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

• Published in: Journal of catalysis Vol. 380; pp. 204 - 214
• Main Authors: Yi, Fengjiao, Chen, Yunlei, Tao, Zhichao, Hu, Caixia, Yi, Xianfeng, Zheng, Anmin, Wen, Xiaodong, Yun, Yifeng, Yang, Yong, Li, Yongwang
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.12.2019
• Subjects: Hydrogen bonds; Lewis acids; N-butene isomerization; Si-Beta; Silanol nests; Silanol nests; Lewis acids; Hydrogen bonds; Si-Beta; N-butene isomerization
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2019.10.008

Structure of weak Lewis acid sites from silanol nests in high-silica zeolite Beta was obtained by dealumination. Hydrogen bond interactions in silanol nests resulted in more electropositive hydrogens as Lewis acid sites compared with isolated silanols. Hydrogens in silanol nests would interact with probe molecule TMP directly, with electrons induced to adjacent oxygen and silicon, leading to silanol nests conducting a Lewis acid mechanism during reactions. [Display omitted] •Weak Lewis acids were from silanol nests in completely dealuminated zeolite.•Origin of weak Lewis acids was clear by characterizations and DFT calculation.•The acidic properties of Lewis acids gradually changed with calcination temperatures.•Mechanism of Lewis acids was different from that of Brønsted acids.•Lewis acid strength afforded catalytic performance in the isomerization of n-butene. 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.