The study of active sites for producing furfural and soluble oligomers in fructose conversion over HZSM-5 zeolites

Furfural, generally achieved from hemicelluloses and its derived pentose, is a high value-added product. The formation of furfural from cellulose and hexose remains challenging. The acid sites in zeolites are the major active sites for preparing furfural from hexose. The catalytic performance of zeolites can be improved by increasing the number of active sites for the preparation of furfural. In this work, HZ-Na free-m and HZ-Na-m zeolites were prepared through without or with adding Na + ions in the mother gels, respectively. GHB (hydrolysate of GBL) was the active site for the formation of acyclic fructose precursor (Intermediate 2). Acyclic fructose production and the following dehydration for producing furfural were favored by the middle strong and strong Brønsted acids in the channels of HZSM-5. Meanwhile, middle strong and strong Brønsted acids were favored the production of HMF from fructose and furfural from xylose. The exterior weak Lewis acid of HZSM-5 could promote the formation of soluble oligomers. The soluble oligomers were composed by HMF and furfural through condensation, etherification, nucleophilic attack and electrophilic attack. HMF molecule was easy to participate in the production of soluble oligomers than furfural molecule over exterior weak Lewis acid of HZSM-5.