DARWIN Digitale Dissertationen German Version Strich

FU Berlin
Digitale Dissertation

Yvonne Joseph :
Spectroscopic investigations on the surface chemistry of single crystalline iron oxide films
Spektroskopische Untersuchungen zur Oberflächenchemie von einkristallinen Eisenoxidfilmen

 FU Logo

|Abstract| |Table of Contents| |More Information|

Abstract

Industrially, styrene production is carried out on potassium promoted iron oxide catalysts from ethylbenzene in the presence of steam. Despite the huge amount of styrene produced each year for polystyrene applications nearly nothing is known of the reaction mechanism or the active sites of the catalysts. In order to elucidate the interaction between the catalyst and the educt and product molecules, epitaxial unpromoted and potassium promoted iron oxide model catalyst films were grown on Pt(111) single crystals. The unpromoted films FeO(111), Fe3O4(111) and alpha-Fe2O3(0001) as well as the potassium promoted films KxFe22O34(0001) and KFeO2 were prepared. The geometric structure of the surfaces were monitored with low energy electron diffaction including spot profile analysis (SPA-LEED). The chemical composition of the unpromoted films were characterized by photoelectron spectroscopy (UPS/XPS) and near edge X-ray absorption fine structure specstroscopy (NEXAFS). All spectra of Fe3O4(111) and alpha-Fe2O3(0001) agree well with spectra from iron oxide single crystals, whereas the spectra of the FeO(111) film are slightly different from spectra of single crystals, because the only two bilayer thick FeO(111)-film could not develop bulk properties. The phase composition and the formation of potassium promoted model catalysts were, for the first time, investgated in detail with XPS. The adsorption of ethylbenzene, styrene, and water on the unpromoted films was also investigated with UPS and NEXAFS techniques. When possible, thermodynamic and kinetic parameters were determined from adsorption isobars. The adsorption studies reveal the importance of the Lewis acidity of the iron centers in the near surface region interacting with the Lewis basic adsorbate molecules. This interaction results in a eta6 like adsorption geometry of the phenyl ring of the aromatic molecules on Fe3O4(111) and alpha-Fe2O3(0001) and dissociation of water on Fe3O4(111). On FeO(111) the limited influence of the iron center results only in physisorption. The measured isosteric heats of adsorption are in good agreement with desorption energies from the literature and they correlate linearly with the iron-oxygen layer distance in the topmost surface region. Finally, a reaction mechanism for the ethylbenzene dehydrogenation over unpromoted iron oxide catalysts is proposed.

Table of Contents

Download the whole PhDthesis as a zip-tar file or as zip-File

For download in PDF format click the chapter title

Titelseite, Inhaltsverzeichnis
1. Motivation 1
1.1. Katalyse 1
1.2. Oberflächenphysik 4
1.3. Modellkatalytischer Ansatz 5
1.4. Vorarbeiten und Vorgehensweise 7
2. Physikalische Grundlagen 9
2.1. Adsorption und Desorption 10
2.1.1 Thermodynamik 11
2.1.2 Kinetik nach Langmuir 12
2.1.3 Kinetik nach Kisliuk 14
2.2. Meßmethoden und Datenauswertung 15
2.2.1 Beugung langsamer Elektonen (LEED) 16
2.2.2 Photoelektronenspektroskopie (UPS/XPS) 17
2.2.3 Röntgenabsorption an der Nahkante (NEXAFS) 22
3. Experimentelle Grundlagen 27
3.1. Probenaufbau 27
3.2. Die UHV-Kammern 28
3.2.1 PS-Kammern 28
3.2.2 NEXAFS-Kammer 29
3.2.3 in situ-Kammer 30
4. Chemische Grundlagen 31
4.1. Substrate 31
4.1.1 Eisen-Sauerstoff-Verbindungen 31
4.1.2 Kalium-Eisen-Sauerstoff-Verbindungen 37
4.2 Säure-Base-Theorien 39
4.3 Adsorbate 40
4.3.1 Wasser 40
4.3.2 Ethylbenzol und Styrol 41
5. Substratpräparation und -charakterisierung 43
5.1. Präparation 43
5.1.1 Unpromotierte Eisenoxidfilme 43
5.1.2 Kaliumpromotierte Eisenoxidfilme 45
5.2 Charakterisierung 46
5.2.1 Beugung langsamer Elektronen (LEED) 46
5.2.2 Photoelektronenspektroskopie (UPS/XPS) 47
5.2.3 Röntgenabsorption an der Nahkante (NEXAFS) 62
6. Adsorptionsmessungen 67
6.1. Wasser 67
6.1.1 Photoelektronenspektroskopie (UPS/XPS) 67
6.1.2 Röntgenabsorption an der Nahkante (NEXAFS) 87
6.2. Ethylbenzol 93
6.2.1 Photoelektronenspektroskopie (UPS/XPS) 93
6.2.2 Röntgenabsorption an der Nahkante (NEXAFS) 94
6.3. Styrol 99
6.3.1 Photoelektronenspektroskopie (UPS/XPS) 99
6.3.2 Röntgenabsorption an der Nahkante (NEXAFS) 104
6.4. Fazit 107
6.4.1 Oberflächenphysik 107
6.4.2 Styrolsynthese 109
7. Zusammenfassung 111
Literaturverzeichnis 113

More Information:

Online available: http://www.diss.fu-berlin.de/2001/209/indexe.html
Language of PhDThesis: german
Keywords: catalysis, chemisorption, photoelectron spectroscopy, x-ray absorption, water, ethylbenzene, styrene, iron oxide
DNB-Sachgruppe: 30 Chemie
Date of disputation: 26-Oct-2001
PhDThesis from: Fachbereich Biologie, Chemie, Pharmazie, Freie Universität Berlin
First Referee: Prof. Dr. Robert Schlögl
Second Referee: Prof. Dr. Klaus Christmann
Contact (Author): Yvonne.Joseph@epost.de
Contact (Advisor): schloegl@fhi-berlin.mpg.de
Date created:29-Oct-2001
Date available:12-Nov-2001

 

|| DARWIN|| Digitale Dissertationen || Dissertation|| German Version|| FU Berlin|| Seitenanfang ||

Mail-Icon Fragen und Kommentare an:
darwin@inf.fu-berlin.de

© Freie Universität Berlin 1999