Interaction chemistry between molybdena and alumina: infrared studies of surface hydroxyl groups and adsorbed carbon dioxide on aluminas modified with molybdate, sulfate, or fluorine anions
The surface OH groups on ..gamma..-Al/sub 2/O/sub 3/ modified with various concentrations of F/sup /minus//, SO/sub 4//sup 2/minus//, or molybdate anions were studied by use of IR techniques as well as by the adsorption of CO/sub 2/ in order to reveal the interaction chemistry between Al/sub 2/O/sub 3/ and molybdate species. Physicochemical characterizations of the modified Al/sub 2/O/sub 3/ were also conducted by means of LRS, XPS, and TPR techniques. It was revealed that the chemical reactivities and surface concentrations of hydroxyl groups determined the interaction modes between the anion and Al/sub 2/O/sub 3/, that is, the dispersion and distribution of the anion and its configuration. The molybdate anions were found to react with basic OH groups in a stoichiometry of OH/sup /minus///Mo = 1 at a concentration of < 10 /times/ 10/sup 13/ Mo cm/sup /minus/2/. It was shown that nonbasic OH groups were simultaneously consumed for anchoring molybdate species in tetrahedral configurations. In this concentration range, the OH/anion ratio was almost identical for SO/sub 4//sup 2/minus// and molybdate anions. With increasing molybdenum content, the OH/Mo ration decreased markedly, resulting in the formation of polymolybdate species. With SO/sub 4//sup 2/minus///Al/sub 2/O/sub 3/ and F/sup /minus///Al/sub 2/O/sub 3/, similar correlations were established between the formation of surface of subsurface species and the concentrations of reactive OH groups. On reduction or sulfurization of the MoO/sub 3//Al/sub 2/O/sub 3/ catalysts, a part of the consumed OH groups was restored and the extent of recovery increased as the wavenumber decreased.
- Research Organization:
- Osaka Univ. (Japan)
- OSTI ID:
- 6189035
- Journal Information:
- J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 92:25; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
ABSORPTION SPECTROSCOPY
ADSORPTION
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
ANIONS
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CATALYSIS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHARGED PARTICLES
CHEMICAL REACTIONS
DATA
ELECTRON SPECTROSCOPY
EXPERIMENTAL DATA
FLUORINE COMPOUNDS
HALOGEN COMPOUNDS
HYDROGEN COMPOUNDS
HYDROXIDES
INFORMATION
INFRARED SPECTRA
IONS
LASER SPECTROSCOPY
MOLYBDATES
MOLYBDENUM COMPOUNDS
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
PHOTOELECTRON SPECTROSCOPY
RAMAN SPECTROSCOPY
REFRACTORY METAL COMPOUNDS
SORPTION
SPECTRA
SPECTROSCOPY
STRUCTURAL CHEMICAL ANALYSIS
SULFATES
SULFUR COMPOUNDS
THERMAL ANALYSIS
TRANSITION ELEMENT COMPOUNDS