Sn-BEA zeolite is known to catalyze the aldose-to-ketose isomerization of xylose and glucose; however, the selectivity to pentose and hexose isomers is not stoichiometric, suggesting the formation of other products. In the present study, we have observed near-complete conversion of all pentose and hexose isomers when xylose and glucose were reacted in the presence of Sn-BEA at 140 °C and 200 °C, respectively. The previously unidentified products were identified by nuclear magnetic resonance and mass spectrometry to be hydroxyalkanoic acids and their derivatives. The hydroxyl-rich acids comprise a significant fraction of the converted sugars and are potential monomers for the synthesis of hyper-crosslinked, biodegradable polymers.

Electrochemical polarization, which often plays a critical role in driving chemical reactions at solid-liquid interfaces, can arise spontaneously through the exchange of ions and/or electrons across the interface. However, the extent to which such spontaneous polarization prevails at nonconductive interfaces remains unclear because such materials preclude measuring and controlling the degree of interfacial polarization via standard (i.e., wired) potentiometric methods. Herein, we circumvent the limitations of wired potentiometry by applying infrared and ambient pressure X-ray photoelectron spectroscopies (AP-XPS) to probe the electrochemical potential of nonconductive interfaces as a function of solution composition. As a model class of macroscopically nonconductive interfaces, we specifically probe the degree of spontaneous polarization of ZrO₂-supported Pt and Au nanoparticles immersed in aqueous solutions of varying pH. Shifts in the Pt-adsorbed CO vibrational band position evince electrochemical polarization of the Pt/ZrO₂-water interface with changing pH, and AP-XPS reveals quasi-Nernstian shifts of the electrochemical potential of Pt and Au with pH in the presence of H₂. These results indicate that spontaneous proton transfer via equilibrated H⁺/H₂ interconversion spontaneously polarizes metal nanoparticles even when supported on a nonconductive host. Consequently, these findings indicate that solution composition (i.e., pH) can be an effective handle for tuning interfacial electrical polarization and potential at nonconductive interfaces.

[This retracts the article DOI: 10.1021/jacsau.2c00402.].