The use of polar aprotic solvents in acid-catalyzed biomass conversion reactions can lead to improved reaction rates and selectivities. We show that further increases in catalyst performance in polar aprotic solvents can be achieved through the addition of inorganic salts, specifically chlorides. Reaction kinetics studies of the Brønsted acid-catalyzed dehydration of fructose to hydroxymethylfurfural (HMF) show that the use of catalytic concentrations of chloride salts leads to a 10-fold increase in reactivity. Furthermore, increased HMF yields can be achieved using polar aprotic solvents mixed with chlorides. Ab initio molecular dynamics simulations (AIMD) show that highly localized negative charge on Cl − allows the chloride anion to more readily approach and stabilize the oxocarbenium ion that forms and the deprotonation transition state. High concentrations of polar aprotic solvents form local hydrophilic environments near the reactive hydroxyl group which stabilize both the proton and chloride anions and promote the dehydration of fructose.

In the liquid-phase catalytic processing of molecules using heterogeneous catalystsan important strategy for obtaining renewable chemicals from biomassmany of the key reactions occur at solid–liquid interfaces. In particular, glucose isomerization occurs when glucose is adsorbed in the micropores of a zeolite catalyst. Since solvent molecules are coadsorbed, the catalytic activity depends strongly and often nonmonotonically on the solvent composition. For glucose isomerization catalyzed by NaX and NaY zeolites, there is an initial steep decline when water is mixed with a small amount of the organic cosolvent γ-valerolactone (GVL), followed by a recovery as the GVL content in the mixed solvent increases. Here we elucidate the origin of this complex solvent effect using operando solid-state NMR spectroscopy. The glucopyranose tautomers immobilized in the zeolite pores were observed and their transformations into fructose and mannose followed in real time. The microheterogeneity of the solvent system, manifested by a nonmonotonic trend in the mixing enthalpy, influences the mobility and adsorption behavior of the carbohydrates, water, and GVL, which were studied using pulsed-field gradient (PFG) NMR diffusivity measurements. At low GVL concentrations, glucose is depleted in the zeolite pores relative to the solution phase, and changes in the local structure of coadsorbed water serve to further suppress the isomerization rate. At higher GVL concentrations, this lower intrinsic reactivity is largely compensated by strong glucose partitioning into the pores, resulting in dramatic (up to 32×) enhancements in the local sugar concentration at the solid–liquid interface.

Interactions between organic molecules and inorganic materials are ubiquitous in many applications and often play significant roles in directing pathways of crystallization. It is frequently debated whether kinetics or thermodynamics...

In catalytic applications of surface-modified mesoporous silica materials, distinguishing and quantifying different types of functional groups on the surface is crucial for enabling accurate evaluation of catalytic activity and possible cooperativity among mixed functional groups.