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Accessibility of acid sites in hierarchical zeolites : quantitative IR studies of pivalonitrile adsorption


Accessibility of acid sites in hierarchical zeolites : quantitative IR studies of pivalonitrile adsorption

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dc.contributor.author Tarach, Karolina [SAP14004719] pl
dc.contributor.author Góra-Marek, Kinga [SAP11018751] pl
dc.contributor.author Datka, Jerzy [SAP11003748] pl
dc.date.accessioned 2015-01-30T09:42:40Z
dc.date.available 2015-01-30T09:42:40Z
dc.date.issued 2013 pl
dc.identifier.issn 1932-7447 pl
dc.identifier.uri http://ruj.uj.edu.pl/xmlui/handle/item/2827
dc.language eng pl
dc.rights Dodaję tylko opis bibliograficzny *
dc.rights.uri *
dc.title Accessibility of acid sites in hierarchical zeolites : quantitative IR studies of pivalonitrile adsorption pl
dc.type JournalArticle pl
dc.description.physical 9237-9244 pl
dc.description.additional Na publikacji autorka Tarach Karolina podpisana jako Sadowska Karolina. pl
dc.abstract.en Accessibility studies of acid sites in zeolites involving quantitative IR measurements with hindered pivalonitrile as probe molecule were performed. The extinction coefficients of the diagnostic bands of pivalonitrile interacting with Brønsted and Lewis acid sites were determined by using several zeolites structures of different concentrations and acid strength of sites. The accessibility factor (AF) was defined as the ratio of the concentrations of acid sites accessible to pivalonitrile and sites interacting with pyridine. The AF can be applied to both Brønsted and Lewis sites, whereas the methods proposed in previous works were limited only to Brønsted sites. Moreover, this method can also be applied to the accessibility studies of transition-metal cations being active sites in redox reactions. The AF suitability for accessibility studies was investigated for desilicated zeolites HZSM-5 of medium and high Si/Al ratio treated with NaOH and NaOH/ tetrabutylammonium hydroxide. The correlation between the values of mesopore surfaces and AFs for both Brønsted and Lewis sites in highly siliceous zeolites was observed. In more extensively desilicated zeolites, all of the acid sites were accessible to pivalonitrile, that is, AF = 1. Thereby, we assume that pivalonitrile can react not only with sites on external surfaces and in micropore mouths, as generally accepted, but small amounts of pivalonitrile can also migrate inside micropores. In desilicated zeolites with the extended mesopore system smaller fragments of micropores between two mesopores are preserved, which results in shorter average length of micropores. It facilitates the migration of pivalonitrile, and the sites inside micropores became accessible to bulky molecule. The accessibility of Lewis acid sites in desilicated zeolites is even more enhanced than that of Brønsted sites. Taking into consideration the fact that in desilicated zeolites the majority of Lewis sites originate from dehydroxylation of the Si-OH-Al groups, previously formed by the reinsertion of Al extracted from zeolite during alkaline treatment, their high accessibility is reasonable. Those newly formed Lewis sites are situated on mesopore surfaces, which facilitates accessibility to bulky molecules. pl
dc.description.volume 117 pl
dc.description.number 18 pl
dc.identifier.doi 10.1021/jp400400t pl
dc.identifier.eissn 1932-7455 pl
dc.title.journal Journal of Physical Chemistry. C pl
dc.language.container eng pl
dc.affiliation Wydział Chemii : Pracownia Spektrometrii w Podczerwieni pl
dc.affiliation Wydział Chemii : Zakład Chemii Nieorganicznej pl
dc.subtype Article pl
dc.rights.original bez licencji pl
.pointsMNiSW [2013 A]: 35

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