ESTIMATION OF POTENTIAL AND EFFECTIVE BRONSTED ACID SITE CONCENTRATIONS IN ACIDIC MORDENITES BY CONDUCTOMETRIC TITRATION METHOD

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ZANJANCHI M.A.; MOHAMMADI M.

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ISSN: 2588-4824

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Journal: Journal of Sciences, Islamic Republic of Iran Year:2001 | Volume:12 | Issue:2 Page(s): 133-139

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Title

ESTIMATION OF POTENTIAL AND EFFECTIVE BRONSTED ACID SITE CONCENTRATIONS IN ACIDIC MORDENITES BY CONDUCTOMETRIC TITRATION METHOD

Author(s)

ZANJANCHI M.A. | MOHAMMADI M. | Issue Writer Certificate

Keywords

CONDUCTOMETRIC TITRATION; AMMONIUM MORDENITE; BRONSTED ACID SITES; ACIDIC MORDENITE; EXTRA-FRAMEWORK ALUMINUM; DIFFUSE REFLECTANCE SPECTROSCOPY

Abstract

Quantitative determination of Bronsted acid sites in acidic mordenite samples with varying proton concentrations has been studied using aqueous conductometric titration method. Conductometric titration of the ammonium form of mordenite with sodium hydroxide is feasible and the results indicate potential number of Bronsted acid sites. However, Bronsted acid sites concentration in acidic mordenites, measured by this method, is less than that evaluated by ammonium-mordenite titration. Calcination procedure, to produce acidic mordenites from its ammonium form, reduces Bronsted acid sites by dealumination and dehydroxylation processes. In conductometric titration, only accessible Bronsted acid sites are titrated and extra-framework aluminum species, which are generated during calcination and reside in the structure, are not titrated. This finding is supported by observing more reduction in the Bronsted acidity when higher temperatures of calcination are employed. Also, comparing diffuse reflectance spectra of the acidic mordenite before and after titration does not show extra-framework aluminum species reacting with added base. A negative linear correlation was observed between concentration of Bronsted acid sites measured by conductometric titration and the temperature of calcination within 450-750°C.

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