煤少油的中国, 利用高效洁净煤炭资源技术, 开发“绿色燃料”具有重要的战略意义和应用前景。合成气转化制气体液体燃料,油品添加剂以及大宗化学品是煤炭资源洁净利用的重要途径之一 ,但是有能力控制合成气转化的最终产物是有限的,因为合成气转化的产物较多且产物分布较广。在催化剂的作用下，CO 发生碳氧键断裂以形成醇中的烷基，再与未发生碳氧键断裂的CO 结合生成醇,其主要副产物为甲醇、CO2 和各种烷烃，如何通过设计制备高活性和高选择性的催化剂进一步提高醇类的选择性是目前该技术的研究关键。本项目深入细致地探索不同金属纳米催化剂的制备方法，利用独特的结构性质和电子性质，研究其对CO 加氢反应过程的影响，调控反应历程，使其对低碳醇的合成具有高活性和高选择的催化能力。本项目结合Co基双金属在合成气转化反应的特点，以Pd和Cu原子作为晶种，过Co在Pd或者Cu纳米晶表面异相成核，形成了内部球状核心，表面为一维枝状结构的钴基纳米团簇。通过调节Pd和Cu的含量，此CoPd或CoCu催化一氧化碳选择性加氢产物可以有目的性地往重质烃、轻烯烃以及含氧化物方向调控。Pd元素的适当添加，可以有效的提高一氧化碳的转化率以及增强链增长能力，有利于重质烃的生成。适当添加Cu可以形成更多的轻烯烃和含氧化合物。一维CoPd双金属纳米催化剂的 Anderson-Schulz-Flory分布的ɑ链增长因子可以达到0.9，而同等条件下CoPd纳米颗粒仅为0.64，显示了一维CoPd纳米催化剂良好的链增长能力。一维CoPd纳米催化剂更有利于形成高碳数链状烷烃，而颗粒状CoPd纳米催化剂更有利于形成中等碳数不饱和烯烃。因此通过定向调控CoPd纳米团簇的结构，可以高选择性得到不同的碳氢化合物。根据此双金属的合成机理,我们还研究了以Pt基双金属,制备了结构新颖的PtCo@Co核壳立方体,PtCo八立方体,PtCo凹面立方体等,并在C=C和C=O键的加氢中表现了特异的能力.以及研究一维结构的稀土氧化物催化甲烷氧化偶联制烯烃.以上结果共发表有本项目资助号的SCI论文18篇，申请8项发明专利。并由此结果获得到荷兰壳牌公司资助的15万美元以及英国能源技术研究所的25万英镑的项目的资助.项目负责人获得上海市浦江人才计划的资助.