Energetics and diffusion of butene isomers in channel zeolites from molecular dynamics simulations

We have investigated the minimum energy positions and the short time self-diffusion of butene isomers in 6 zeolite structures: TON, MTT, MEL, MFI, FER, and HEU. The minimum energy positions, and the corresponding interaction energies, reflect essentially the steric interaction between the guest molecule and the host zeolite walls. It is shown that in all structures except zeolite TON, trans-2-butene diffuses faster than the other isomers, while in all cases except for TON and MTT, the diffusion of isobutene could not be followed during a 200 ps molecular dynamics run. In zeolite TON the ratio of isobutene versus linear butene self-diffusion is larger than in the other zeolites, which indicates that in this particular structure, diffusion is probably not the rate-limiting process to butene isomerization.