OSDA-Free Zeolite Beta with High Aluminum Content Efficiently Catalyzes a Tandem Reaction for Conversion of Glucose to 5-Hydroxymethylfurfural

Abstract

Organic structure-directing agent (OSDA)-free zeolite Beta with high Al content exhibit remarkably high catalytic performance in the conversion of glucose to 5-hydroxymethylfurfural (HMF) by virtue of their appropriate acid properties; specifically, a sufficient number of Lewis acid sites were generated by calcination of the NH4-form zeolite, while the original Brønsted acid sites were substantially maintained, with both acid sites being in close proximity. The OSDA-free Beta catalyst, having a large number of Brønsted acid sites and sufficient Lewis acid sites, showed superior catalytic performance to a physical mixture of each type of acid catalyst with a similar number of each acid site. This behavior could be ascribed to the high reactivity and slow intrazeolitic diffusion of fructose. The structure of the Al species active in the isomerization of glucose to fructose is discussed based on relationships between catalytic activities and changes in Al species by the calcination, changes that were observed by 27Al magic-angle spinning (MAS) NMR and IR spectroscopies. Lewis and Brønsted, working together: Organic structure-directing agent (OSDA)-free zeolite Beta with high Al content effectively promotes conversion of glucose to 5-hydroxymethylfurfural (HMF). The high aluminum content of the zeolite provides suitable acid properties; specifically, a large number of Brønsted acid sites with a sufficient number of Lewis acid sites in close proximity. The zeolite calcined at 773 K showed >70 % yield of HMF.