The influence of metal oxide additives on the molecular structures of surface tungsten oxide species on alumina. II. In situ conditions

The dehydrated Raman spectra of unpromoted WO 3/Al 2O 3 indicate that the tungsten oxide surface species have the mono-oxo structure and are present as tetrahedrally coordinated monomers at low loadings and as a mixture of tetrahedrally and octahedrally coordinated surface polymers at high loadings....

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Bibliographic Details
Published inJournal of molecular catalysis. A, Chemical Vol. 132; no. 1; pp. 59 - 71
Main Authors Ostromecki, Marlene M., Burcham, Loyd J., Wachs, Israel E.
Format Journal Article
LanguageEnglish
Published Amsterdam Elsevier B.V 28.05.1998
Elsevier
Subjects
Catalysis
Catalysts: preparations and properties
Chemistry
Exact sciences and technology
General and physical chemistry
In situ Raman spectroscopy
Secondary metal oxide additives
Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
Tungsten oxide
Tungsten oxide
In situ Raman spectroscopy
Secondary metal oxide additives
Heterogeneous catalysis
Binary compound
Molecular structure
Transition metal Compounds
In situ
Tungsten Oxides
Modified catalyst
Raman spectrometry
Metal Oxides
Experimental study
Alumina
Supported catalyst
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Summary:The dehydrated Raman spectra of unpromoted WO 3/Al 2O 3 indicate that the tungsten oxide surface species have the mono-oxo structure and are present as tetrahedrally coordinated monomers at low loadings and as a mixture of tetrahedrally and octahedrally coordinated surface polymers at high loadings. The effect of introducing secondary metal oxide additives to WO 3/Al 2O 3 catalysts, where tungsten oxide is present as a two-dimensional surface metal oxide overlayer, was investigated with in situ Raman spectroscopy under dehydrated conditions. The secondary metal oxide additives P 2O 5, SnO 2, Fe 2O 3, NiO, ZnO, CoO, CeO 2 and MgO coordinate directly to the oxide support without significantly interacting with the surface tungsten oxide phase. The secondary metal oxide additives La 2O 3, CaO, K 2O and Na 2O directly interact with surface tungsten oxide species to form both a surface mixed metal oxide complex and, for La 2O 3 and CaO, a crystalline tungstate compound. The noninteracting additives tend to be acidic (P 2O 5 and SnO 2) or mildly basic (Fe 2O 3, NiO, ZnO, CoO, CeO 2 and MgO) and the interacting additives tend to be more basic (La 2O 3, CaO, K 2O and Na 2O).
ISSN:1381-1169
1873-314X
DOI:10.1016/S1381-1169(97)00227-6