Adsorption of Glucose within M(IV)-Incorporated Zeolites: Insights from Periodic Density Functional Theory Calculations

Albeit the isomerization mechanism of glucose to fructose catalyzed by M(IV)-incorporated zeolites is widely studied, scant attention has been given to the adsorption of related sugars that is critical to catalysis. Here p-DFT calculations are conducted to have a comprehensive understanding within this context, considering the effects of adsorption modes, identity of framework-M(IV) ions, pore topology and conformational states of glucose. Monodentate rather than bidentate adsorption structures of glucose are the most energetically favorable within all investigated zeolites except Sn-CHA. Adsorption performances of different M(IV)-incorporated BEA zeolites decline as Zr > Sn > Ti > Ge, where Ti-and Ge-BEA, especially the latter, is obviously inferior for sugar adsorption and catalysis. Pore topology of zeolites plays an even more pronounced effect during glucose adsorption. Non-covalent interactions contribute significantly to the adsorption processes. Dispersion effects of different framework-M(IV) ions, although close to each other, show a clear opposite trend as adsorption energies. FER rather than other zeolites shows surprisingly high dispersion effects (e. g.; -218 kJ/mol for SnFER vs. -123 kJ/mol for Sn-BEA). It also shows that dispersion effects for the various conformational states of glucose are closely related with structural flexibilities.