【作者】 张超；

【导师】 周钰明；

【作者基本信息】 东南大学 ， 化学工程与技术， 2015， 硕士

【摘要】 负载型Pt基核壳催化剂在烷烃脱氢、CO氧化、氮氧化物还原等反应中具有较好的催化性能,在催化领域得到了广泛的应用,负载型Pt基核壳催化剂的催化性能主要取决于金属粒径的大小以及载体的种类,Pt纳米颗粒具有较高的表面能,高温条件下容易发生团聚现象,随着Pt颗粒粒径的增大催化剂的催化性能迅速降低。本论文从提高Pt纳米催化剂的热稳定性出发,利用Si02封装金属粒子的方法限制Pt粒子的团聚,提高了催化剂的热稳定性,采用XRD、BET、TEM、SEM和TGA等方法对催化剂进行表征,以对硝基苯酚的还原反应为探针考察了Ptencap/mSiO2 (HSC550)、mSiO2/Pt/MOx/Fe和Fe@Pt/Ti(OH)4的催化性能,并取得了一些结论,具体内容如下：1、通过NaBH4还原K2PtCl4制得Pt纳米颗粒,负载于水热法制得的碳球表面得到Pt/C,以CTAB为模板剂,TEOS为硅源在Pt/C表面封装mSiO2层制得mSiO2/Pt/C,焙烧除去mSiO2/Pt/C中的碳球制备了HSC550中空催化剂。350℃焙烧后Pt/C表面的Pt颗粒己发生团聚,mSiO2/Pt/C经550℃焙烧后其中的Pt粒子并未发生明显的团聚现象,说明mSiO2对Pt粒子具有较好的保护作用,能有效提高催化剂的热稳定性。随着焙烧温度的升高,mSiO2/Pt/C中的碳球不断除去,逐渐形成中空结构,HSC550催化对硝基苯酚还原反应的催化活性最好,说明中空结构可以提高HSC550的催化性能。HSC550重复使用5次之后催化对硝基苯酚还原反应的催化活性并未明显降低,该催化剂可以重复使用。2、分别以TBOT为前驱体制得纳米TiO2、CeO2,负载于a-Fe2O3表面得到MOx/a-Fe2O3(M为Ti或Ce),将Pt纳米颗粒负载于MOx/a-Fe2O3表面制得Pt/MOx/a-Fe2O3,在Pt/MOx/a-Fe2O3表面封装mSiO2层制备了mSiO2/Pt/MOx/a-Fe2O3,对其进行氢还原制得mSiO2/Pt/MOx/Fe核壳催化剂。在这个催化系统中,Pt颗粒被封装在mSiO2层中,提高了mSiO2/Pt/MOx/Fe的热稳定性。500℃焙烧的mSi02/Pt/Ce02/Fe催化对硝基苯酚还原反应的催化活性最好,随着焙烧温度升至700℃,mSiO2/Pt/CeO2/Fe中的纳米Ce02和Pt颗粒部分发生团聚,mSi02/Pt/Ce02/Fe催化对硝基苯酚还原反应的催化活性明显降低,说明mSi02/Pt/Ce02/Fe的抗焙烧性能较差。mSi02/Pt/Ti02/Fe经700℃焙烧后催化活性并未明显降低,说明mSiO2/Pt/TiO2/Fe具有较好的热稳定性。Ce02的功函数比TiO2低,电子富集区电子密度更大,500℃焙烧的mSiO2/Pt/CeO2/Fe催化活性最高。3、采用水热法在α-Fe2O3表面包裹碳层得到α-Fe2O3@C,将Pt颗粒负载于α-Fe2O3@C表面得到α-Fe2O3@C/Pt,通过TBOT和TEOS的水解在a-Fe2O3@C/Pt表面先后包裹Ti02和mSiO2,制得α-Fe2O3@C/Pt/TiO2/mSiO2,焙烧除去碳层得到α-Fe2O3＠Pt/TiO2/mSiO2,利用强碱腐蚀a-Fe203@Pt/Ti02/mSi02中的Ti02得到a-Fe2O3@Pt/Ti(OH)4,对其进行氢还原制得Fe@Pt/Ti(OH)4核壳催化剂。Fe核与Ti(OH)4纳米棒之间出现空腔,Fe@Pt/Ti(OH)4中的Pt颗粒分布在Ti(OH)4纳米棒之间,500℃焙烧后Pt颗粒不易团聚,提高了Fe@Pt/Ti(OH)4的热稳定性。当焙烧温度达到700℃时,Ti(OH)4纳米棒分解为二氧化钛得到Fe@Pt/TiO2,催化剂依然保持着核壳结构。Fe@Pt/TiO2中的TiO2与Pt颗粒之间有较强的相互作用,其在对硝基苯酚的还原反应中催化性能迅速提高,约为Fe@Pt/Ti(OH)4的1.5倍。更多还原

