| Autor: |
Efim S. Shpiro, R. V. Dmitriev, Olga P. Tkachenko, D.P. Shevchenko |
| Rok vydání: |
1994 |
| Předmět: |
|
| Zdroj: |
Applied Catalysis A: General. 107:147-164 |
| ISSN: |
0926-860X |
| DOI: |
10.1016/0926-860x(94)85152-2 |
| Popis: |
X-ray photoelectron spectroscopy (XPS), infrared (IR), electron microscopy (EM) and energy dispersive X-ray (EDAX) studies of in various ways prepared Ga/H-ZSM-5, Pt-Ga/H-ZSM-5 as well as Ga-silicate and Pt/Ga-silicate have been performed. The external surface of the zeolite crystal was originally strongly enriched with a Ga2O3 phase the dispersion of which depends on the preparation as well. Ga reduction, evidenced by XPS Ga 3d line shifts, occurred during reduction and/or the reaction mixture treatment and it was accompanied by migration of GaI cations into the zeolite channels. The migration of unreduced GaIII species via solid-state reactions is less pronounced. The gallium reduction and migration is dramatically promoted by platinum introduced into both Ga/H-ZSM-5 and Ga-silicate; the reduction degree in the last sample is limited by the concentration of the extra-framework GaIII ions. Platinum was shown to be finely dispersed in highly acidic Pt-Ga/H-ZSM-5 while most of the platinum formed aggregates (30–50A˚) on the external surface of Ga-silicate. IR of adsorbed hydrogen and pyridine confirmed that reduction results in the formation of new strong Lewis acidic sites. Along with GaI-HZ and GaIIHZ structures mixed Pt-Ga particles located within the zeolite structure are most likely to be responsible for the dramatic enhancement of the aromatic selectivity found with Pt-Ga/zeolite catalysts (see Part II). |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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