Brnsted acidity of extraframework debris in steamed Y zeolites from the FTIR study of CO adsorption

Progressive CO adsorption has been studied by IR spectroscopy, at low temperature on acid-leached steamed Y zeolites and on two silica–alumina samples with different Si/Al ratios. The IR spectra of the steamed Y zeolites are complex in the ν(OH) range. After CO adsorption only some perturbed ν(OH) and ν(CO) bands had previously been assigned. This study showed that some specific Bronsted acid sites observed in steamed Y zeolites were also present in silica–alumina samples, allowing us to relate them to silica–alumina debris. On the silica–alumina samples, the more acidic site strength [characterized by a perturbed ν(OH) band near 3450 cm-1] was found to be close to that of the high-frequency (HF)OH groups of non-dealuminated HY zeolites. A quantitative estimation of such sites was obtained by determination of the molar absorption coefficient e(CO) of the corresponding perturbed ν(CO) band.