Synthesis and characterization of functionalized alumina catalysts with thiol and sulfonic groups and their performance in producing 5-hydroxymethylfurfural from fructose

Abstract

5-Hydroxymethylfurfural (HMF) has been identified as a potential candidate for biofuels and a high-potential intermediate chemical compound. The obtention of HMF from fructose is efficiently carried out using acid catalysts. In this work, a new catalyst of alumina synthesized by sol-gel as support was bifunctionalized with thiol (SH) and sulfonic (SO3−) groups by the grafting method and compared with other supports, i.e., synthesized boehmite and commercial alumina. The 3-mercaptopropyl-trimethoxysilane was utilized as a source of the thiol group to promote fructose tautomerization to its furanose form. The sulfonic group was obtained from 1,3-propanesultone, which carries out the dehydration of the fructose molecule. The prepared bifunctionalized catalysts were tested in the fructose dehydration reaction. The functional groups were identified through Fourier transform infrared spectroscopy (FTIR) as the primary characterization. The type of acid site was identified by Fourier transform infrared spectroscopy (–pyridine (FTIR-py)) and quantified by temperature-programmed desorption of ammonia (TPD-NH3). The molecular structures of thiol and the sulfonic groups anchored on the supports were resolved by nuclear magnetic resonance with cross-polarization (CP) and magic angle spinning (MAS) (CP-MAS-NMR). The bifunctionalized catalyst of alumina synthesized by sol-gel, being a very competitive material, reached a 55% selectivity to HMF at a 72% conversion at 453K.