Operando Solid-State NMR Observation of Solvent-Mediated Adsorption-Reaction of Carbohydrates in Zeolites

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, mani...