【Abstract】 The supported Pt yolk@shell nanocatalysts is invaluable in many important industrial processes such as propane dehydrogenation, CO oxidation and the reduction of NOx. The catalytic performance of Pt nanocatalysts is closely related to the size of Pt particles and the kinds of support materials. However, Pt NPs tend to aggregate to reduce surface energy. This seriously affects the application prospect of Pt nanocatalysts. In this paper, we used a "protection-calcination" strategy to improve the thermal stability of Pt nanocatalyst, and the prepared samples were characterized by X-ray diffraction (XRD), N2 adsorption-desorption isotherms (BET), transmission electron microscopy (TEM), scanning electron microscope (SEM), and thermosgravimetric analysis (TGA). Lastly, the reduction of p-nitrophenol was employed as a probe reaction to test the catalytic performance and we have got several results, the main results are as follows:1. A novel strategy has been developed to synthesize Ptencap/mSi02 hollow nanocatalyst (HSC550). This method involves the preparation of Pt/C, the formation of mSiO2, and finally the removal of nanocarbon spheres (NCSs) by calcinations. The catalytic evaluation was tested on the reduction of p-NPh to p-APh. It was found that Pt/C catalyst tend to sinter after calcinations at 350℃, however, mSiO2/Pt/C could resist sintering up to 550℃.It shows that mSiO2 could improve the thermostability of Pt catalyst. NCSs could be removed during the process of calcinations. When the calcination temperature is 550℃, the obtained materials exhibited the highest catalytic activity. The hollow sphere structure played a key role in the high catalytic performance. The synthesized Ptencap/mSiO2 hollow nanocatalyst showed an excellent recycl ability.2. The magnetic mSiO2/Pt/MOx/Fe nanocatalysts with a TiO2 or CeO2 layer have been fabricated successfully. The obtained nanocapsules were characterized by several techniques, including transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersion X-ray analysis (EDX). The catalytic evaluation was tested on the reduction of 4-NP to 4-AP monitored by UV-Vis spectroscopy. In this system, the mesoporous SiO2 shell served as an effective barrier to prevent the aggregation of Pt NPs. Besides, the oxide layers have an apparent co-catalysis effect to improve the catalytic activity. ThemSiO2/Pt/MOx/Fe samples exhibited entirely different catalytic activity and we propose a possible mechanism to explain the results. Finally, the synthesized mSiO2/Pt/MOx/Fe nanocatalysts showed an excellent recycl ability.3. A 3D hierarchical magnetic Fe@Pt/Ti(OH)4 nanoarchitecture has been synthesized successfully. TEM and SEM images were used to confirm the success of each of the synthesis steps. And the reduction of 4-NP to 4-AP was employed to evaluate their catalytic performance. The large surface area guaranteed the catalyst of a well catalytic performance. Furthermore, the as-prepared nanocapsule shows an excellent anti-sintering property for the physical barrier effects of Ti(OH)4 nanorods. Lastly, Ti(OH)4nanorods disappeared after calcination at 700℃ and the calcined sample showed the highest catalytic activity in our work due to the decomposition of Ti(OH)4.更多还原