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Tytuł:
Desilication of highly siliceous zeolite ZSM-5 with NaOH and NaOH/tetrabutylamine hydroxide
Autorzy:
Tarach, Karolina
Martínez Triguero, Joaquín
Datka, Jerzy
Rey, Fernando
Drozdek, Marek
Góra-Marek, Kinga
Kuśtrowski, Piotr
Opis:
The results of both chemical and XPS analysis pointed out that desilication of highly siliceous ZSM-5 of Si/Al = 164 was more effective in the surface zone than in the bulk, contrary to zeolite ZSM-5 of Si/Al = 31.6. According to the IR studies in parent zeolite the concentration of protonic sites was very close to the concentration of Al indicating that all Al atoms can form Si-OH-Al. The results of our quantitative IR studies strongly support the realumination thesis, i.e. some Al atoms extracted in basic solutions are subsequently reinserted forming new acidic hydroxyls. In desilicated zeolites all Al atoms were able to form protonic sites, however part of them dehydroxylated during the activation of zeolite producing Lewis acid sites according to the stoichiometry: one protonic site was transformed into one Lewis site. Low temperature nitrogen adsorption revealed that the alkaline treatment of highly siliceous zeolite with 0.2 M NaOH/TBAOH mixture produced mesopores of smaller diameter and narrower pore size distribution than in the case of zeolite of medium Si/Al ratio. This result can be explained by low concentration of Al which similarly as TBA+ cations plays the role of pore directing agents (PDA). Contrary to TBA+, the presence of Al in desilication mixture, led to the formation of larger pores. Therefore, in highly siliceous zeolite TBA + played dominant role as PDA producing narrower pores. Highly siliceous zeolite with uniform distribution of relatively narrow pores may be useful catalyst or catalyst support. The influence of desilication temperature on porosity development was also investigated. The increase of desilication temperature from 338 to 353 K resulted in both more extensive demetalation (more Si and Al is extracted) and the distinct increase of the volume and surface of mesopores. Both lower concentration of protonic sites and higher concentration of Lewis sites confirmed partial zeolite destruction upon desilication at elevated temperature. The experiments of pivalonitrile sorption followed by IR spectroscopy showed a significant increase of accessibility of acid sites to bulky pivalonitrile molecules.
Dostawca treści:
Repozytorium Uniwersytetu Jagiellońskiego
Artykuł
Tytuł:
Tailored approach for hierarchization of all-silica zeolites
Autorzy:
Tarach, Karolina
Smoliło-Utrata, Małgorzata
Gackowski, Mariusz
Rey, Fernando
Słowik, Grzegorz
Valencia, Susana
Góra-Marek, Kinga
Opis:
Adding secondary mesoporosity to all-silica zeolites can improve mass transfer, potentially leading to new applications in catalysis and separation. The tailored post-synthesis methods involving detemplation, desilication, and application of pore-directing agents were applied to examine the influence of zeolite type structure, crystal properties, and synthesis conditions on the hierarchization feasibility of all-silica ITQ-29 (LTA), silicalite-1 (MFI), silicalite-2 (MEL), and beta (*BEA) zeolites. Advanced characterization tools such as rapid scan RS FT-IR spectroscopy, field emission scanning electron microscopy, and focused ion beam provided insight into the properties of hierarchical all-silica zeolites. The formation of hierarchical all-silica zeolites was found to be pore size and shape-dependent and defects-oriented; however, the ultimate influence of these factors on hierarchization is interdependent.
Dostawca treści:
Repozytorium Uniwersytetu Jagiellońskiego
Artykuł
Tytuł:
Hierarchical mordenite dedicated to the fluid catalytic cracking process : catalytic performance regarding textural and acidic properties
Autorzy:
Tarach, Karolina
Martinez-Triguero, Joaquin
Liu, Lichen
Tekla, Justyna
Rey, Fernando
Kuśtrowski, Piotr
Góra-Marek, Kinga
Olejniczak, Zbigniew
Opis:
This work was attempted to show that the sequential dealumination and desilication with the use of tetraalkylammonium cations as pore directing agents (PDA) are an effective procedure for the fabrication of hierarchical mordenite zeolites with preserved crystallinity and uniform intracrystalline mesoporosity. Additionally it was demonstrated that desilication performed in the presence of PDAs offered greater mesoporosity development when compared to pure NaOH treatment. IR studies employing ammonia and pyridine as probes exhibited considerably Brønsted acidity of the resulting materials. The strength of protonic sites was reduced upon the treatment; nevertheless their accessibility to hindered 2,6-di-tert-butylpyridine molecules became noticeably high owing to a more open hierarchical structure. Concentration of the acid sites, their strength, and accessibility were reflected in both catalytic activity and selectivity in the cracking of n-decane, 1,3,5-tri-isopropylbenzene, and vacuum gas oil.
Dostawca treści:
Repozytorium Uniwersytetu Jagiellońskiego
Artykuł
Wyświetlanie 1-10 z 14

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