Surface Interactions of Erythrose on Assorted Metal Oxides: A Solid-State NMR Study

Abstract

The interactions of the C4 sugar, erythrose, with various metal oxides (γ-Al2O3, CeO2, Nb2O5, SiO2, SnO2, TiO2, and ZrO2) were investigated using solid-state nuclear magnetic resonance (SS-NMR) spectroscopy. The surface species created by the impregnation of erythrose onto these oxides reveal a major shift in the equilibrium between cyclic, linear, and hydrated erythrose relative to the confirmations present in solution. Surface species on SnO2, TiO2, and ZrO2 were most significantly affected by the increase in temperature from 25 to 50 °C, while on γ-Al2O3, CeO2, Nb2O5, and SiO2, the effect was minimal. This work reports the first application of NMR relaxometry to study the interactions of erythrose with metal oxides. This was done by measuring the rotating frame relaxation time for each moiety at 25 to 50 °C revealing whether these groups interact strongly or weakly with the oxide surfaces. The Lewis and Brønsted acidity of the materials was characterized using pyridine adsorption followed by FTIR spectroscopy. Various surface reaction pathways are proposed based on the diverse array of surface species that formed. The results provide insights into the trends in surface chemistry of sugars on Lewis acidic, Brønsted acidic, redox active, and inert metal oxide surfaces.