Application of dynamic photoluminescence spectroscopy to the study of the active surfaces sites on supported Mo/SiO sub 2 catalysts. Features of anchored and impregnated catalysts

Journal Article · Wed Nov 22 04:00:00 EST 1989 · Journal of the American Chemical Society; (USA)

DOI:https://doi.org/10.1021/ja00206a004· OSTI ID:7198714

Anpo, Masakazu; Kondo, Masao ^[1]; Coluccia, S ^[2]; Louis, C; Che, M ^[3]

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1. Univ. of Osaka Prefecture (Japan)
2. Universita di Torino (Italy)
3. Universite Pierre et Marie Curie, Paris (France)

A dynamic photoluminescence technique has been applied to investigate the active surface species on two different types of Mo/SiO{sub 2} catalysts, which contain lower Mo content (0.01-0.1 wt % Mo) and differ in molybdenum dispersion. Phosphorescence spectra of the Mo/SiO{sub 2} catalysts, which are attributed to the radiative decay processes from the charge-transfer excited triplet state of tetrahedral dioxo-molybdenum species, appear at {approximately} 440 nm at 298 K and shift to 470 nm at 77 K. The decay curves of the phosphorescence of the anchored and impregnated Mo/SiO{sub 2} catalysts indicate that the anchored catalysts possess only 1 type of Mo emitting site, while the impregnated ones contain at least 2. These results are confirmed by photoluminescence quenching by O{sub 2} or CO, in which the phosphorescence of the anchored catalysts is completely quenched but that of the impregnated samples is only partially quenched. With the anchored catalyst the absolute quenching rate constants of the charge-transfer excited triplet are determined first to be 7.6 {times} 10{sup 7} g of catalyst/mol {times} s for O{sub 2} and 4.2 {times} 10{sup 6} of catalyst mol {times} s for CO, respectively. The phosphorescence spectra of the anchored catalysts obtained at different excitation wavelengths are found to be the same, being quite different from that of impregnated catalysts, where the phosphorescence spectra change in their position with excitation energies. These results indicate that the dynamic photoluminescence technique is useful for investigation not only of active surface species on metal oxides supported on a carrier at very small concentrations but also of their reactivity in the excited states.

• OSTI ID: 7198714
• Journal Information: Journal of the American Chemical Society; (USA), Journal Name: Journal of the American Chemical Society; (USA) Vol. 111:24; ISSN 0002-7863; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360104* -- Metals & Alloys-- Physical Properties
360603 -- Materials-- Properties
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYSTS
CHALCOGENIDES
DATA
DATA ANALYSIS
ELEMENTS
EXPERIMENTAL DATA
INFORMATION
LUMINESCENCE
MEASURING INSTRUMENTS
MEASURING METHODS
METALS
MOLYBDENUM
NONMETALS
NUMERICAL DATA
OXIDES
OXYGEN
OXYGEN COMPOUNDS
PHOTOLUMINESCENCE
QUENCHING
SILICON COMPOUNDS
SILICON OXIDES
SURFACE PROPERTIES
TRANSITION ELEMENTS