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Surface science studies of model oxide catalysts: Molybdenum oxide on single crystal iron oxide

Bamroongwongdee, Chanut 2010. Surface science studies of model oxide catalysts: Molybdenum oxide on single crystal iron oxide. PhD Thesis, Cardiff University.

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Abstract

This thesis is concerned with the study of molybdenum oxide layer deposited on a single crystal iron oxide substrate. The surface structure of an iron oxide single crystal was investigated by X-ray photoelectron (XPS), low-energy He+-ion scattering (LEIS), low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). XPS measurement reveals the presence of both Fe2+ and Fe3* oxidation states. LEED and STM results obtained from this surface were consistent with a formation of an Fe304(III) surface termination. LEED pattern and STM images reveal an hexagonal array with a periodicity of 6 A and steps in multiples of 5 A. LEIS result shows the presence of both Fe and O in the topmost layer. Well ordered epitaxial molybdenum oxide films were grown on iron oxide single crystal substrates. Their surface structure, morphology and composition were characterized by XPS, LEIS, LEED, and STM. They were prepared by depositing molybdenum oxide onto the substrate and then oxidizing it in 10'7 mbar of oxygen. In the sub-monolayer regime, molybdenum oxide formed islands of ordered structure. XPS measurement yields a Mo 3dsn binding energy consistent with the presence of Mo6*. High resolution STM images reveal a large hexagonal lattice of protrusions with a 12 A periodicity. This pattern is consistent with a p(4x4) structure. At the monolayer coverage, a (23 x 23 )R30 surface structure is produced by annealing in oxygen (107 mbar) at 973 K. STM topographies show clear hexagonal distribution with the period of 1.1 nm corresponding to the pattern observed in LEED. These results suggest that molybdenum oxide may interact with Fe304(III) to form iron molybdate which is stable on the surface.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
ISBN: 9781303218286
Funders: Thai Government Science and Technology Scholarship, Ministry of Science and Technology
Date of First Compliant Deposit: 30 March 2016
Last Modified: 09 Jan 2018 20:30
URI: http://orca-mwe.cf.ac.uk/id/eprint/54989

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