FTIR study of N2 and CO adsorption on H-D-FER

•Three kinds of bridging hydroxyls are detected on H-FER.•Adsorption of N2 at 100 K allows selective measuring of the acidity of the OH groups.•CO is not appropriate IR probe for measuring acidity of FER bridging hydroxyls.

Low temperature adsorption of N2 on an H-D-FER sample was studied by FTIR spectroscopy in order to obtain information on the acidity of the hydroxyl groups. Three kinds of zeolite bridging hydroxyls were clearly distinguished, at 3609, 3596 and 3555 cm−1 (3614, 3600 and 3556 cm−1 at 100 K). The respective OD groups were observed at 2662, 2653 and 2623 cm−1 (2666, 2656 and 2621 cm−1 at 100 K). Nitrogen affects first the highest-frequency hydroxyls and last, the lowest frequency ones. A shift of the OH modes between 90 and 111 cm−1 was measured for the different hydroxyls (between 64 and 79 cm−1 for the OD groups). Experiments on CO adsorption have shown that this molecule was not convenient for measuring the acidity of the bridging hydroxyls because the spectra are complicated as a result of Fermi resonance and solvatation effects.

Graphical abstractLow temperature adsorption of N2 on H-D-FER clearly reveals the heterogeneity of the bridging hydroxyls.Figure optionsDownload full-size imageDownload as PowerPoint slide