Kinetics of the valorization of hexoses with Sn-USY catalysts in methanolic media: glycosidation vs. retroaldol cleavage†

Abstract

Catalytic performance of potassium-exchanged Sn-containing USY zeolite ([K]Sn-USY) for the transformation of hexoses into methyl lactate in methanol has been studied. This work explores the effects of temperature and catalyst loading on this transformation process, shedding light on the kinetic aspects of this process in which the starting sugars undergo a complex network of different transformations to yield different biobased products with commercial interest. The proposed kinetic model integrates several key reactions: isomerization of the starting sugars, glycosidation with the alcohol solvent, retro-aldol cleavage of carbohydrates to minor sugars, and hydrolytic side transformations. By considering these steps, insights into the determining factors that influence overall transformation and high selectivity of the [K]Sn-USY zeolite for methyl lactate are clarified. Notably, this work highlights the formation of side products, including methoxy methyl 2-hydroxy-butanoate (MMHB) and glycolaldehyde dimethyl acetal (GADMA), which have been previously overlooked in other kinetic modelling and derived from the retroaldol cleavage of aldoses. The [K]Sn-USY catalysts exhibit promising activity and selectivity, making them attractive candidates for bio-based plastic production. A comprehensive understanding of the catalytic behavior and side product formation contributes to the optimization of these catalysts for sustainable carbohydrate valorization.