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具有独特的电子和几何结构,原子精确控制的金纳米簇(<2 nm)成为一种新的具有广泛研究和应用前景的纳米催化剂.负载在氧化物表面的金纳米簇通常会在高于300°C时聚集或长大.人们已经通过多种方法成功制备了对于非原子精确控制的热稳定性的金纳米颗粒.主要包括利用金属与载体强相互作用,用可还原的金属氧化物来稳定金纳米颗粒;利用物理阻隔作用使用高比表面积的载体或制备核壳、纳米粒子镶嵌在载体中来稳定金纳米颗粒.对于原子精确控制的金纳米簇,由于其外边包覆着一层配体,将其负载到载体上时要保证配体不被破坏才能保证金纳米簇的结构完整性,负载后通常要除去配体才能使催化活性位曝露出来.目前,高热稳定性(>300°C)的金纳米簇的制备方法还较少.由于金与SiO_2相互作用较弱,将超小(<2 nm)的金纳米粒子包覆于其中非常困难.因此,本文首先制备了1.3 nm的含有硅酯键的巯基配体(3-巯丙基三甲氧基硅烷)保护的Au_(25)[SC_3H_6Si(OCH_3)_3]_(18),然后将其在刚成核的SiO_2表面与正硅酸四乙酯共水解,得到了既保留了Au_(25)的完整结构,又避免了Au_(25)之间相互水解的Au_(25)(SC_3H_6SiO_3)_(18)@SiO_2纳米材料.漫反射固体紫外-可见光谱证明了Au_(25)在包覆完成后结构的完整性.透射电镜结果表明,Au_(25)纳米簇焙烧至400°C未发生明显聚集长大.对硝基苯酚还原实验结果表明,不同温度处理后的Au_(25)@SiO_2配体在200°C开始脱除,温度高于传统的负载型Au_(25)催化剂,表明Au_(25)是在SiO_2内部而不是在表面,从而使配体不易离去.400°C处理后的Au_(25)@SiO_2对4-硝基苯酚还原表现出最高的反应活性,表明该纳米簇在400°C处理后没有发生明显聚集长大.
Gold nanoclusters (<2 nm) with unique electronic and geometrical structures and atom-precise control have become a new nanocatalyst with a wide range of applications and prospects.Gold-supported nanoclusters on oxide surfaces typically grow above 300 ° C. Gold nanoparticles that have been successfully prepared for non-atom-accurate control of thermal stability have been successfully prepared by a number of methods, mainly including the use of strong interaction of metals with the support, stabilization with reducible metal oxides Gold nanoparticles; the use of physical barrier to use a high specific surface area of the carrier or preparation of the core-shell nanoparticles embedded in the carrier to stabilize the gold nanoparticles.For the precise control of atomic gold clusters, because of its outside coated with a layer of ligand , When it is loaded on the carrier, the structure integrity of the gold nanocluster can be ensured without damage to the carrier, and the ligand is usually removed after being loaded to expose the catalytically active position .High thermal stability (> 300 ° C) Of the gold nanoclusters are less prepared.With the weak interaction between Au and SiO 2, it is very difficult to coat ultra-small (<2 nm) gold nanoparticles in it.Therefore, The Au_ (25) [SC_3H_6Si (OCH_3) _3] _ (18) protected by the silyl ester bond-containing thiol ligand (3-mercaptopropyltrimethoxysilane) (25) (SC_3H_6SiO_3) _ (18) @ SiO_2 nanocrystals with the mutual hydrolysis of Au_ (25) were obtained by co-hydrolyzing tetraethyl orthosilicate with tetraethoxysilane The structure of Au 25 was confirmed by UV-Vis spectroscopy.The results of TEM showed that there was no obvious aggregation and growth of Au 25 nanoclusters after calcination to 400 ° C. The experimental results of the phenol reduction show that the Au_ (25) @ SiO_2 ligands at different temperatures begin to be removed at 200 ° C, and the temperature is higher than that of the conventional supported Au_ (25) catalyst, indicating that Au_ (25) But not on the surface, so that the ligand is not easy to leave.The Au_ (25) @ SiO_2 treated at 400 ° C showed the highest reactivity to 4-nitrophenol reduction, indicating that the nanocluster did not Significant aggregation occurred.