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The Bronsted acidity of three- and two-dimensional zeolites
Authors: Thang Ho Viet | Vaculík Jan | Prech Jan | Kubu Martin | Cejka Jiri | Nachtigall Petr | Bulánek Roman | Grajciar Lukas
Year: 2019
Type of publication: článek v odborném periodiku
Name of source: Microporous and Mesoporous Materials
Publisher name: Elsevier Science BV
Place: Amsterdam
Page from-to: 121-132
Titles:
Language Name Abstract Keywords
cze Bronstedova kyselost tří- a dvou-dimenzionálních zeolitů Aktivita zeolitů v procesech řízených Bronstedovými kyselými centry je stanovena pomocí distribuce protonů v zeolitu a síly jejich interakce s mřížkou. Tato studie je zaměřena na míru v jaké transformace 3D zeolitů na odpovídající 2D zeolity mění jejich protonovou distribuci a sílu interakce protonů s mřížkou. Bronstedova kyselost; zeolit; adsorpce; FTIR; DFT
eng The Bronsted acidity of three- and two-dimensional zeolites The zeolite activity in processes driven by Bronsted acid sites is determined by the distribution of the protons in the zeolite and strength of their interaction with the framework. This study aims to assess how much the transformation from three-dimensional (3D) bulk zeolite to its corresponding two-dimensional (2D) layered form changes the proton distribution and strength of the proton-framework interaction and thus how much it affects the zeolite Bronsted acid strength. Zeolites with three distinct topologies, MWW, PCR, and MFI, which form also layered analogues with considerably different thickness and silanol density were considered. To probe the Bronsted acidity of both 3D and 2D forms, an array of typical acidity descriptors (i.e., O-H stretching frequency, shift of O-H frequencies upon adsorption of CO probe molecule, C-O stretching frequencies and adsorption enthalpies of the CO adsorption complex) have been evaluated, employing both dispersion-corrected density functional theory and Fourier-transform infrared spectroscopy. Using these descriptors, the Bronsted acidity of 2D form is, on average, the same or just slightly lower than that of the 3D form. Transformation to layered form does affect the proton distribution and values of acidity descriptors for individual T sites, however, if all T sites are considered, the aggregate effect is almost negligible. Hence, these results suggest that a larger effect of the 3D - > 2D transformation can be expected for frameworks with fewer distinct T sites. Bronsted acidity; zeolite; OH stretching frequency; CO stretching frequency; Adsorption; Fourier-transform infrared spectroscopy; Density functional theory

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