High-electrophilic (SiO)2Nb(OH)(=O) sites confined in silanol defects over Nb-Beta zeolite for efficient cyclic alkene epoxidation reactions

Yan Chen; Guojun Lv; Xuyang Zou; Shihao Su; Jiangzhang Wang; Chaoyi Zhou; Jialing Shen; Yangbin Shen; Zhongmin Liu

doi:10.1016/j.jcis.2024.03.076

High-electrophilic (SiO)₂Nb(OH)(=O) sites confined in silanol defects over Nb-Beta zeolite for efficient cyclic alkene epoxidation reactions

J Colloid Interface Sci. 2024 Jun 15:664:626-639. doi: 10.1016/j.jcis.2024.03.076. Epub 2024 Mar 12.

Authors

Yan Chen¹, Guojun Lv², Xuyang Zou¹, Shihao Su¹, Jiangzhang Wang¹, Chaoyi Zhou¹, Jialing Shen¹, Yangbin Shen³, Zhongmin Liu⁴

Affiliations

¹ School of Environmental and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, PR China.
² School of Environmental and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, PR China. Electronic address: jkdlgj@just.edu.cn.
³ Institute of Materials Science and Devices, Suzhou University of Science and Technology, Suzhou, 215009, PR China.
⁴ School of Chemistry and Chemical Engineering, Dezhou University, Dezhou 253023, PR China.

PMID: 38490038
DOI: 10.1016/j.jcis.2024.03.076

Abstract

Dealuminated Beta zeolite has a large amount of silanol defects on its interface, which provides an ideal place for embedding metal species and creating metal active sites in a confined microenvironment. The confined metal sites as well as their surroundings are closely related to the reactant activation and transient state achievement. Hence, unraveling the confined metal sites is of great significance for the catalytic reaction process. Herein, niobium species were incorporated into the silanol defects over dealuminated Beta zeolite with a facile dry impregnation method, co-grinding the niobium precursor with dealuminated Beta zeolite support. The successful incorporation of niobium into the silanol defects for 30Nb-Beta zeolite was verified by DRIFT, ¹H MAS NMR, UV-Vis and UV-Raman characterizations. XAS characterization and DFT calculations further disclosed that the confined Nb species existed as (SiO)₂Nb(OH)(=O), containing two Si-O-Nb bonds, one Nb=O bond as well as one Nb-OH bond. The synthesized 30Nb-Beta zeolite catalyst displayed a superior cyclohexene conversion of 51.1%, cyclohexene oxide selectivity of 83.1% as well as TOF value of 188.2 h^-1 ascribed to the inherent electrophilicity of Nb(V) for confined (SiO)₂Nb(OH)(=O) species as well as the low oxygen transfer energy barrier for Nb^V-OOH species. Furthermore, the prepared 30Nb-Beta zeolite can be effectively employed to other cyclic alkene epoxidation reactions.

Keywords: (SiO)(2)Nb(OH)(=O) species; Cyclohexene epoxidation; Dealuminated Beta zeolite; Nb-Beta zeolite; Silanol defect.