Tin Silsesquioxanes as Models for the “Open” Site in Tin-Containing Zeolite Beta

Abstract

The use of biomass as a resource to produce value-added products has garnered significant interest as a means of reducing reliance on fossil fuels. This task is complicated by the complex, highly functionalized nature of abundant biomass derivatives, such as glucose. Tin-containing zeolite Beta (Sn-Beta) can selectively isomerize glucose to fructose through a 1,2-intramolecular hydride shift (1,2-HS) or selectively produce mannose through a 1,2-intramolecular carbon shift (1,2-CS) by titration of the silanol groups with sodium (Na-Sn-Beta). To understand the structure–activity relationships between the conditions of the active sites in the zeolite, two molecular models (tin silsesquioxanes) of the tin sites in the zeolite were synthesized. Tin silsesquioxanes that contain an octahedral tin site with and without an adjacent silanol group selectively form fructose through a 1,2-HS and mannose through a 1,2-CS, respectively, and provide further evidence for the nature of the active sites in Sn-Beta.