Fabrication And Properties Investigation Of Ordered Mesoporous Materials Supported Noble Metal Nanocatalysts

Noble metal nanoparticles（NPs） have been widely used in heterogeneous catalysis because of their unique physical and chemical properties. Unfortunately, high price and scarcity limit their large-scale application in industry. In order to improve their catalytic activity and utilization efficiency, it is needed to reduce the size of the noble metal NPs as much as possible. However, due to the high surface energy, noble metal NPs have high tendency to aggregate, which will decrease their surface area and result in a remarkable reduction in their performance. Recent developments in ordered mesoporous materials have opened new possibilities to get small sized noble metal NPs with uniform dispersion. Up to now, numerous methods have been developed to generate nanoparticles hosted in the channels of such materials. However, their practical application is still hindered by some drawbacks:（1） Most of these synthetic procedures are complex and perhaps involve toxic stabilizer agents or hazardous reducing agents which may be associated with environmental toxicity;（2） These ordered mesoporous materials usually suffer from seriously decrease of surface areas or block of pore channels after loading the metal NPs, resulting in low mass-transport efficiency in the reaction. Thus, this thesis is aiming to find a facile and green method for preparing ordered mesoporous materials supported noble metal NPs composite materials, and investigating their catalytic properties. The main results are listed as below:（1）By using a simple in-situ auto-reduction strategy, we have successfully fabricated the Ag@FDU-15 nanocomposite in which the Ag nanoparticles are monodispersed in the channels of ordered mesopolymer FDU-15. The silver nanoparticles are uniformly dispersed with a mean diameter of 5.6 ± 0.5 nm. The effects of experiment parameters on the obtained products and the formation mechanism of Ag@FDU-15 were investigated. When used as hydrogenation catalyst, the Ag@FDU-15 nanocomposite exhibits excellent catalytic performance and reusability for the reduction of 4-nitrophenol（4-NP） in the presence of Na BH4. Moreover, the Ag@FDU-15 nanocomposite shows high thermal stability even at 500 o C.（2） By using trisodium citrate as chelating agent to control the release rate of Au3+, highly dispersed Au NPs have been successfully assembled in the channels of FDU-15. The catalytic test demonstrates that the as-prepared Au@FDU-15 nanocomposite has excellent catalytic performance and reusability for the reduction of 4-nitrophenol（4-NP） in the presence of Na BH4. Moreover, we have successfully achieved the Pd@FDU-15 and Pt@FDU-15 nanocomposites by using the similar method, indicating the versatility of this method.（3） By using hybrid mesoporous phenolic resin-silica（OMPS） nanocomposite as parent material, the ordered mesoporous silica supported Pt NPs nanocompostie（Pt@OMS） has been obtained. The size of the supported Pt NPs is about 2 nm. Phenolic resin polymer here is supposed to be the key role in preventing the aggregation of Pt NPs during their formation process and making contributions both to enhancing the surface area and enlarging the pore size of the support. The Pt@OMS proves to be a highly active and stable catalyst for both gas-phase oxidation of CO and liquid-phase hydrogenation of 4-nitrophenol.（4） By using the wetness impregnation method, the CeO₂ NPs have been assembled in the channels of the previous prepared Pt@OMPS materials. After calcination, we have successfully obtained the CeO₂ modified ordered mesoporous silica supported Pt NPs nanocompostie（Pt-Ce@OMS）.The structure of Pt-Ce@OMS was characterized by small angle X-ray scattering, wide angle X-ray diffraction, nitrogen sorption, transmission electron microscopy（TEM） and scanning transmission electron microscopy（STEM）.The characterization results indicate that channels of Pt-Ce@OMS still open after the CeO₂ NPs impregnation. Compared with the Pt@OMS, the Pt-Ce@OMS nanocomposite exhibits higher thermal stability. The size and dispersion of the supported Pt NPs are still maintained even after calcination for 5 h at 773 K in air.