Origin of weak Lewis acids on silanol nests in dealuminated zeolite Beta

Abstract

We report the structure of weak Lewis acid sites from silanol nests in high-silica zeolite Beta obtained by dealumination. Hydrogen bond interactions in silanol nests resulted in more electropositive hydrogens as Lewis acid sites compared with isolated silanols. The structure of the Lewis acid sites was confirmed using various characterization methods, such as NMR and IR, and DFT calculations. The amount of silanol nests, and the content and strength of the Lewis acid sites, gradually changed with the calcination temperature of high-silica zeolite Si-Beta. Double-bond migration of n-butene can be catalyzed by weak Lewis acid sites through σ species as intermediates, which was completely different from the Brønsted acid sites, as measured using in situ DRIFTS. The strengths and positions of Lewis acid sites on zeolite Si-Beta afforded reactant conversion and product selectivity in the isomerization of n-butene.