Adsorption of methanol on the nanocrystalline H-zeolite and alkali metal exchanged M-zeolites: Energetic, NBO and QTAIM analyses

Adsorption of methanol on the H-zeolitc and ion-exchanged M-zeolites (M = Li, Na, and K) has been investigated using 3T cluster model at the B3LYP/6-31++G(d,p) and MP2/6-31++G(d,p) levels and 5T cluster model at 133LYP/6-31++G(d,p) level of theory. The I adsorption energy of methanol on the M-zeolites (M = Li, Na, and K) decreases when the cations (M+) are changed from Li+ to K+, in agreement with the weaker acidity of K+ ion compared to the Li+ ion. The proton jump between neighboring oxygen atoms of Al center has been studied in five cluster models. The electron density (rho), Laplacian of electron density (del(2)rho) and energy density (H) estimated by AIM calculations, showed that both H-M center dot center dot center dot O-Z and O-M center dot center dot center dot H-Z hydrogen bonds are partially covalent and partially electrostatic in nature, whereas both O-Z-H-Z and O-M-H-M have covalent character. del(2)rho and H(r) values at M center dot center dot center dot O-M (M = Li, Na, and K) BCP of complexes are positive and decrease on going from complex Li+ to complex K+. As a result, electrostatic nature of M center dot center dot center dot O-M interaction decreases on going from complex Li+ to complex K+. Also, the interaction between methanol and the ZSM-5 zeolites has been examined using the natural bond orbital (NBO) analysis. (C) 2007 Elsevier Inc. All rights reserved.