Insights into Sorption and Molecular Transport of Aqueous Glucose into Zeolite Nanopores

Liquid-phase heterogeneous catalysis using zeolites is important for biomass conversion to fuels and chemicals. There is a substantial body of work on gas-phase sorption in zeolites with different topologies; however, studies investigating the diffusion of complex molecules in liquid medium into zeolitic nanopores are scarce. Here, we present a molecular dynamics study to understand the sorption and diffusion of aqueous beta-D-glucose into beta-zeolite silicate at T = 395 K and P = 1 bar. Through 2-mu s-long molecular dynamics trajectories, we reveal the role of the solvent, the kinetics of the pore filling, and the effect of the water model on these properties. We find that the glucose and water loading is a function of the initial glucose concentration. Although the glucose concentration increases monotonically with the initial glucose concentration, the water loading exhibits a nonmonotonic behavior. At the highest initial concentration (similar to 20 wt %), we find that the equilibrium loading of glucose is approximately five molecules per unit cell and displays a weak dependence on the water model. Glucose molecules follow a single-file diffusion in the nanopores due to confinement. The dynamics of glucose and water molecules slows significantly at the interface. The average residence time for glucose molecules is an order of magnitude larger than that in the bulk solution, while it is about twice as large for the water molecules. Our simulations reveal critical molecular details of the glucose molecule's local environment inside the zeolite pore relevant to catalytic conversion of biomass to valuable chemicals.

Automated summary

Liquid-phase heterogeneous catalysis using zeolites is crucial for converting biomass into fuels and chemicals. This study investigates the sorption and diffusion of aqueous beta-D-glucose into beta-zeolite silicate, revealing the role of solvent, kinetics of pore filling, and water model on these properties. The results show that glucose molecules undergo single-file diffusion in the nanopores, while the dynamics of glucose and water molecules slow at the interface. The study provides critical molecular details for catalytic biomass conversion.