Structure, Morphology, and Catalytic Properties of CuO_x/CeO₂ Model Catalysts

Abstract

Cerium dioxide, or ceria, is a chemically stable oxygen ion conducting material with a capacity to store and release oxygen, and is therefore extensively used in combustion catalysts. The Cu-Ce-O system has been identified as one of the most active catalysts for the combustion of carbon monoxide. To study the catalytic oxidation of CO, we have synthesised model CuO_x/CeO₂ catalysts by gas phase techniques.



PVD rf-magnetron sputtering was used to produce thin film catalysts. Inert gas condensation (IGC) with multiple thermal heating sources was employed to produce nanocomposite particles. This allowed us also to study the growth of thin films and particles, respectively. The catalysts were characterised by a powerful complementary combination of methods, combining small-area and whole-sample characterisation of local structure and long-range order; High resolution electron microscopy, atomic force microscopy, nitrogen adsorption, and analytical X-ray techniques, such as energy-dispersive spectroscopy, and photoelectron spectroscopy. High-energy diffraction, and X-ray absorption fine structure spectroscopy using synchrotron radiation were employed to collect information on crystallinity and the local environment of Cu.



The thin CeO₂ films grown on surfaces of á-Al₂O₃ formed extremely sharp ridges exposing exclusively {111}-type surfaces despite the nominally (001)-orientation. We found that a well-defined portion of (001) could be created by annealing. Thin layers of CuO_x were deposited on top of both the as-prepared and annealed ceria thin films. The annealed films with copper on top exhibit a markedly higher activity than the others, indicating a favourable synergistic effect between the copper oxide and CeO₂(100) surfaces (i.e. catalytic anisotropy). In addition, it was realised that the as-prepared films are excellent for quickly evaluating AFM tips (i.e. as tip characteriser), and for studying artefacts and tip-sample phenomena occurring during tapping mode AFM imaging. Nanocomposite CuO_x/CeO₂ particles were produced over the whole compositional range. A change of the copper content clearly altered the nanostructured morphology, forming e.g. crust structures between 30 and 70 at.% Cu. A growth mechanism for the formation of crust structures is suggested. The dispersion of copper that controls the number of active sites and, hence, the catalytic activity was shown to be dependent on the: <i>i</i>) total copper content, <i>ii</i>) the nanostructured morphology, and <i>iii</i>) the crystallinity of ceria. A copper content between 5 and 30 at.% Cu was found to be beneficial for the combustion of carbon monoxide.

• author: Skårman, Björn
• supervisor: [unknown] [unknown]
• opponent: Dr Hansen, Poul L., Haldor Topsøe A/S, Lyngby, Denmark
• organization: Centre for Analysis and Synthesis
• publishing date: 2002
• type: Thesis
• publication status: published
• subject: Chemical Sciences
• keywords: Synchrotron radiation, High-energy Diffraction, X-ray Absorption Fine Structure Spectroscopy., Chemical technology and engineering, Kemiteknik och kemisk teknologi, Chemistry, Kemi, Material technology, Materiallära, materialteknik, X-ray photoelectron spectroscopy, Atomic force microscopy, Gatan Image Filter (GIF), Energy-filtered TEM, High-resolution electron microscopy, Inert gas condensation (IGC), rf Magnetron sputtering, Thermal activation, Batch reactor, Carbon monoxide oxidation, Surface sensitivity, Catalytic anisotropy, Growth, Nucleation, Topography, Roughness, Core-shell structures, Morphology, Nanostructured, Nanocomposite, Nanoparticles, Surface structure, Polycrystalline surfaces, Thin films, Copper oxide, Cerium dioxide (CeO2), Ceria
• pages: 126 pages
• defense location: Chemical Center K:D, Lund
• defense date: 2002-03-22 13:15:00
• ISBN: 91-628-5123-3
• language: English
• LU publication?: yes
• additional info: Article: S. N. Jacobsen, U. Helmersson, R. Erlandsson, B. Skårman, L. R. Wallenberg.Sharp Microfacetting of (001)-Oriented Cerium Dioxide Thin Films and the Effect of Annealing on Surface MorphologySurf. Sci. 429(1999)22-33. Article: B. Skårman, L. R. Wallenberg, S. N. Jacobsen, U. Helmersson, C. Thelander.High Resolution Imaging of TappingMode® AFM Probes and the Use of a Well-Ordered CeO2 Thin Film with Atomically Sharp Ridges as Tip CharacteriserLangmuir 16(2000)6267-6277. Article: B. Skårman, L. R. Wallenberg, P.-O. Larsson, A. Andersson, S. N. Jacobsen, U. Helmersson.Carbon Monoxide Oxidation on Copper Oxide Thin Films Supported on Corrugated Cerium Dioxide {111} and {001} SurfacesJ. Catal. 181(1999)6-15. Article: B. Skårman, T. Nakayama, D. Grandjean, R. E. Benfield, E. Olsson, K. Niihara, L. R. Wallenberg.Morphology and Structure of CuOx/CeO2 Nanocomposite Catalysts Produced by Inert Gas Condensation: an HREM, XPS and High-Energy Diffraction StudySubmitted to Chem. Mater. (Dec. 2001). Article: B. Skårman, D. Grandjean, R. Benfield, A. Hinz, A. Andersson, L. R. Wallenberg.Carbon Monoxide Oxidation on CuOx/CeO2 Nanocomposite Particles Characterised by HRTEM, XPS, XAS, and High-Energy DiffractionSubmitted to J. Catal. (Feb. 2002). The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Polymer and Materials Chemistry (LTH) (011001041)
• id: 1e67643d-e838-4c23-9193-8c176a831629 (old id 464413)
• date added to LUP: 2016-04-04 11:06:34
• date last changed: 2018-11-21 21:02:42