Theoretical Investigation of the Isomerization and Disproportionation of m-Xylene over Medium-Pore Zeolites with Different Framework Topologies

The strain energies of three trimethylated diphenylmethane (3mDPM) and six tetramethylated diphenylmethane (4mDPM) isomers serving as the main reaction intermediates of m-xylene isomerization and disproportionation over eight medium-pore zeolites with different framework topologies have been determined theoretically in order to elucidate the effects of zeolite pore structure on this aromatic transformation. Although the strain energies of 3mDPM and 4mDPM derivatives in MCM-22, TNU-9, and NU-87, all of which have large 12-ring cavities/channels, are always lower than 40 kJ mol(-1), some of them in cavity-free ZSM-5, ZSM-57, and TNU-10 are characterized by the strain energies higher than 40 kJ mol(-1). In particular, all the species in ZSM-22 and ZSM-23 with narrower one-dimensional 10-ring channels have the strain energies much higher than 40 kJ mol(-1). On the other hand, the energy difference (