A DFT study of methanol adsorption in 8T rings of chabazite

Hybrid B3LYP and gradient-corrected PW91 functionals were used for studying methanol adsorption on a zeolite cluster consisting of an 8T ring of chaba zite. The comparison of the results obtained with PW91 with periodic calcul ations has shown that the adopted ring is an adequate approximation for the Bronsted sides in chabazite. Both physisorbed and chemisorbed methanol wer e found to be a minimum on the potential energy surface, with an energy dif ference up to 10 kJ/mol in favor of the hydrogen-bonded complex. It has bee n shown that compared to B3LYP, the PW91 functional overestimates the hydro xyl bond distance and underestimates the hydrogen bond distance. In the phy sisorbed mode, the methanol oxygen atom is strongly bonded to the zeolite p roton, whereas the distance between the methanol proton and the framework o xygen atoms is 1.912-2.090 Angstrom. We have calculated for hydrogen bonded methanol hydroxyl stretch frequencies in the intervals 3677-3582 and 2358- 2187 cm(-1) for the methanol and the zeolite OH bonds, respectively.