负载型金催化剂上芳香硝基化合物选择加氢制相应芳胺：金的尺寸效应

The chemoselective hydrogenation of nitroarenes to the corresponding anilines is one of the important reactions in the synthesis of fine chemicals. When other unsaturated functional groups (e.g., -C=C, -C≡N, etc.) existed in the same molecule as the nitro group, it is quite challenging to chemoselectively hydrogenated the –NO2 while keeping other functional groups intact. It has been reported that the gold catalysts showed unique chemoselectivity for this kind of reactions. Take the selective hydrogenation of the 3-nitrostyrene as an example, recently, we for the first time developed a gold catalyst only active for the hydrogenation of the nitro group while inert for the –C=C by using the thiolated Au25 and the ZnAl-hydrotalcite as the precursor of the catalyst. Inspired by the previous result, we’d like to further pursue the intrinsic origin of the activity and selectivity for this kind of reaction over gold catalysts by constructing the metal-support interface via tuning the size of gold and the nature of the supports. The gold clusters with different number of gold atoms are examples of the state-of-the-art scientific research. We will take them as the precursor for gold to tune the size of supported gold catalysts. The stabilization of gold with different sizes over different support will be studied by combing the experiment and theoretical calculations. The as-prepared gold catalysts will be applied to the chemoselective hydrogenation of the functionalized nitroarenes. The catalytic behavior will be analyzed correlated to the size of gold and the nature of the supports, so that the key factors affecting the adsorption and activation of the substrates and/or hydrogen can be summarized. Based on the above results, the catalytic mechanism for this kind of reaction over gold will be proposed. We believe this project will be benefit to realize the control of gold from the atomic level. Furthermore, it will provide profound fundamental acknowledge for catalytic mechanism of the chemoselective hydrogenation over gold catalysts, which will guide the design of new gold catalysts with high activity and selectivity.

芳香硝基化合物选择加氢制相应的芳胺是精细化工领域的重要反应之一。当底物分子中同时含有其它不饱和基团（如-C=C、-C≡N等）时，只选择加氢硝基而保留其它功能团颇具挑战性。金催化剂对该类反应表现出很高的选择性，以3-硝基苯乙烯为例，项目申请人前期成功开发出只对硝基有加氢活性而对-C=C惰性的金催化剂。基于此，本项目将通过调控金的尺寸和载体的性质，构筑金-载体界面，深入研究其影响该类反应的活性和选择性的本质原因。采用具有不同原子数的金团簇为前驱体，以实验和理论相结合的方法，研究金在不同载体上的稳定机制。研究金的粒径效应对负载型金催化剂在芳香硝基化合物选择加氢反应中的催化行为的影响，考察影响反应物的吸附和活化的关键因素，阐明金催化该类反应的机理。本项目的实施，有望从原子水平上实现金催化剂的可控合成，有利于系统地认识金催化选择加氢反应的机理，为设计兼具高活性和高选择性的金催化剂提供理论指导。

以锌铝水滑石负载的Au25纳米团簇为催化剂前驱体，所得Au催化剂在3-硝基苯乙烯选择加氢反应中对3-氨基苯乙烯表现出很高的选择性，但对影响硝基选择加氢的活性和选择性的本质尚缺乏系统和深刻的认识。本项目通过在纳米、亚纳米尺度控制Au的粒径，选择水滑石（锌铝、镁铝、镍铝等）、Al2O3、SiO2等作为载体，制备了一系列负载型Au催化剂，并通过球差校正电子显微技术、X-射线吸收光谱、衰减全反射傅里叶变换红外光谱、原位傅里叶变换红外光谱、X射线光电子能谱、核磁共振谱等表征手段对这一系列催化剂的Au颗粒的尺寸分布、配位环境、反应机理等进行表征。系统研究了载体的种类、Au的粒径尺寸等对Au催化剂反应性能的影响，并将该类催化剂拓展应用于不饱和醛制不饱和醇的反应中。本项目的研究结果，有助于深入理解负载型Au催化剂上选择加氢反应的选择性和活性的本质原因。此外，本项目支持的光热协同催化课题亦取得了实质性进展，解决了Pt催化剂在丙烷燃烧过程中氧中毒的问题，大幅降低了该反应的起活温度。