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  Synthesis, Characterization and Catalysis of Nanostructured Vanadia Model Catalysts for Partial Oxidation of Propane

Herbert, R. (2009). Synthesis, Characterization and Catalysis of Nanostructured Vanadia Model Catalysts for Partial Oxidation of Propane. PhD Thesis, Technische Universität, Berlin.

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Other : Synthese, Charakterisierung und Katalyse nanostrukturierter Vanadiumoxidmodellkatalysatoren für die partielle Oxidation von Propan

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 Creators:
Herbert, Rita1, Author              
Lerch, Martin, Referee
Schlögl, Robert1, Referee              
Schomäcker, Reinhard, Referee
Affiliations:
1Inorganic Chemistry, Fritz Haber Institute, Max Planck Society, ou_24023              

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Free keywords: vanadium; propane; catalysis; SBA-15; titanium Vanadia in selective oxidation
 Abstract: Nanostructured vanadia model catalysts supported by silica were synthesized in a multi-step procedure as well as through incipient wetness impregnation. Afterwards, the samples were characterized and tested in the oxidative dehydrogenation (ODH)of propane. Silica supports used were mesoporous SBA-15 and Aerosil 300. The multi-step synthesis includes a surface functionalization and an ion exchange with decavanadate ions. One aim of this study was the investigation of the in uence between two support materials and between different synthesis methods concerning the vanadia structure and to find a correlation to their catalytic behavior. Therefore, highly dispersed vanadia species with a similar vanadium density of 0.7 V atoms/nm2 were prepared. The samples were thoroughly characterized by nitrogen adsorption-desorption, small-angle XRD, TEM, XPS, Raman- and UV-vis spectroscopy. Furthermore, reactivity was tested with TPR besides catalytic test. It could be shown that the multi-step procedure has a stabilizing effect on the mesoporous material. After mechanical, thermal and hydrothermal treatment, the sample treated with surface functionalization shows a higher stability than blank SBA-15. The blank SBA-15 shows a signiffcant decrease of the BET surface area already at a mechanical treatment already at 75 MPa, whereas a signi cant change of the surface area in the multi-step samples appears not until at 376 MPa. After pressure treatment at 752 MPa no mesoporous structure can be observed anymore for blank SBA-15, but for the multi-step sample it is in parts still observable. The impregnated samples show the same behavior as blank SBA-15. The enhanced stability has a positive influence on reaction behavior. The multi-step sample pressed at 752 MPa shows in the ODH of propane a higher selectivity towards propene than the impregnated sample treated in the same way. This can be explained by accessibility of active sites within the samples. In the impregnated sample are more active sites blocked than in the multi-step sample, due to the complete loss of mesoporous structure. When comparing both support materials and the different synthesis methods, an increase of the degree of polymerization can be observed in the following order: VxOy/SBA-15 multi-step - VxOy/SBA-15 impregnated - VxOy/A300 multi-step - VxOy/A300 impregnated. It can be said that the spectroscopic data show a more distinct influence on the degree of polymerization of the support materials, whereas TPR data show clear differences among the synthesis methods. In the oxidative dehydrogenation of propane, no differences could be observed concerning the selectivities at similar conversions. This leads to the assumption that the reactivity is highly influenced by the composition of the gas phase. Another issue in this study were first investigations on an SBA-15/titanium system, which can be applied as a support material for vanadia. For this purpose, several loadings of titania were impregnated on SBA-15 and characterized. Additionally, a Ti/SBA-15 sample with vanadium was synthesized, spectroscopically characterized and tested in the oxidative dehydrogenation of propane. The results show for conversion and selectivity a similar behavior at a reaction temperature of 450 °C as vanadium on blank SBA-15, but clear differences at a reaction temperature of 500 °C. For V-Ti/SBA-15 at a reaction temperature of 500 °C a signiffcant increase of conversion of propane can be observed.

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Language(s): eng - English
 Dates: 2009-02-09
 Publication Status: Accepted / In Press
 Pages: 135 p.
 Publishing info: Berlin : Technische Universität
 Table of Contents: 1 Introduction and aim of study 1
1.1 Vanadia in partial oxidation reactions . . . . . . . . . . . . . . . . . . . . 2
1.2 Nanostructured materials as model catalysts . . . . . . . . . . . . . . . . 4
1.2.1 Surface structure of amorphous silica . . . . . . . . . . . . . . . . 5
1.2.2 Structure of supported vanadia . . . . . . . . . . . . . . . . . . . . 7
1.3 Selective oxidation of propane . . . . . . . . . . . . . . . . . . . . . . . . . 11
2 Experimental set-ups and basic principles 13
2.1 Nitrogen adsorption-desorption . . . . . . . . . . . . . . . . . . . . . . . . 13
2.1.1 BET surface area . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.1.2 Pore size analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.2 X-ray di raction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.3 X-ray photoelectron spectroscopy . . . . . . . . . . . . . . . . . . . . . . . 22
2.4 Electron microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.4.1 Transmission electron microscopy . . . . . . . . . . . . . . . . . . . 27
2.4.2 Scanning electron microscopy . . . . . . . . . . . . . . . . . . . . . 28
2.5 UV-vis spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.6 Raman spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.7 Temperature programmed reduction and oxidation . . . . . . . . . . . . 33
2.8 Catalytic tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3 Synthesis of silica-supported vanadia catalysts 37
vii
Contents
3.1 Synthesis of SBA-15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.2 Multi-step procedure with functionalization and ion exchange . . . . . . 40
3.3 Incipient wetness impregnation . . . . . . . . . . . . . . . . . . . . . . . . 42
4 Characterization of silica-supported vanadia catalysts 45
4.1 Physical characterization of silica supports . . . . . . . . . . . . . . . . . 45
4.1.1 SBA-15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.1.2 Aerosil 300 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.2 Mechanical, thermal, and hydrothermal stability . . . . . . . . . . . . . . 50
4.2.1 Mechanical stability . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.2.2 Thermal stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
4.2.3 Hydrothermal stability . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.2.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.3 Comparison of silica supports and synthesis methods . . . . . . . . . . . 65
4.3.1 Physical characterization . . . . . . . . . . . . . . . . . . . . . . . . 66
4.3.2 Spectroscopic characterization . . . . . . . . . . . . . . . . . . . . 68
4.3.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
5 Reactivity of silica-supported vanadia catalysts 75
5.1 Catalytic tests after mechanical treatment . . . . . . . . . . . . . . . . . . 75
5.2 Reactivity of di erent silica supports and synthesis methods . . . . . . . 77
5.2.1 Temperature programmed reduction and oxidation . . . . . . . . 77
5.2.2 Catalytic tests . . . . . . . . . . 81
5.2.3 Conclusion and outlook . . . . . . . . . . . . . . . . . . . 85
6 Characterization and catalytic tests of V/Ti-supported SBA-15 catalysts 89
6.1 Characterization of Ti-supported SBA-15 with di erent loadings . . . . 90
6.2 Characterization and catalytic tests of V/Ti-supported SBA-15 . . . . . 95
7 Conclusion and outlook 103
Contents
List of Figures 109
List of Tables 115
A Appendix 131
A.1 Curriculum Vitae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
A.2 Publication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
 Rev. Type: -
 Identifiers: eDoc: 434944
URI: http://dx.doi.org/10.14279/depositonce-2114
URN: urn:nbn:de:kobv:83-opus-21564
 Degree: PhD

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