有序介孔碳限域Au纳米催化剂活性中心的研究

Gold nanoparticles supported on metal oxides have shown interesting catalytic properties in the selective hydrogenation of nitroaromatics and selective oxidation of alcohols. To take advantage of the particle size effect while minimizing the interface interaction effect for gold nanoparticles with oxide, a less-interacting support such as activated carbon is required. But the investigation on active center and reaction mechanism of porous carbon supported gold nanocatalysts are limited. The major reason is the difficulty in synthesis of porous carbon supported gold nanocatalysts with well-controlled size. Herein this proposal will focus on the research on active centers for confined gold nanocatalysts of ordered mesoporous carbon in selective hydrogenation of nitroaromatics, as well as selective oxidation of alcohols and reaction mechanisms. Size-controlled ordered mesoporous carbon confined Au nanocatalysts are synthesized via the coordination-assisted solvent evaporation induced self-assembly. On the combination of the investigation on the particle size, electron chemistry and coordination of Au nanoparticles with the DFT calculations for the activation of H2 and O2 over C-modified gold surface, the active centers and reaction mechanisms would be proposed. Bimetallic particles such as AuPd can modify lattice distance, electron chemistry, and coordination, surface/subsurface carbon doping, and therefore provide active centers and reaction mechanisms different with single metals. This proposal will focus on the active centers for bimetallic catalyst and dehydrogenation of benzyl alcohols mechanism. Hybrid carbons containing size-controlled transition metal oxides such as TiO2, NiO and MnO, and rare-earth metal oxides such as CeO2 will be further applied to confine gold nanocatalysts to modify electron chemistry, and coordination for gold atoms, as well as the interfacial interaction between them. The investigation on the surface adsorption of H2, O2 and organic substrates will benefit for the illustration on active centers and reaction mechanisms, aiming for the enhancement of activity and selectivity in selective hydrogenation of nitroaromatics and selective oxidation of alcohols. The research may provide solutions for synthesis of aggregation, leaching-resistance Au nanoparticles, modification of electron chemistry for porous carbon supported gold catalysts, enhancement of activity and selectivity for nitroaromaics hydrogenation using H2 as a reducing agent and alcohols oxidation using O2 as an oxidizing agent, as well as provide new insights on active center for gold catalysts.

负载金催化剂被认为是用于芳香硝基化合物加氢、醇选择氧化反应的第二代催化剂。但碳载Au催化剂相关催化活性中心和作用机理的研究相对缺乏，针对芳香硝基化合物加氢反应的研究较少。本项目将在获得具有规整介孔结构的碳限域Au纳米催化剂基础上，调控Au纳米颗粒尺寸和配位结构，揭示催化活性中心和表面反应机理。利用双金属AuPd，调控原子间距、双金属电子化学、配位结构、表面/次表面碳掺杂等，阐释有序介孔碳限域AuPd双金属催化活性中心和醇脱氢反应机理。使用含金属氧化物纳米颗粒有序介孔碳为载体，限域Au纳米催化剂，调控Au电子性质、配位结构及氧化物-Au界面，调变有机物吸附构型，阐明反应机理，阐释活性增强和选择性(如硝基苯选择加氢为苯胺或偶氮苯等)调控机制。为以H2为氢源的芳香硝基化合物选择加氢和O2为氧化剂的醇选择氧化反应，提供具有高稳定性、活性和选择性的Au纳米催化剂，同时为Au活性中心研究提供新的思路。

金曾被认为是最不活泼的金属之一。这可能是由于在化学吸附过程中，Au的d带与吸附质分子轨道重叠较小。另一方面，杂环芳香化合物在催化剂表面的强吸附易导致其中毒失活。为此，本项目： 1）发现了金属d电荷密度对芳香化合物吸附活化和反应活性的调变规律，为设计高性能催化剂提供了新思路；2）提出了合金化与形成间隙固溶体策略，建立了稳定、电子结构可控的介孔碳限域金属纳米催化剂制备新路线；阐释了双金属、介孔碳载体中金属氧化物纳米颗粒与金界面作用调控Au电子性质机制，揭示了Au的d电荷密度调控规律；阐明了芳香硝基化合物还原和苄醇选择氧化反应的活性中心和反应机理；解决了多孔碳载体上Au纳米颗粒易聚集和流失、电子化学调控难等问题；3）利用d电荷密度描述符等，创制了高效、稳定的金属基纳米催化剂，变革了传统反应路径，实现了芳香化合物高效定向转化。