CO adsorption on superacid sites on dealuminated mazzite

Autor: B. Chiche, R.A. Shigeishi, François Fajula
Rok vydání: 2001
Předmět:
Zdroj: Microporous and Mesoporous Materials. 43:211-226
ISSN: 1387-1811
DOI: 10.1016/s1387-1811(00)00365-6
Popis: Spectra of CO adsorption on dealuminated mazzite activated at temperatures in excess of 400°C have revealed two Bronsted acid sites with OH peak positions at 3626 and 3606 cm −1 and corresponding CO peaks at 2180 and 2165 cm −1 . These Bronsted sites are located in the large and small channels of mazzite. Strong Lewis sites have been detected at low CO coverages at 2229 and 2188 cm −1 . For the first time, evidence is presented for the direct interaction of these Bronsted and Lewis sites. When Lewis sites are bare they interact with Bronsted sites and shift the OH peaks to 3590 and 3567 cm −1 . These are superacid OH sites located in the two types of channels in mazzite. When the Lewis sites are filled with CO their interaction with the Bronsted sites is attenuated and the OH peaks revert to their values at 3626 and 3606 cm −1 . CO adsorption on these Bronsted sites shifts the OH peaks to 3247 ( Δν =379 cm −1 ) and 3330 cm −1 ( Δν =276 cm −1 ) respectively. The high frequency OH site at 3626 cm −1 is the strongest acid site detected on mazzite. At high CO pressures a weaker Al–OH acid site detected at 3660 cm −1 is shifted to 3450 cm −1 ( Δν =210 cm −1 ) at the same time that a CO peak appears at 2160 cm −1 . The conversion rate for the isomerization of n -butane on mazzite is much higher than that on H-ZSM5 and consistent with very strong acid sites.
Databáze: OpenAIRE
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