Catalytic isomerization of 1-pentene to cis-2-pentene over zeolites: A quantum mechanical study

The double-bond isomerization of 1-pentene to cis-2-pentene on the surface of the molecular sieves has been investigated by using density functional theory with a cluster model simulating the zeolite materials. The microcosmic interaction of the pentene molecule with the Brønsted acid site of the zeolite leads to the formation of a π-complex, where the CC double bond is weakly coordinated to the proton of the Brønsted acid site. The transition state has an eight-member cyclic structure, in which two hydrogen atoms are situated between one oxygen atom of the zeolite and one carbon atom of the migrating double bond, respectively. The calculations of the intrinsic reaction coordinate indicate that the double-bond isomerization of 1-pentene proceeds via a concerted proton transfer between the Brønsted acid sites of the zeolite and the pentene molecules. The calculated activation energy of 11.74 kcal/mol is close to the experimental data.