Mechanistic Studies of Continuous Glucose Upgrading over Lewis Acidic Silicates by Operando UV-Vis and HSQC NMR

Lewis acidic silicates are effective catalysts for the conversion of glucose to bio-molecules of industrial interest, such as methyl lactate and methyl vinyl glycolate. Although well studied in recent years, open questions of these processes remain, particularly in regard to elements of the reaction mechanisms and how the catalysts deactivate during continuous operation. Such questions endure because of the lack of spectroscopic techniques capable of providing insights into the catalytic reaction at operational conditions. In this study, we follow the catalytic conversion of glucose over the Lewis acidic silicates Sn-Beta and Hf-Beta in a continuous flow reactor equipped with operando UV-vis spectroscopy. In doing so, we identify several transient absorption features related to the activation and conversion of glucose at various operational conditions (<150 degrees C, <25 bar). Additional spectroscopic studies (high-field (HC)-H-1-C-13 HSQC NMR) and kinetic cross-experiments allow each Sn-glucose interaction to be assigned to a particular class of product and hence to various selective or nonselective reaction pathways. Based on these assignments, operando UV-vis is used to probe how partial deactivation of the stannosilicate catalyst affects the overall performance of the glucose upgrading reaction during continuous operation. We demonstrate how deactivation during glucose conversion is nonuniform, with different reaction pathways losing activity at different rates. These findings are shown to have consequences with respect to improving the selectivity of catalysts for glucose upgrading during continuous operation.

Automated summary

This study investigates the catalytic conversion of glucose using Lewis acidic silicates in a continuous flow reactor with operando UV-vis spectroscopy. Transient absorption features related to glucose activation and conversion at various operational conditions are identified, and the deactivation of the stannosilicate catalyst is shown to affect the overall performance of the glucose upgrading reaction during continuous operation. The study highlights the nonuniform deactivation of the catalyst and its implications for improving the selectivity of catalysts for glucose upgrading.