ZIF-8 Metal Organic Framework for the Conversion of Glucose to Fructose and 5-Hydroxymethyl Furfural

• Main Authors: Ryan Oozeerally, Shivendra D. K. Ramkhelawan, David L. Burnett, Christiaan H. L. Tempelman, Volkan Degirmenci
• Format: Article
• Language: English
• Published: MDPI AG 2019-09-01
• Series: Catalysts
• Subjects: metal organic framework; zeolitic imidazolate framework; hmf; biomass; catalysis; glucose
• Online Access: https://www.mdpi.com/2073-4344/9/10/812

Herein, Zeolitic imidazolate framework-8 (ZIF-8) is considered as an easy and cheap to prepare alternative catalyst for the isomerization of glucose and production of 5-hydroxymethyl furfural (HMF). For the synthesis of the ZIF-8 catalysts two preparation methods were evaluated, being room temperature and hydrothermal synthesis at 140 °C. Of these, the hydrothermal synthesis method yields a material with exceptionally high surface area (1967 m²·g^−1). As a catalyst, the ZIF-8 materials generated excellent fructose yields. Specifically, ZIF-8 prepared by hydrothermal synthesis yielded a fructose selectivity of 65% with a glucose conversion of 24% at 100 °C in aqueous reaction medium. However, this selectivity dropped dramatically when the reactions were repeated at higher temperatures (~140 °C). Interestingly, greater quantities of mannose were produced at higher temperatures too. The lack of strong Brønsted acidity in both ZIF-8 materials resulted in poor HMF yields. In order to improve HMF yields, reactions were performed at a lower pH of 1.0. At 140 °C the lower pH was found to drive the reaction towards HMF and double its yield. Despite the excellent performance of ZIF-8 catalysts in batch reactions, their activity did not translate well to the flow reactor over a continuous run of 8 h, which was operating with a residence time of 6 min. The activity of ZIF-8 halved in the flow reactor at 100 °C in ~3 h, which implies that the catalyst’s stability was not maintained in the long run.