单层二硫化钼/钨负载单原子非贵金属催化木质素基芳醚/酚加氢脱氧反应研究

Monolayer MoS2 or WS2 performs superior activity in many reactions due to unique electronic band structure and improved electric conductivity in comparison with their 3D bulk form. There are also a large number of surface defects that can act as anchors for metal atoms on monolayers. Moreover, a simple and well-defined structure would offer a setup in which to combine the theoretical research, model research and realistic application in catalysis. Based on above advantages, we will study monolayer MoS2 or WS2 supported Fe, Co and Ni single-atom catalysts (SACs) in catalysis. Following the strategy of oriented decoration of sulphur vacancies, we first prepare defects-abundant monolayer supports via chemical exfoliation and then screen out metal complexes with sulphur containing ligands. Hydrothermal method and atomic layer deposition will be used for the synthesis of SACs. Then we will test the SACs in hydrodeoxygention (HDO) of lignin-derived phenolic and ether compounds. During the tests, we will investigate the effects of metal type, loading amount and synergy of multi-components on the whole conversion, product selectivity and deactivation over SACs, before screening of several practical catalysts. After that, we will study the location and oxidation state of single-atom metal sites to confirm the interactions between metal and supports by using different characterizations such as EXAFS, HAADF-STEM and DFT calculation. We will focus on the formation energy of sulphur vacancies and the adsorption and activation of C-O bonds over single-atom sites. At last, real active sites and relationships between the structures of SACs and their catalytic activities will be deeply studied. This project would provide scientific foundations to the development of non-noble metal SACs supported by two-dimensional functional substrates and set up a new catalytic system of high-efficiency activation and conversion of C-O bonds in lignin-derived aromatic ethers and phenols.

基于单层二硫化钼/钨具有由独特的电子结构和增强的导电性带来的优越催化性、丰富的可锚定金属单原子的表面缺陷以及结构简明带来的构建理论-模型-实验之间桥梁的便利等优点，本项目拟从化学剥离制备单层二硫化钼/钨载体入手，基于缺陷定向沉积策略，筛选特定含S配体的金属配合物为前驱物，采用水热法和原子层沉积法制备Fe、Co、Ni非贵金属单原子催化剂；构建木质素基芳醚/酚化合物的加氢脱氧评价体系，考察金属类别、负载量、多元组分协同等因素对转化率、产物选择性和催化剂稳定性的影响，优选出实用型催化剂；利用EXAFS、STEM、DFT等分析手段，研究单原子的落位及其与载体之间的电子转移作用对催化剂表面S缺陷位的生成和反应物C-O键的吸附活化等影响，进而揭示构效关系，确定活性中心。本项目有望为发展二维功能性载体表面沉积金属单原子提供技术支撑以及建立高效的木质素基芳醚/酚的C-O键活化转化新催化体系。

钴钼硫催化剂在木质素基生物油的加氢脱氧（HDO）反应中具有较大的应用前景，但是在低温高活性、高稳定性催化剂的开发以及反应机理和活性位点本质等关键性科学问题上还有待进一步完善。传统催化剂的组分和微观结构较为复杂，给开展真实活性位点的研究带来了困难。因此，亟需发展原子界面精准调控的低维二硫化钼/钨基模型催化剂，用以开展表界面化学反应研究。本课题研究主要围绕二维二硫化钼/钨材料的制备、单原子钴/镍等金属助剂的沉积、CoMoS界面位点与HDO反应活性之间的构效关系等核心问题展开，并以此为指导来设计新型高活性、高稳定性的实用型催化剂。主要进展如下：1、本项目通过研究溶液超声剥离法、锂离子插层法以及水热合成法来制备二维二硫化钼/钨基底并调控表面缺陷，发现了S缺陷是催化酚类底物HDO反应的活性中心；2、基于缺陷定向沉积策略，以金属硫脲配合物为前驱物，采用水热法在二维材料基底上沉积了Co、Ni等非贵金属单原子催化剂，大幅提高了HDO反应活性，提高了芳烃的选择性；3、考察了金属类别、负载量、负载方法等因素对HDO性能的影响，优选出最佳的CoMo组合催化剂；4、利用前沿精细结构分析，研究了Co-S-Mo原子界面及其电子效应对直接脱氧路径（芳烃选择性）的影响，确定活性中心为Co-S-Mo原子界面；5、最后将构效关系反馈到新催化剂的设计中，分别采用Co-MOF作为模板来反向沉积MoS2或二次水热法，制备出高稳定性、高活性的CoMoS薄片催化剂，实现了反应温度降低的目标（250 oC）。本项目为发展二维材料的表面结构调控提供了方法，并建立了高效的生物油定向制芳烃的新催化体系。