Abstract
The oxidation mechanisms of thiophene (Tp) with H2O2 over defect and perfect titanium silicalite-1 (TS-1) were investigated by means of DFT/ONIOM2 calculations for different models 7T:45T, 9T:45T and 13T:45T. The B3LYP, ωB97X-D, and M06-2X functionals were used in the high-level part of ONIOM2, with PM6 in the lower-level part. The related potential energy surface profiles are constructed based on the ωB97X-D/ONIOM2 method for 13T:45T cluster. Four possible paths are proposed for the oxidation of Tp into sulfoxide and sulfoxide into sulfone using H2O2 as an oxidant over defect and perfect TS-1. The dimerization of sulfoxide and sulfone through Diels–Alder cycloaddition is also studied. It is found that perfect TS-1 is highly unfavorable compared to defect TS-1 (TS-d). The calculated activation energy of Tp oxidation with TS-d is found to be remarkably lower than that without any zeolite catalyst. The calculated results may contribute to the understanding of the reaction mechanism of the catalytic oxidative desulfurization of sulfides in liquid fuels.
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