多级孔二氧化硅纳米薄片限域的金/过渡金属氧化物催化剂的构筑及催化选择性加氢性能研究

Selective hydrogenation of α,β-unsaturated aldehydes or ketones is an important reaction for both fundamental research and applied research. In general,small size gold nanoparticles exhibit high catalytic activity. However, they are typically unstable and tend to sinter into larger particles or detach from the support, which always leads to the decrease of activity and even deactivation. Using graphene oxide with a large surface as support,transition metal oxide nanoparticles（such as TiO2、Fe3O4 and CeO2）are uniformly dispersed on the surface of graphene oxide, and then the intimate nanocontact of gold and transiton metal oxide is prepared through controlling the deposition position of gold nanoparticles.The above nanocomposites are encapsulated with thin silica layers through the hydrolysis of tetraethylorthosilicate. Finally hierarchically porous silica nanosheet-confined gold and transition metal oxide catalysts are constructed by the removal of the organic template agent and graphene. By investigating the relationship between preparation parameters and the structure of gold catalysts,the law of the preparation process is explored. The relationship beween the activity of oxygen species and catalytic activity of gold catalysts in H2-D2 exchange reaction and simple hydrogenation of alkyne and alkene is studied, so the active sites for hydrogenation dissociation are identified. The catalytic performances and stability of gold catalysts are investigated for gas phase and liquid phase selective hydrogenation of α,β-unsaturated aldehydes or ketones. Combined with the characterizations results of gold catalysts, the relationship between structure and property of gold catalysts is clarified.Our research will not only provide theoretical foundations for the designing of gold nanocatalysts,but also obtain kinds of high stability and activity gold nanocatalysts with potential industrial application prospect.

金纳米催化α,β-不饱和醛(酮)选择性加氢具有重要的基础研究和应用研究价值。通常，小尺寸的金纳米粒子具有高催化活性,但其易团聚或从载体上流失导致活性下降甚至失活。本项目以大比表面积的氧化石墨烯为载体，在其表面均匀分散过渡金属氧化物纳米粒子（TiO2、Fe3O4和CeO2等），调控金溶胶的沉积位置，使金选择性地与过渡金属氧化物接触，在所得材料的表面原位包覆二氧化硅薄壳，最终构筑大比表面多级孔二氧化硅纳米薄片限域的金/过渡金属氧化物催化剂。通过研究制备参数与催化剂的结构之间的关系，探索制备过程的规律。通过关联界面氧物种活性和催化剂在H2-D2交换反应和简单炔烃、烯烃反应中的活性，确认氢气解离活性中心归属。通过研究催化剂在α,β-不饱和醛（酮）选择性加氢反应中的催化性能和稳定性，阐明其结构与性能的关系。本研究不仅为金催化剂的设计提供科学理论依据，并有望获得一类具有工业应用前景的高性能金纳米催化剂

在化学反应或催化剂再生过程中，小尺寸的金纳米颗粒极易迁移和团聚，导致其活性下降乃至失活，在保持高活性的同时提高稳定性是金纳米催化剂的基础研究和工业应用必须解决的关键问题。本课题制备了原子数精准的巯基保护的金纳米团簇Aun(SR)m并担载于金属氧化物上获得了一种高稳定性和独特选择性的催化剂。在4-硝基苯甲醛转移选择加氢反应中，Au38(SR)24/CeO2具有最高的活性，尤其显示出专一的醛基加氢选择性和良好的稳定性。其活性和稳定性与Au38(SR)24的独特电子结构有关，优异的选择性源于醛基而非硝基在Au38(SR)24上的优先吸附。该工作初步揭示了配体影响金纳米团簇催化选择加氢性能的机制，为调控金纳米催化剂的选择性提供了参考。SBA-15担载的Au纳米催化剂在喹啉选择加氢反应中呈现有较好的活性、优异的选择性和极佳的稳定性。其活性源于金纳米颗粒的适宜尺寸和SBA-15良好的传质效果，优异的选择性与含氮杂环在Au表面的选择性吸附有关，极佳的稳定性与SBA-15的孔道对Au的限域有关。在上述体系中引入少量的Pt，可显著提升Au@SBA-15催化剂的活性，同时保持原有的高选择性和稳定性。在极为温和条件下，喹啉的转化率和1,2,3,4-四氢喹啉的选择性分别达到95%和99%。该催化剂的本征加氢活性高于已报道的绝大多数贵金属纳米催化剂。Au和Pt的协同效应导致Pt呈富电子状态，抑制了喹啉类化合物在Pt表面的强吸附，促进了H2的吸附和解离，提高了催化活性。适量FeOx的引入能够调节Au和FeOx的界面长度，增加活性位点的数量，提升Au-FeOx@SBA-15的催化性能。C=O在FeOx上的选择性吸附还显著提升了所得催化剂的选择性。水滑石衍生的镍铝复合氧化物对金纳米颗粒的限域作用赋予该催化剂优异的选择加氢活性和稳定性。底物中不同还原基团在载体上的选择性吸附还可实现4-硝基苯乙烯中硝基和乙烯基的加氢的可控切换。总之，本课题从金纳米团簇的结构设计、载体对金纳米颗粒的分散和限域以及其对底物的选择性吸附调节、Au和Pt的协同作用等入手制备了一系列高稳定性、高活性和高选择性的金纳米催化剂，为构筑高性能的金纳米催化剂提供了借鉴。