EPR investigation of the coordination sphere of Mo/sup 5 +/ ions on thermally reduced silica-supported molybdenum catalysts prepared by the grafting method

Journal Article · Thu May 21 04:00:00 EDT 1987 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100295a043· OSTI ID:6367979

Louis, C; Che, M

Thermally reduced Mo/SiO/sub 2/ catalysts prepared by the grafting method, i.e., by air- and water-free reaction between MoCl/sub 5/ and hydroxyl groups of silica, present three EPR Mo/sup 5 +/ signals, clearly identified by means of their third-derivative spectrum (g/sub perpendicular/ = 1.944, g/sub parallel/ = 1.892 for Mo/sub 6c//sup 5 +/; g/sub perpendicular/ = 1.957, g/sub parallel/ = 1.866 for Mo/sub 5c//sup 5 +/; and g/sub parallel/ = 1.755 for Mo/sub 4c//sup 5 +/). The coordination sphere of the corresponding species as studied with water and carbon monoxide as probe molecules, which only act as ligands. The transformation of the EPR signals upon water adsorption, the analysis of the superhyperfine structure induced by /sup 13/CO adsorption, as well as the analysis of the various g tensors have led to attribute these signals to molybdenyl ions in tetra-M(Mo/sub 4c//sup 4 +/), penta- Mo/sub 5c//sup 5 +/), and hexacoordination (Mo/sub 6c//sup 5 +/). This is the first positive identification by EPR of surface tetrahedral Mo/sub 4c//sup 5 +/ ions produced by thermal reduction. It has been made possible owing to the high Mo dispersion on the grafted samples. The earlier data found in the literature on the g values of supported Mo/sup 5 +/ ions are rationalized on the basis of the present results.

• Research Organization: Universite P. et M. Curie, Paris, France
• OSTI ID: 6367979
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 91:11; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
CATALYSTS
CATALYTIC EFFECTS
CATIONS
CHALCOGENIDES
CHARGED PARTICLES
COORDINATION NUMBER
DATA
ELECTRON SPIN RESONANCE
ELEMENTS
EXPERIMENTAL DATA
HEAT TREATMENTS
INFORMATION
IONS
MAGNETIC RESONANCE
METALS
MINERALS
MOLYBDENUM
NUMERICAL DATA
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
RESONANCE
SILICA
SILICON COMPOUNDS
SILICON OXIDES
STRUCTURAL CHEMICAL ANALYSIS
TRANSITION ELEMENTS