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Fabrication and Characterization of Pt Nano-cluster /photosensitive Polyimide Hybrid Membrane and Its Research for Benzene Hydrogenation

Author: LongShuai
Tutor: ZhangAiQing
School: Central South University for Nationalities
Course: Organic Chemistry
Keywords: platinum nano-clusters polyimide benzene hydrogenation cyclohexene membrane reactor
CLC: O643.32
Type: Master's thesis
Year: 2009
Downloads: 33
Quote: 1
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Abstract


Partial hydrogenation of benzene to cyclohexene is a typical organic catalytic reaction and a subject of great interest, from both theoretical and practical aspects. In spite of the fact that cyclohexene is an intermediate product of the benzene hydrogenation, cyclohexane is the end product rather than cyclohexene, owing to the kinetically favouring hydrogenation of cyclohexene to cyclohexane (standard heats of formation of cyclohexane and cyclohexene are -153.4kJ/mol and -63.9kJ/mol respective). At present, ruthenium-based catalysts are the vast majority of catalysts on the benzene hydrogenation to cyclohexene. It is more difficult to obtain cyclohexene as the platinum has a higher hydrogenation activity than ruthenium. So, there are little researchs about it. The platinum-based catalysts have such characteristics as high catalytic activity and long life. And the ruthenium-based catalysts have so many shortcomings like inadequate supply, complexity of preparing, inefficient circular using and so on. Therefore, it is necessary to explore the catalytic activity of the platinum catalyst in the partial hydrogenation of benzene further.In this work, we fabricated Pt nano-cluster /photosensitive polyimide swollen membrane reactor (Pt/PSPI) consisting of inorganic material of monodisperse platinum group nano-clusters and organic material of photosensitive polyimide (PSPI) with the method of embedment. The structure and performance of hybrid membrane were characterized and analyzed. The membrane reactor was used to obtain the high selectivity of cyclohexene in catalytic hydrogenation reaction of benzene.There are three parts to be included in this paper: 1. The stabile platinum metal clusters were obtained with stabilizer Polyvinylpyrrolidone (PVP, K30) and reducing agent glycol by microwave irradiation (MW), which average diameter of particles was 3.7 nm. X-ray diffraction analysis showed the good crystalline form and stability of the platinum metal cluster. The characteristic of MW are short irradiation time and uniform heating. And MW can be applied to prepare a variety of nano-metal cluster.2. It was mixed with 1, 5-bisaminophenyl-1, 4-pentadien-3-one ,3,3’,4,4’-benzophenonetetracarboxylic dianhydride and 4,4’-Diaminodiphenyl ether to synthesize PSPI by traditional two-step method. Polyimide acid (PAA,which solid content was 12%) was prepared in first step, and then the catalysts which dispersed in N-methyl-2-pyrrolidone (NMP) were added to PAA by stirring. Lastly, Pt/PSPI hybrid membranes were obtained by heating 1h in 80℃、150℃、200℃、250℃、300℃respectively for further imiding with the method of temperature programmed. The Pt content of hybrid membrane was 5.5 wt.%. Platinum nano-particles were dispersed uniformly in membrane of PSPI by embedding, thanks to the nano-particles could be dissolved in NMP and the NMP was solvent for synthesis of PSPI. X-ray diffraction analysis showed that Pt nano- particles were stably loaded on polyimide film with good crystal form in pre and post reaction. X-ray photoelectron spectroscopy analysis showed that complex phenomena occurred between platinum atoms and nitrogen or oxygen atoms, which was force between atoms. Thereby it would to reduce the question of losing the catalytic active center.3. The products of benzene hydrogenation were cyclohexene and cyclohexane when the catalyst was Pt/PSPI hybrid membrane. It can be seen that the conversion of benzene and the yield of cyclohexene getting the peak after 10h increased with the time. The highest selectivity of cyclohexene increased at first and then decreased, which exceeded 72% at 2h. There was no cyclohexene in products when the catalyst was only Pt nano-particles without PSPI, and the only product was cyclohexane. The formation of cyclohexene is influenced deeply by hybrid membrane, because the cyclohexene of production only could be found when the catalysts were Pt/PSPI rather than Pt. The experiment results of swollen show that cyclohexene is hard to swollen in hybrid membrane rather than cyclohexane. Accordingly, we can conjecture that the cyclohexene is separated from active center of catalytic hydrogenation and effused from the hybrid membrane so that they cannot be further hydrogenated to cyclohexane, once they appeared in reaction. So the selectivity of cyclohexene is higher than that of cyclohexane.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalytic reaction
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