Tighter Confinement Increases Selectivity of d‐Glucose Isomerization Toward l‐Sorbose in Titanium Zeolites

Abstract

Aqueous-phase isomerization of d-glucose to d-fructose and l-sorbose is catalyzed in parallel by Lewis acidic Ti sites in siliceous frameworks.G lucose isomerization rates (per Ti,3 73 K) are undetectable when Ti sites are confined within mesoporous voids (Ti-MCM-41, TiO 2-SiO 2) and increase to detectable values when Ti sites are confined within the smaller 12-membered ring (12-MR) micropores of Ti-Beta. Isomerization rates decrease to lower values (by % 20)with further decreases in micropore sizeasT isites are confined within 10-MR pores (Ti-MFI, Ti-CON), likely because of intrapore reactant diffusion restrictions,a nd reach undetectable values within the 8-MR pores of Ti-CHA as size exclusion prevents glucose from accessing active sites.R emarkably,t he selectivity toward l-sorbose over d-fructose increases systematically as spatial constraints around Ti sites become tighter,a nd is > 10 on Ti-MFI. These findings demonstrate the marked influence of confinement around Ti active sites on the selectivity between parallel stereoselective sugar isomerization pathways.

Removal of Sr(II) in Aqueous Solutions Using Magnetic Crayfish Shell Biochar

“…This may because, at low pH, H + competes with metal cations for the same adsorption position [68]. When the pH increased, the ability of H + to combine adsorption sites decreased, while positively charged strontium ions began to occupy adsorption sites on the surface of the adsorbent and therefore the adsorption capacity increased [69]. However, other studies showed that when the pH increased further (>9), due to the presence of a large number of anions in water, metal ions are surrounded by anions, forming negatively charged atomic groups that reduce the adsorption effect of strontium ions [70,71].…”