Abstract
The large pore zeolites containing 12-membered ring pore openings designated as Omega, Beta, ZSM- 20 and Mordenite have been investigated for their acidic properties using N1s X-ray photoelectron and FTIR spectra of chemisorbed pyridine. Deconvolution of N1s XPS spectra revealed that all zeolite samples of the present study contain relatively strong Bronsted, weak Bronsted and Lewis acid sites. The binding energy of the N1s component peak associated with strong Bronsted acid sites in Omega zeolite was found to be significantly higher than those Bronsted acid sites present in other zeolites. The results were compared with normal HY zeolite which contained only one type of Bronsted acid site and Lewis acid sites. Comparison of XPS results with IR spectroscopy data suggest that the N1s XPS method is a sensitive and reliable method to measure the strength of Bronsted acidity in zeolitic materials. Based on the N1s binding energy value zeolites are arranged for their Bronsted acid strength as follows: Omega >Beta ≥ ZSM-20 > Mordenite > HY.
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