(735i) Quantification of Bronsted and Lewis Acid Sites on Zeolites in the Presence of Solvents
Many biomass derived feedstocks are highly oxygenated, meaning reactions cannot be conducted in gas phase without risking significant decomposition. However, the liquid phase incurs additional interactions and thermodynamic considerations which are not well understood. Fundamental understanding of solvent effects, including how solvent choice affects catalyst structure, catalyst acidity, and product distributions is still lacking. To provide experimental insight, attenuated total reflection (ATR) Fourier transform infrared spectroscopy (FTIR) was used to study the in-situ interactions between solvent, substrate, and catalyst. Specifically, pyridine was used as a probe molecule to characterize the relative ease of protonation by proton exchanged zeolites in solution. This has been used to understand how solvent choice affects substrate protonation, zeolite acidity, and activity in Brønsted acid catalyzed reactions. However, the FTIR technique is limited by its inability to quantify adsorbed and bulk species without integrated molar extinction coefficients (IMEC), or the amount of signal per mole of adsorbed or bulk species. A method has been established for vapor phase IMECs, but liquid phase IMECs are still missing. We develop a simple method to obtain IMECs of pyridine adsorbed on zeolites in the liquid phase in an ATR cell. Densities of Bronsted and Lewis acid sites on H/Y, H/Beta, and H/ZSM-5 of varying Si/Al ratios in solvents water, acetonitrile, and ethanol have been quantified with this method.