Quantum mechanical modeling of surface reactions in storage catalytic converters [Elektronische Ressource] / presented by Monica Ţuţuianu

Monica

Informations

• Publié par: ruprecht-karls-universitat_heidelberg
• Publié le: 01 janvier 2007
• Nombre de lectures: 11
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

Quantum Mechanical Modeling of Surface Reactions
in Storage Catalytic Converters

INAUGURAL-DISSERTATION

submitted to the

Faculty of Chemistry and Geosciences
of the Rupertus-Carola University of Heidelberg, Germany
for the degree of
Doctor of Natural Sciences


presented by
Monica Ţuţuianu, M. Sc. Chem. Eng.
born in Gala ţi, Romania

Examiners: Prof. Dr. Dr. h. c. Jürgen Warnatz
Prof. Dr. Olaf Deutschmann

thHeidelberg, 13 of July 2007

Interdisziplinäres Zentrum für Wissenschaftliches Rechnen
Ruprecht-Karls-Universität Heidelberg
2007







INAUGURAL-DISSERTATION

submitted to the

Faculty of Chemistry and Geosciences
of the Rupertus-Carola University of Heidelberg, Germany
for the degree of
Doctor of Natural Sciences










presented by
Monica Ţuţuianu, M. Sc. Chem. Eng.
born in Gala ţi, Romania









Quantum Mechanical Modeling of Surface Reactions
in Storage Catalytic Converters
















Examiners: Prof. Dr. Dr. h. c. Jürgen Warnatz
Prof. Dr. Olaf Deutschmann


































To my family







Abstract

Pollutant reduction of internal combustion engines plays an essential role in automotive
industry research and development. Exhaust-gas after-treatment using catalytic converters is
of key importance to this goal. Storage catalytic converters based on barium oxide are a
technology with promising potential to meet current and future emission standards for nitric
oxides (NO ) abatement of lean-burning gasoline and Diesel engines. x
The aim of this work was to develop elementary reaction steps and determine kinetic
parameters for the NO storage reaction mechanism by means of density functional theory x
(DFT). DFT has proven a powerful tool in investigating microscopic aspects of heterogeneous
reactions. Electronic structure calculations were performed for adsorption of different
molecules on two surfaces relevant in automotive exhaust gas purification: barium oxide and
platinum.
The interaction of different species (NO, NO , CO , H O) with the BaO(100) surface was 2 2 2
investigated in terms of adsorption site and adsorption geometry in dependence on surface
coverage. It could be shown that all species form stable adsorbates and adsorption strength
increases in the order NO < H O < NO ≤ CO . It was found that high coverages strongly 2 2 2
reduce the adsorption energy.
Oxygen adsorption, decomposition and diffusion on Pt(111) have been studied. Kinetic
parameters of the reactions of oxygen and the diffusion of atomic oxygen on the surface and
their dependence on surface coverage were determined. It was found that molecular
adsorption of oxygen molecules on a clean surface has a more favorable configuration in the
side-on geometry. The decomposition process is favored at low surface coverages while at
higher coverages it is inhibited. Furthermore, the surface diffusion of atomic oxygen from an
fcc threefold site to a hcp threefold site was investigated. A strong dependence on surface
coverage was observed with activation energies increasing with increasing coverages.
Moreover, the influence of various coadsorbates on surface diffusion of atomic oxygen was

presented. A linear relationship between the coadsorbate’s electronegativity and the reaction
energy was observed.
The kinetic data obtained by DFT investigations were used in a thermodynamic study of
the BaO surface state under realistic operating conditions. Numerical calculations of the
competitive adsorption/desorption equilibria of NO, NO , CO , H O for a typical exhaust gas 2 2 2
composition showed that CO plays an essential role in the surface processes during NO 2 x
storage on BaO. Furthermore, the DFT results obtained were used in a kinetic model of
oxygen surface reaction mechanism on platinum applied in NSR catalysis. The study was
performed in order to better understand the properties of the oxygen spillover reaction as well
as its coupling with surface transport (diffusion).
This thesis presents a detailed quantum chemical study of surface processes relevant in
storage catalytic converters. The study allows a valuable insight into the processes that govern
and potentially limit these types of catalysts.