A theoretical study of the alkylation reaction of toluene with methanol catalyzed by acidic mordenite

A theoretical study of the alkylation reaction of toluene with methanol cat alyzed by the acidic Mordenite (Si/Al = 23) is reported. Cluster DFT as wel l as periodical structure DFT calculations have been performed. Full reacti on energy diagrams of the elementary reaction steps that lead to the format ion of the three xylene isomers are given. The use of periodical structure calculations allows one; to account for zeolite framework electrostatic con tributions and steric constraints that take place in zeolitic catalysts. Es pecially the steric constraint energy contribution has a significant effect on the energies and bond formation paths. The activation energy barrier of p-xylene formation is found to be similar to 20 kJ/mol lower than the corr esponding values for the formation of its isomers. Computed host-guest bind ing energies according to the DFT method need a correction due to the absen ce of the dispersive interaction with the zeolite wall. Apparent activation energies obtained with this correction are in good agreement with experime ntal data.