Tungsten catalysts
- Details
- Category: Tungsten Patents
- Published on Tuesday, 22 January 2013 11:21
The present invention relates to a new tungsten-based catalyst on a zirconia and/or titanium dioxide support. At the present time, there is no tungsten/zirconia catalyst which has a high content of tungsten and no additive and which is active after calcination at a temperature less than or in the order of 700° C., or even 600° C.
Various authors indeed propose that the strong acid sites correspond to the formation of micro fields of tungsten trioxide (WO3). This hypothesis allows several experimental observations to be reconciled: the increase in activity with the percentage of tungsten (20% above the most active), the need to heat the solid to a temperature where sintering begins to become evident, as well as the observation in the Raman spectrum of lines which correspond to the clusters of WO3. In some cases, the isolated atoms of tungsten are in a deformed octahedral environment and that there is no tetrahedral tungsten in the case of a tungsten/zirconia solid.
It can be determined from this that current tungsten/zirconia catalysts substantially comprise octahedral tungsten, probably owing to the process of preparation thereof which is based on the use of metatungstates which decompose into WO42− ions only at a very basic pH at which the zirconia does not fix anions.
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