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Study on the Active Sites of Supported Vanadium-Based Catalysts in Propane Oxidative Dehydrogenation

Author: YuXiaoChuan
Tutor: XiongGuang
School: Dalian University of Technology
Course: Industrial Catalysis
Keywords: Oxidative dehydrogenation situ Raman spectroscopy Supported Catalysts TPR XRD
CLC: O643.36
Type: Master's thesis
Year: 2009
Downloads: 137
Quote: 1
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Abstract


Oxidative dehydrogenation of light alkanes to olefins is an important way of using natural gas. Metal oxide catalysts show a good catalytic property in the reaction, especially vanadium-based catalyst. Different species can be formed on the supported vanadium catalyst, such as isolated, polymeric or crystalline structure. Introducing the second metal can help to form new surface species, which may play different roles in the reaction.Raman spectroscopy is an important tool to characterize the structure of metal oxide catalysts. Visible laser is used as excitation source in the conventional Raman spectroscopy. UV Raman spectroscopy is a new progress in the spectrum characterization. Previous studies suggest that some innovational results were obtained from UV Raman due to fluorescence free and resonance effect.In this paper Visible and UV Raman spectrometer, combined with other means of characterization, were used to inspect the structure of sole and binary vanadium-based catalysts, which are controlled by the preparation methods. When the loading is 0.5-15 wt % two-dimensional polymerized vanadium species are formed on the V2O5/γ-Al2O3 catalyst, and the crystalline V2O5 appears when the loading reaches 20 wt %. Two-dimensional polymerized vanadium species are propitious to the selectivity of alkane ODH. The molybdenum and vanadium species on the V2O5-MoO3 catalyst form a polymeric species in the sub monolayer region. When the loading reaches 30%wt, crystalline Al2(MoO43, AIVMoO7,AIV3O9, MoO3 and V2O5 appear on the surface, depending on different vanadium molybdenum ratio. Through the study of situ raman and TPR, it was found that crystalline speciecs are propitious to the selectivity of alkane ODH. The AIVMoO7 is easier to be reduced than Al2(MoO43.V-O-Mo bond is easier to lose lattice oxygen and harder to be replenished than Mo=O bond. Adding Mg changes the surface structure of the catalyst. Mg2V2O7 is formed with increasing the Mg amount. The appearance of Mg2V2O7 changes the redox properties of the catalyst, thus affacting the catalytic properties for ODH reaction.

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