Synthesis of brønsted and lewis acidic solid catalyst for glucose conversion into 5-hydroxymethylfurfural

Abstract

Solid acid catalysts containing both Brønsted acidic and Lewis acidic sites were hydrothermally prepared in this work to convert glucose into 5-hydroxymethylfurfural (5-HMF). A series of catalysts was synthesized by combining metal salts (CuSO₄, ZrOCl₂, Al₂(SO₄)₃, Co (NO₃)₂) with 2,4,6-trimethylbenzene-1,3,5-trimethylphosphonic acid (H₆L) as a ligand in a hydrothermal reaction. Additionally, either 2,2-bipyridyl or 4,4-bipyridyl was added as an auxiliary ligand to adjust the internal structure and enhance the Brønsted acid strength of the catalyst, resulting in solid acid catalysts with varying Lewis acid site content. Catalyst characterization demonstrated that 4,4-bipyridine was more effective in enhancing Brønsted acid strength compared to 2,2-bipyridine. Glucose dehydration was performed to synthesize 5-HMF in a two-phase reaction solvent composed of saturated brine, sec-butanol, and methyl isobutyl ketone (1:1.6:4 ratio) at 463 K. The experiments results indicated that the CoL4 catalyst achieved a conversion yield of 89.1% and exhibited excellent thermal stability. The present study emphasizes the comparison and selection of bipotent acid solid catalysts containing different metal active sites for light use in the dehydration of glucose to 5-HMF.