Theoretical Modeling of Pathways of Transformation of Fructose and Xylose to Levulinic and Formic Acids over Single Na Site in BEA Zeolite

The aim of our work is to theoretically model the conversion of C6 and C5 carbohydrates derived from lignocellulosic biomass waste into C1–C5 carboxylic acids such as levulinic, oxalic, lactic, and formic acids. Understanding the mechanism of these processes will provide the necessary knowledge to better plan the structure of zeolite. In this article, we focus on the theoretical modeling of two carbohydrates, representing C5 and C6, namely xylose and fructose, into levulinic acid (LE) and formic acid (FA). The modeling was carried out with the participation of Na-BEA zeolite in a hierarchical form, due to the large size of the carbohydrates. The density functional theory (DFT) method (StoBe program) was used, employing non-local generalized gradient-corrected functions according to Perdew, Burke, and Ernzerhof (RPBE) to account for electron exchange and correlation and using the nudged elastic band (NEB) method to determine the structure and energy of the transition state. The modeling was performed using cluster representations of hierarchical Na-Al2Si12O39H23 and ideal Al2Si22O64H34 beta zeolite. However, to accommodate the size of the carbohydrate molecules in reaction paths, only hierarchical Na-Al2Si12O39H23 was used. Sodium ions were positioned above the aluminum centers within the zeolite framework.