Surface active sites of V/sub 2/O/sub 5/-WO/sub 3/ catalysts
The surface active sites of V/sub 2/O/sub 5/-WO/sub 3/ catalysts were investigated by means of secondary ion mass spectrometry (SIMS), IR spectroscopy of adsorbed NH/sub 3/, temperature-programmed desorption (TPD) of NH/sub 3/, and the NARP (NO-NH/sub 3/ rectangular pulse) technique, and the bulk and surface of the catalysts were characterized by means of X-ray diffraction (XRD), IR, electron spin resonance (ESR), and X-ray photoelectron spectroscopy (XPS). Although V/sub 2/O/sub 5/ and WO/sub 3/ are not well-mixed in the bulk of the catalysts, V and W ions are well-mixed in the surface of the catalysts, causing a remarkable promoting effect of WO/sub 3/ on the surface active sites. The surface concentration of the redox sites measured by the NARP technique increased with increasing WO/sub 3/ content, and, at high content of WO/sub 3/, the surface concentration of the redox sites was much larger than the surface concentration of V ions. By means of SIMS, it was verified that the oxygen species bonded to the surface W ions also act as the redox sites in the reduction of NO with NH/sub 3/ at such low temperature that the reaction cannot proceed on WO/sub 3/ itself. It was concluded that the redox sites on V/sub 2/O/sub 5/-WO/sub 3/ catalysts are not only the surface V/double bond/O species but also the surface W/double bond/O species interacting with vanadium ions. As for the acid sites examined by TPD of NH/sub 3/, both the surface concentration and the strength are not changed by the addition of WO/sub 3/.
- Research Organization:
- Nagoya Univ. (Japan)
- OSTI ID:
- 6255274
- Journal Information:
- J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 92:21; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
CATALYSIS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
COHERENT SCATTERING
DATA
DIFFRACTION
ELECTROMAGNETIC RADIATION
ELECTRON SPECTROSCOPY
ELECTRON SPIN RESONANCE
EXPERIMENTAL DATA
INFORMATION
INFRARED SPECTRA
IONIZING RADIATIONS
MAGNETIC RESONANCE
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
PHOTOELECTRON SPECTROSCOPY
RADIATIONS
REFRACTORY METAL COMPOUNDS
RESONANCE
SCATTERING
SPECTRA
SPECTROSCOPY
STRUCTURAL CHEMICAL ANALYSIS
SURFACE PROPERTIES
TRANSITION ELEMENT COMPOUNDS
TUNGSTEN COMPOUNDS
TUNGSTEN OXIDES
VANADIUM COMPOUNDS
VANADIUM OXIDES
X RADIATION
X-RAY DIFFRACTION