Thesis (M.Sc.)--Chulalongkorn University, 2007

Reaction mechanisms of methanol and ethanol conversion to dimethyl ether, diethyl ether and ethylene on the H-ZSM-5 were investigated using a 56/5T cluster model of H-ZSM-5 in corporation with the two-layered ONIOM(B3LYP/6-31G(d):AM1) approach. The concerted and stepwise mechanisms of methanol and ethanol conversion to dimethyl ether, diethyl ether and ethylene were comparatively studied. The concerted process occurring over Bronsted acid site of H-ZSM-5 zeolite is more favorable by 11.37 kcal/mol than the stepwise process in methanol coversion to dimethyl ether and 20.15 kcal/mol than the stepwise reaction in ethanol conversion to diethyl ether. In the stepwise reaction of ethanol conversion to ethylene occurring over Bronsted acid site of H-ZSM-5 zeolite is moer favorable by 9.11 kcal/mol than the conserted reaction. In the concerted reaction of ethanol conversion to diethyl ether occurring over Bronsted acid site of H-ZSM-5 zeolite is more favorable by 29.26 kcal/mol than the concerted process in ethanol conversion to ethylene. In the stepwise reaction of ethanol conversion to ethylene occurring over Bronsted acid site of H-ZSM-5 zeolite is more favorable by 28.07 kcal/mol than the stepwise process in ethanol conversion to diethyl ether. These reaction mechanisms in acid-catalyzed system were also investigated and compared to their corresponding reactions. The reaction energies and thermodynamic properties of all reaction mechanisms are reported.