Computational studies of water adsorption in the zeolite H-ZSM-5
- Valparaiso Univ., IN (United States)
- Argonne National Lab., IL (United States)
Ab initio molecular orbital calculations using Hartree-Fock theory and Moller-Plesset perturbation theory have been used to study the interaction of H{sub 2}O with the Broensted acid site in the zeolite H-ZSM-5. Full optimization of a 3 T atom cluster at the MP2/6-31G(d) level indicates that the `ion-pair` structure, Z{sup -}...HOH{sub 2}{sup +}, is a transition state, while the `neutral` adsorption structure, ZH...OH{sub 2}, is a local energy minimum. Partial optimization of a larger 8 T cluster at the HF/6-31G(d) level also gave results suggesting that the ion-pair structure is a transition state. Calculations were carried out to obtain corrections for high levels of theory, zero-point energies, and larger cluster size. The resulting energy difference between the neutral and ion-pair structure is small (less than 5 kcal/mol and possibly close to zero). The interaction energy of ZH...OH{sub 2} is 13-14 kcal/mol, in agreement with experiment. We find that addition of a second H{sub 2}O molecule to Z{sup -}...HOH{sub 2}{sup +} in the 3 T atom cluster stabilizes the ion-pair structure, Z{sup -}...H(OH{sub 2}){sub 2}{sup +}, making it a local energy minimum. Finally calculated vibrational frequencies for a 3 T atom cluster are used to help interpret experimental IR absorption spectra. 44 refs., 7 figs., 3 tabs.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 263160
- Journal Information:
- Journal of Physical Chemistry, Vol. 100, Issue 16; Other Information: PBD: 18 Apr 1996
- Country of Publication:
- United States
- Language:
- English
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