Pt Nanoparticles Supported On Highly-dispersed Titania Coated Inside Mesoporous Materials For Efficient Catalytic Hydrogenation

TiO2is an active catalytic supporter. Related research shows that its photocatalytic efficiency and supporter performance are closely related to phase composition. However, as a carrier, TiO2has obvious disadvantages, such as a low specific surface area, easy to be lost, difficult to be separated and recovered. For those reasons many researchers have been focused on possible materials supporting titania catalysts. Ordered mesostructured materials, which with adjustable pore size and close to maximal possible specific surface area provide wide opportunities for synthesis of advanced materials with different functionalities. For example, the use of a structured silica support would offer more space effect factors for the formation of the transition state of reaction system or induce controlled oxide nanoparticles growth. In addition, people keep a watchful eye on green chemistry and green chemical, and theirs awareness of environmental protection get stronger, so water as a green and environmental friendly reaction mediator, which gradually attract people’s eyes. Much more chemical reaction processes are expected to going in water, therefore, it is very necessary to improve hydrothermal stability and reusability of titania materials.The work presents sol-gel method to prepare titania composite materials support-ed Pt nanoparticles catalyst by using SBA-15(with p6mm symmetry) or KIT-6(with Ia3d symmetry) as substrate. The resulted materials prove to be remarkable supports for Pt nanoparticles for the catalytic hydrogenation of aromatic aldehydes, ketones, olefins and aromatic nitrocompounds. For comparison, we applied the homemade Pt/TiO2catalyst in these reactants. The main results are summarized as follows:In the first part, a series of composites of titania coated inside the mesoporous channels of SBA-15, TiO2@SBA-15(denoted as xTS) with different titania loadings, were prepared and characterized by XRD, N2-sorption, UV-vis. The characterization of the resulted composites confirmed that TiO2was highly dispersed inside the mesoporous channels of SBA-15host, even if the titania loading reached30wt.%when calcined two hours under623K. While calcined two hours under673K or773K, TiO2was still highly dispersed when the titania loading reached15wt.%. The introduction of titania into the mesopores of SBA-15makes TiO2@SBA-15possess amphiphilicity, so Pt particle size dispersed on supports can be modulated by changing titania loading and solvent of the H2PtCl6solution. The Pt nanoparticles for Pt/15TS-E-773catalyst, prepared by impregnation of the support in the ethanol solution of H2PtCl6, were uniformly dispersed on the xTS surface and the average Pt particle size was around7nm.In the second part, to investigate the catalytic performance of Pt/xTS catalysts prepared by different methods, we have carried out the catalytic hydrogenation of benzaldehyde. The Pt/15TS-E-773catalyst showed highest conversion (100%) and selectivity (>99%) for benzaldehyde hydrogenation with the TOF reaching6390h-1, even showed superior performance to Pt/TiO2catalyst with the TOF reaching1673h-1The benzaldehyde hydrogenation on the Pt/15TS-E-773catalyst in water went faster than in ethanol, and the catalyst can be reused for more than ten times in water. Pt/15TS-E-773catalyst can also catalyze the hydrogenation of a series of benzaldehydes with different substituents. Except for catalyzing the above-mentioned substrates hydrogenation, Pt/15TS-E-773catalyst can also catalyze hydrogenation of olefins, ketones and aromatic nitrocompounds. In all the investigated cases, the catalyst showed a very high activity. The TOF of hydrogenation nitrobenzene reached10102h-1in water, which was higher than previously reported.In the third part of this thesis, we also prepared another series of titania composites coated inside the mesoporous channels of KIT-6(TiO2@KIT-6, denoted as xTK), and Pt catalysts supported on xTK. All or most of TiO2of the samples5TK,10TK and15TK, was dispersed within the mesopores of KIT-6with amorphous state. The introduction and dispersion of TiO2on the KIT-6surface may enhance metal-support interactions of Pt/5TK, Pt/IOTK catalysts. As a result, the higher activity induced by Pt/10TK catalyst was achieved compared with Pt/KIT-6catalyst in the hydrogenation of benzaldehyde and nitrobenzene.