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Pore Selectivity for Olefin Protonation Reactions Confined inside Mordenite Zeolite

Release time:2013-1-18      Source:admin      Reads:1384

                Yueying Chu, Bing Han, Anmin Zheng *, Xianfeng Yi, and Feng Deng *

    The activity of olefins protonated by Brønsted acid sties in different pore structures (12-MR and 8-MR channel) of mordenite (MOR) zeolite is investigated by the B3LYP+D/6-31G(D,P)//ONIOM(B3LYP/6-31G(D,P):MNDO) method to reveal the pore selectivity for the protonation reaction. It is demonstrated that for ethene, the size of the molecule is smaller compared with the zeolite pores (both 12-MR and 8-MR channels), the pore confinement effect is weak, and the intrinsic acid strength of the solid acid plays a key role in the reaction, resulting in that the ethene protonation occurs preferentially at the strong acid sites within the 12-MR channel. For propene, the reaction can occur inside both channels (12-MR and 8-MR) due to the reactant being well fitted into the 8-MR channel of MOR zeolite. In this case, the confinement effect that stabilizes the intermediates and transition states compensates the deficiency of acid sites in the 8-MR channel. However, for the bulky isobutene, the protonation reaction occurs selectively in the 12-MR channel as the size of the reactant is larger than the size of the 8-MR channel, which results in a pronounced destabilizing effect due to the steric constraint.