Propyl sulfonic acid functionalization of faujasite-type zeolites: Effect on water and methanol sorption and on proton conductivity

In this work the functionalization of three commercial faujasites with different chemical composition and textural properties was carried out by post-grafting of mercapto-propyl groups followed by conversion into propyl sulfonic acid groups. The first part of the work was centered on the study of the effect of the chemical and textural properties of the zeolites on the silane grafting yield, revealing a higher extent of functionalization for samples with higher content of Al. Then, the effect of the grafting on textural and sorption properties of the faujasites, and the interplay between these properties and the proton conductivity was studied. In spite of the significant reduction of porosity and water sorption, functionalized zeolites showed increased proton conductivity, up to one order of magnitude. Moreover, water to methanol selectivity vapor improved with the degree of functionalization.

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► A higher amount of organosilane is grafted onto zeolites with higher Al content.
► The zeolites’ proton conductivity is 10 times higher after functionalization with –SO3H.
► For an equal amount of –SO3H, the proton conductivity increases with water uptake.
► The silane grafting improves the water to methanol vapor selectivity at high P/P0.