PHYSICS/BK21 SEMINAR (08/06/30)
관련링크
본문
"Redox Induced Adsorption Geometry Change of Supported Metal-oxide Catalysts
* Speaker : Dr. Chang-Yong Kim[Canadian Light Source]
* Place : Physics seminar room (Science Bldg. 3-201)
* Date & Time : Jun. 30(Mon.) pm 3:00 ~
* Abstract
Supported metal oxides are among the most important of catalytic materials systems. However, there is a lack of experimental atomic-scale structural information for describing the relevant interfaces. By using x-ray photoemission spectroscopy (XPS) and x-ray standing wave (XSW) measurements, adsorption geometries of vanadium oxides in oxidize and reduced phases have been studied. The V adlayers were prepared on alpha-Fe2O3(0001) and alpha-TiO2(110) surfaces by the MBE and atomic layer deposition (ALD) methods. The oxidation state of the V was measured with the XPS. The XSW analysis results are used to generate a direct-space, model-independent image [1, 2] of the V distribution.
In conjunction with XPS results, the direct-space atomic density profiles reveal that the V occupies high-symmetry surface sites except V5+ on alpha-TiO2(110), and the oxidation state change induces redistribution of vanadium adatom. The vanadium adatoms in oxidized (V5+) and reduced (V3+) phases occupy bulk-like substitution sites on the alpha-Fe2O3(0001) surface as shown in Fig. 1 [3]. The occupation of bulk-like substitution sites has been observed also for the VOX deposited on alpha-TiO2(110) surface, but only in reduced phase (V4+).
The oxidized V5+ does not occupy high-symmetry site but makes bonds with three lattice oxygen atoms of alpha-TiO2(110) surface to form a tetrahedron. Our current results suggest that geometries of the supported vanadium oxides are determined not only by oxidation state of the V but also by surface symmetry of substrate.
Contact Person : Prof. Jinwook Chung(054-279-2071, jwc@postech.ac.kr)"
* Speaker : Dr. Chang-Yong Kim[Canadian Light Source]
* Place : Physics seminar room (Science Bldg. 3-201)
* Date & Time : Jun. 30(Mon.) pm 3:00 ~
* Abstract
Supported metal oxides are among the most important of catalytic materials systems. However, there is a lack of experimental atomic-scale structural information for describing the relevant interfaces. By using x-ray photoemission spectroscopy (XPS) and x-ray standing wave (XSW) measurements, adsorption geometries of vanadium oxides in oxidize and reduced phases have been studied. The V adlayers were prepared on alpha-Fe2O3(0001) and alpha-TiO2(110) surfaces by the MBE and atomic layer deposition (ALD) methods. The oxidation state of the V was measured with the XPS. The XSW analysis results are used to generate a direct-space, model-independent image [1, 2] of the V distribution.
In conjunction with XPS results, the direct-space atomic density profiles reveal that the V occupies high-symmetry surface sites except V5+ on alpha-TiO2(110), and the oxidation state change induces redistribution of vanadium adatom. The vanadium adatoms in oxidized (V5+) and reduced (V3+) phases occupy bulk-like substitution sites on the alpha-Fe2O3(0001) surface as shown in Fig. 1 [3]. The occupation of bulk-like substitution sites has been observed also for the VOX deposited on alpha-TiO2(110) surface, but only in reduced phase (V4+).
The oxidized V5+ does not occupy high-symmetry site but makes bonds with three lattice oxygen atoms of alpha-TiO2(110) surface to form a tetrahedron. Our current results suggest that geometries of the supported vanadium oxides are determined not only by oxidation state of the V but also by surface symmetry of substrate.
Contact Person : Prof. Jinwook Chung(054-279-2071, jwc@postech.ac.kr)"
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