Preparation And Characterization Study Of Yolk@Shell Pt Nanocatalyst

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.