TY  - THES
T1  - Structural dynamics of chlorinated ruthenium dioxide model catalysts under reaction conditions
A1  - Hofmann,Jan Philipp
Y1  - 2010/02/03
N2  - The complex interactions of Cl, O and CO with the RuO2(110) model catalyst surface have been investigated within a mixed approach combining theoretical and several experimental methods. The results have been obtained by density functional theory (DFT) calculations as well as by means of high resolution core level shift spectroscopy (HRCLS), thermal desorption spectroscopy (TDS), Auger electron spectroscopy (AES) and reflection absorption IR spectroscopy (RAIRS). The approach of combining theoretical and experimental methods in catalysis research benefits from the synergism: Interpretative models proposed by theoretical methods are verified by clear-cut experiments and conversely, DFT calculations give helpful advice in the assignment and interpretation of experimental data. 
One of the main topics of the present work was the elucidation of the chlorination mechanism of stoichiometric RuO2(110) by HCl exposure. During the Sumitomo process – the heterogeneously catalysed oxidation of HCl by air - the RuO2 catalyst incorporates chlorine atoms. This surface selective chlorination accounts for the extraordinary stability of the catalyst during the HCl oxidation. Experimental and theoretical studies have been conducted in order to develop a deeper understanding of how the chlorine uptake of the RuO2 catalyst takes place under conditions which are also present in the Sumitomo process.
	The knowledge gained about the chlorination process provided a solid foundation for a further treatment of the properties of the chlorinated RuO2(110) model surface including the interaction with oxygen (important for the HCl oxidation process) and carbon monoxide (CO). In this context, CO was used as a chemically sensitive IR probe molecule, which allowed for a detailed RAIRS analysis of the surface under both ultra high vacuum (UHV) and higher pressure conditions. For that purpose, IR fingerprints of several representative coadsorbate phases of CO with O and Cl on the chlorinated RuO2(110) surface have been obtained under UHV at low temperature. This data was then used in the interpretation of RAIRS spectra obtained under different conditions such as reactions at higher pressure. A very detailed picture of the distribution of chemisorbed CO, O and especially of Cl species under different experimental conditions was gained by exploiting this sensitive technique. 
	Another key issue of the present thesis has been the high degree of mobility of Cl atoms in the complex Cl/O/CO coadsorbate system on the chlorinated RuO2 model catalyst, shown here to dynamically adjust itself in response to the presence of O and CO on the surface under the given experimental conditions. Especially the interplay of chlorine and oxygen atoms (accommodated on the surface) was found to be of decisive importance for an understanding of the stability and dynamic response of the RuO2 catalyst under the conditions of the Sumitomo process. Furthermore, emphasis has been put on the complex pattern of mobility of the Cl atoms, observed to be strongly influenced by the chemical nature of the coadsorbed species (O and CO). The introduction of chlorine atoms as a further component of the RuO2 catalyst induces a change not only in the stability of the oxide but also in its reactivity. 
	In this thesis, special attention will be devoted to the impact of surface chlorination on the activity of the catalyst in a model reaction (in this case CO oxidation) in different pressure regimes. The determination of the influence of Cl substitution with respect to reactivity and stability of the RuO2 catalyst in the CO oxidation may constitute a first necessary step towards a prospective, knowledge-based adjustment of catalytical activity and selectivity of the RuO2 catalyst for more complex oxidation reactions.

KW  - Rutheniumdioxid
KW  - Modellkatalyse
KW  - Chlor
KW  - strukturelle Dynamik
CY  - Gießen
PB  - Universitätsbibliothek
AD  - Otto-Behaghel-Str. 8, 35394 Gießen
UR  - http://geb.uni-giessen.de/geb/volltexte/2010/7411
ER  -