dc.contributor.advisor | Özensoy, Emrah | |
dc.contributor.author | Emmez, Emre | |
dc.date.accessioned | 2016-01-08T18:15:24Z | |
dc.date.available | 2016-01-08T18:15:24Z | |
dc.date.issued | 2011 | |
dc.identifier.uri | http://hdl.handle.net/11693/15237 | |
dc.description | Ankara : The Department of Chemistry and the Graduate School of Engineering and Science of Bilkent University, 2011. | en_US |
dc.description | Thesis (Master's) -- Bilkent University, 2011. | en_US |
dc.description | Includes bibliographical references leaves 95-99. | en_US |
dc.description.abstract | In this work, formation anddecomposition pathways of of Ba(NO3)2 on BaOBaO2
/Pt(111) surfaces were investigated at the molecular levelfordifferent BaOBaO2coverages
starting from small 2D islands of 0.5 MLE (MLE: monolayer
equivalent) to thick multilayers of 10 MLE via temperature-programmed desorption
(TPD), and X-ray Photoelectron Spectroscopy (XPS) and Low Energy Electron
Diffraction (LEED). BaOxoverlayerswith a surface coverage of ~ 1 MLEreveallong
range ordering with (2×2) and/or (1×2) structures while BaOx films with a surface
coverage of1.5 MLEyields aBaO(110) termination and thicker films ( ≥ 5 MLE)
were observed to be amorphous. Saturation of thick (10 MLE) BaOxoverlayers with
NO2 leads to the formation of nitrates. Nitrate thermal decomposition was
demonstrated to proceed through nitrite intermediates. In TPD experimentstwo major
pathwaysfornitrate decomposition were observed: 1) nitrate decomposition yielding
only NO evolutionat ~650 K, and 2) nitrate decomposition withNO + O2evolutionat
~700 K. This multi-step decomposition behavior was explained by BaO2 formation
during the first stage. The influence of the BaOxdeposition method on the
morphology of the BaOxoverlayers were established: when a thick BaOx layer is
prepared using NO2 for Ba oxidation, BaOx overlayer efficiently wets the Pt(111) substrate forming a well-dispersed film. On the other hand, ifa thick BaOx layer is
heated in O2 (to 873 K), BaOx overlayer agglomerates into 3D clusters, resulting in
the formation of exposed (uncovered) Pt sites. BaOxoverlayers with uncoveredPt
sitescan be “cured” by nitration – thermal decomposition procedures. When the BaOx
layer coverage is below 2.5 MLE, nitrate decomposition temperature is observed at
significantly lower temperatures, demonstrating the catalytic influence of the Pt sites
facilitating the nitrate decomposition. It is proposed that initially, Ba(NO3)2
decomposesatthe boundary/peripheralsites of the Pt/BaOx interface, followed by the
nitrate decomposition originating from 2D BaOx islands, and eventually from the 3D
BaOx agglomerates.
Catalytic deactivation of TiO2-promoted NOx-storage reduction (NSR)
catalysts due to thermal aging effects was investigated using a BaO/TiO2/Pt(111)
model catalyst system. At room temperature, metallic Ba overlayers on TiO2/Pt(111)
was found to be very reactive towards oxide ions on TiO2/Pt(111) resulting in the
formation of BaOx and partial reduction of TiO2. Ba films adsorbed on TiO2/Pt(111)
that are further oxidized in O2 at 523 K lead to BaO and BaO2 surface domains which
can efficiently adsorb both NO2 and CO2. Thermal treatment of BaOBaO2/TiO2/Pt(111)
surface at T ≥ 300 K leads to a monotonic decrease in the
surface Ba/Ti atomic ratio indicating the diffusion of BaO-BaO2 domains into the
underlying TiO2 framework. Solid state reactions between BaOx and TiO2
particularly within 473-873K facilitate the formation of BaTiO3/Ba2TiO4/BaxTiyOz
overlayers. After oxidation at higher temperatures (T > 873 K), surface becomes Badeficient
and the enrichment of the surface with the Ti4+ sites results in a TiO2-
terminated surface. Diffusion of BaOx into the TiO2 matrix and the enrichment of the
surface with Ti sites drastically suppress the NO2 and CO2 adsorption/storage
capacity of the model NOx storage system. These results reveal a direct evidence for
the structural changes associated with the thermal deactivation of TiO2-promoted
NSR catalysts. | en_US |
dc.description.statementofresponsibility | Emmez, Emre | en_US |
dc.format.extent | xvii, 99 leaves, illustrations | en_US |
dc.language.iso | English | en_US |
dc.rights | info:eu-repo/semantics/openAccess | en_US |
dc.subject | NSR | en_US |
dc.subject | Model catalyst | en_US |
dc.subject | BaO thin films | en_US |
dc.subject | TiO2 thin films | en_US |
dc.subject | NO2 | en_US |
dc.subject | UHV | en_US |
dc.subject | BaOx / Pt(111) | en_US |
dc.subject | BaOx/ TiO2/ Pt(111) | en_US |
dc.subject | XPS | en_US |
dc.subject | TPD | en_US |
dc.subject | LEED | en_US |
dc.subject.lcc | QD181.N1 E55 2011 | en_US |
dc.subject.lcsh | Nitrogene oxides. | en_US |
dc.subject.lcsh | Oxidation. | en_US |
dc.subject.lcsh | Catalysis. | en_US |
dc.subject.lcsh | Thin films. | en_US |
dc.title | BaOx/ Pt(111) AND BaOx/ TiO2/ Pt(111) MODEL CATALYSTS
FOR UNDERSTANDING NOx STORAGE-REDUCTION (NSR)
CATALYSIS AT THE MOLECULAR LEVEL | en_US |
dc.type | Thesis | en_US |
dc.department | Department of Chemistry | en_US |
dc.publisher | Bilkent University | en_US |
dc.description.degree | M.S. | en_US |
dc.identifier.itemid | B129725 | |