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Influence of zeolite acidity on proton conductivity of FAU embedded imidazole.

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Title: Influence of zeolite acidity on proton conductivity of FAU embedded imidazole.
Authors: Jankowska, Aldona1 aljan@amu.edu.pl, Ostrowski, Adam2, Zieliński, Michał1, Kowalak, Stanisław1
Source: Microporous & Mesoporous Materials. Jan2019, Vol. 274, p33-42. 10p.
Subjects: Zeolites, Proton conductivity, Imidazoles, Proton transfer reactions, Hydrogen bonding, Thermal properties
Abstract: Abstract Imidazole entrapped in H-forms of FAU zeolites with various Si/Al ratios (1, 4, 40) exhibit high and stable proton conductivity (up to ∼10−3 S/cm) in a broad range of temperatures (293–393 K). The conductivity increases with temperature and imidazole loading. The number and strength of zeolite acid sites (resulting from various Si/Al) influence markedly the conductivity of composites. The samples based on zeolites with low Si/Al (1) show markedly higher conduction than these supported on the matrix with medium Si/Al (4), regardless of very similar number of the acid OH groups. The strong acid OH groups in zeolite with Si/Al = 4 result in protonation and immobilization of adsorbed imidazole, which reduce their mobility and subsequently the conduction. The low siliceous with weaker acid sites protonate imidazole and form a chain of H-bonds effective in proton propagation. Almost neutral high silica matrix provides a high mobility of dispersed imidazole, due to weak mutual interaction. The overloaded samples indicate a phase transition effect at elevated temperature due to melting of extra-matrix imidazole, which is reflected in dramatic increase in conductivity. Graphical abstract Image 1 Highlights • Proton conductivity of imidazole entrapped in H-forms of faujasites. • Role of imidazole loading, phase transition at high temperature. • Influence of Si/Al on efficiency and mechanism of conduction. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:Abstract Imidazole entrapped in H-forms of FAU zeolites with various Si/Al ratios (1, 4, 40) exhibit high and stable proton conductivity (up to ∼10−3 S/cm) in a broad range of temperatures (293–393 K). The conductivity increases with temperature and imidazole loading. The number and strength of zeolite acid sites (resulting from various Si/Al) influence markedly the conductivity of composites. The samples based on zeolites with low Si/Al (1) show markedly higher conduction than these supported on the matrix with medium Si/Al (4), regardless of very similar number of the acid OH groups. The strong acid OH groups in zeolite with Si/Al = 4 result in protonation and immobilization of adsorbed imidazole, which reduce their mobility and subsequently the conduction. The low siliceous with weaker acid sites protonate imidazole and form a chain of H-bonds effective in proton propagation. Almost neutral high silica matrix provides a high mobility of dispersed imidazole, due to weak mutual interaction. The overloaded samples indicate a phase transition effect at elevated temperature due to melting of extra-matrix imidazole, which is reflected in dramatic increase in conductivity. Graphical abstract Image 1 Highlights • Proton conductivity of imidazole entrapped in H-forms of faujasites. • Role of imidazole loading, phase transition at high temperature. • Influence of Si/Al on efficiency and mechanism of conduction. [ABSTRACT FROM AUTHOR]
ISSN:13871811
DOI:10.1016/j.micromeso.2018.07.034