Effects of the acidity and shape selectivity of dealuminated zeolite beta on butene transformations

Abstract

The acidity and shape selectivity of zeolites are two important catalytic properties, and they have been extensively applied to the chemical and petrochemical industries. Here, we investigated the various effect mechanisms of Brønsted acid sites (BASs) from bridged hydroxyl groups in zeolite Beta and Lewis acid sites (LASs) from silanol nests in Si-Beta on butene transformation and their reaction pathways by diffuse-reflectance infrared Fourier-transform spectroscopy. BAS catalysis of butenes double bond activation and isomerization follows the classical carbenium ion mechanism, while catalysis by silanol nests as weak LASs due to hydrogen bond interaction is achieved by formation of allyl species and alkoxyl groups. Moreover, the oligomerization reactions of butene isomers are affected by the dynamic diameters and activation energies of the butene isomers and the synergy between acidity and shape selectivity of the zeolite. Oligomerization of n-butene and cis-2-butene is more likely to be affected by acids on the sample, while oligomerization of trans-2-butene and isobutene is influenced by the shape selectivity of the channel, in addition to the acidity on partly dealuminated zeolite Beta.