Molecular traffic control for catalytic oxidation reaction in TS-1 zeolite

For four decades, the definition of “molecular traffic control (MTC effect)” in zeolite shape selective catalysis has been controversially discussed. So far, there is no clear evidence to prove the existence of MTC effect in the catalytic oxidation reaction. In this work, a series of TS-1 zeolites with homogeneous distribution of Ti atoms and free of extra-framework Ti species and/or anatase were synthesized, they were used to catalyze the oxidation of 1-hexene, 4-methyl-1-pentene and styrene. The systematic investigations exhibited that the catalytic oxidation process of TS-1/H₂O₂ occurred in both straight and sinusoidal channels when 1-hexene was used as substrate. When 4-methyl-1-pentene and styrene were used as substrates, the catalytic oxidation process of TS-1/H₂O₂ tended to occur in the straight channel, and the larger the size of the substrate, the more the oxidation reaction tends to occur in the straight channel. The above characteristics of oxidation performance are consistent with the intracrystalline diffusion characteristics of substrate molecules proposed by Derouane's group. It provides an evidence that MTC effect exists in TS-1/H₂O₂ catalytic oxidation reaction. The proof of MTC effect is of great significance to the development of the mechanism of heterogeneous reaction process.