Modification of commercial Y zeolites by alkaline-treatment for improved performance in the isomerization of glucose to fructose

Abstract

Isomerization of glucose to fructose is a key reaction step in the efficient production of valuable renewable chemical intermediates from biomass. Zeolites have been widely used to promote glucose isomerization, but only limited structure-activity relationship has been established and applied to optimize the reaction. In this work, commercial Y zeolites were modified by alkaline-treatment and their physicochemical properties and structures were correlated in order to optimize the catalytic performance for glucose isomerization. For H-Y, the alkaline-treatment developed new mesoporous structures with larger pore, modified the Si-O(H)-Al bonds and extracted silica from framework structures creating more tetrahedral extra-framework Lewis acidic aluminum. This increased the isomerization selectivity towards fructose more than twelve times and decreased significantly acetalization/ketalization side reactions compared to the pristine zeolite. In contrast, Na-Y contained mainly micropores and had less tetrahedral non-framework acidic Al-species, resulting in low glucose conversion and low fructose yield due to limited substrate accessibility to the pores, although the number of acid sites was tenfold higher than in H-Y. The study demonstrates how commercial Y zeolites can be designed by alkaline-treatment to comprise mesopores and weak acid sites, which greatly improve the catalytic performance for glucose isomerization to fructose.