TY  - THES
AB  - Spinels are highly catalytically effective already at low temperatures and serve as catalyst in many reactions because of their high redox ability.
The spinel lattice permits high defect concentrations, so that doping strategy can be employed to tune its physicochemical properties. The present study focuses on the exploitation of the chemical vapor deposition process (CVD) as a rational preparation method for the investigation of monolithic and planar model catalysts. Co3O4 is a spinel that has been identified as a very promising catalytic material for deep oxidation reactions. Doping the spinel structure of cobalt oxide with zinc was achieved in the first stages of this study using conventional dual-precursor source CVD, but controlling the zinc concentration failed because of highly contrasting sticking coefficients of the used metal precursors. In order to increase the sticking coefficient of zinc, the CVD method was modified and combined with a Direct Liquid Injection (DLI) method and pulsed injection. The Pulsed Spray Evaporation CVD method (PSE-CVD), built up in this work, was optimized and tested on pure and with zinc or chrome doped Co3O4 films.
The deposited thin films exhibited no contamination with other crystalline phases even when high M/Co ratios (>0.5) were attained. Using the new constructed deposition method, it was possible to grow pure and doped cobalt spinel layers on glass and metal substrates based on a mixture of acetylacetonates used as metal precursors, dissolved in ethanol. Zinc and chrome-doped layers were deposited successfully with growth rates (GR) between 1 and 2 nm/min at a reactor temperature of 500 °C. Doped layers were characterized using several analytical techniques including XRD, EDX and REM.
The vibrational frequencies of the spinel lattice were observed using in situ IRES (Infrared Emission Spectra) and IRAS (Infrared Reflection Spectra) techniques. The thermal stability of Co3O4 and doped layers as thin films was measured with in-situ IRES (Infrared Emission Spectra).
According to the Mars-van-Krevelen mechanism, catalysts need available oxygen iones to participate in catalytic reaction. O2--ions are donated to oxidize the reactant while the reduced catalyst is reoxidized afterwards. For this reason, redox ability of the catalyst (reducibility and re-oxidability) is investigated seperately using in situ IRES.
Conductivity of a lattice shows the quantity or stability of defects in the structure. Co3O4 is a p-type semiconductor, where the lack of O2--ions (hole, defect) cause a positive charge carrier. In these investigations a specific conductivity of the layers was measured according to the four point method.
In this thesis a new preparation method of pure and doped cobalt spinel layers was successfully established. The PSE-CVD is shown to be a highly suitable rational method for the deposition of thin layers with controlled stoichiometry and phase structures. This simplifies the detailed investigation of catalytic materials either in model-planar or as practical monolithic form.
In situ emission FTIR measurement (IRES) represents a very sensitive method for the evaluation of the thermal behavior of solid materials. Thus it was possible for the first time to observe and evaluate reduction and oxidation procedures of catalytic layers during the reactions. This new analyzing process, which was well constructed and tested in the present work, allows an accurate investigation of the thermal characteristics of planar model catalysts with small surface areas.
DA  - 2008
KW  - Tricobalttetraoxid , Spinellstruktur , CVD-Verfahren , Einspritzung , Ausgangsmaterial , MCM-Katalysator , Zink , Chrom , Röntgendiffraktometrie , Kobaltoxid-Spinellstruktur , Pulsed Spray Evaporation CVD (PSE-CVD) , Dotierung mit Zink/Chrom , Planare Modell-Katalysatoren, In situ Emissions-IR , Cobalt oxide spinel structure , Pulsed Spray Evaporation CVD (PSE-CVD) , Doping with zinc/chrome , Planar model catalysts , In situ emission IR
LA  - ger
PY  - 2008
TI  - Dotierung der Spinellstruktur von Kobaltoxid-Dünnschichten und deren Auswirkungen auf die physikalisch-chemischen Eigenschaften
UR  - https://nbn-resolving.org/urn:nbn:de:hbz:361-14650
Y2  - 2024-11-21T21:40:37
ER  -