Promoting 5-hydroxymethylfurfural production from cellulose and wheat straw via sulfonic acid group-grafted SBA-15 mesoporous silica embedded with iron phosphate

Abstract

Efficient catalytic conversion of cellulose into 5-hydroxymethylfurfural (HMF) remains challenging and arouses concern. In this study, iron phosphate (FePO₄) was embedded into the SBA-15 mesoporous silica matrix as an available active phase via ultrasound-assisted implantation, and then the abundant silanol nests were utilized to graft sulfonic acid groups to construct an innovative FeP@SBA-15-S catalyst. Through a systematic analysis of the characteristics of crystal, texture, element valence, acidity, hydrophilicity, etc., it was reflected that FeP@SBA-15-S catalyst gave the active FePO₄ component porosity and exhibited bifunctional acidity. Without pretreatment and other acid additives, FeP@SBA-15-S catalyzed cellulose under optimal conditions provided a desired HMF yield of 52 %. More meaningfully, the cellulose and hemicellulose components in native wheat straw could be catalyzed simultaneously by FeP@SBA-15-S catalyst, yielding 61 % HMF and 60 % furfural in one-pot. The cyclability evaluation showed that the FeP@SBA-15-S catalyst still had considerable activity after six continuous runs, with a slight loss in activity attributed to the leaching of active components and pore coverage. A clear catalytic pathway was summarized by GC-MS and ¹³C NMR spectrum as cellulose undergoing glucose monomer ring opening, isomerization to fructose, fructose ring closure and final dehydration, and the by-products were also detected as mainly C₃-C₂₃ fragments and oligomers.