| Tartalmi leírás: |
PtZSM-5 and PtY catalysts were prepared by the wet ion-exchange
method
from their Na-forms. The modified zeolites were reduced by
either NaBH,
or gaseous H, Reduction with NaBH, did not alter the original
Lewis
acidity of the samples (Lewis acidity due to the sodium ions),
while
reduction with H, generated new Bronsted and Lewis acid sites.
Reduction with NaBH, did not modify the ZSM-5 crystal lattice,
however,
treatment with H-2 led to some structural decomposition. Thus,
Lewis
sites due to extraframework alumina and Bronsted sites due to
hydroxyl
groups of the heeled defect sites were formed. For the Y
zeolite, after
reduction the platinum atoms moved out from the ion-exchange
positions
and started to migrate toward the supercage. On their way they
aggregated and the large crystallites pushed apart portions of
the
zeolite crystal. The detrimental effect was of a higher extent
when
reduction occurred with gaseous H-2. The resulting SiO2-Al2O3
supported
catalyst contained many "true" Lewis sites due to extraframework
alumina species as well as acidic OH groups connected to defect
sites,
however, it has lost shape-selective properties connected to the
zeolitic structure.
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| Azonosító: |
Tamasi, A. and Niesz, K. and Pálinkó, István and Guczi, László and Kiricsi, Imre (2002) Modifying the acidic properties of PtZSM-5 and PtY zeolites by appropriately varying reduction methods. STUDIES IN SURFACE SCIENCE AND CATALYSIS, 142. pp. 1801-1808. ISSN 0167-2991
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