Clay supported earth-abundant metal phosphide nanoparticles catalyzing sugar conversion to value-added chemicals

Abstract

Sugar conversion can produce high value-added chemicals such as HMF, levulinic acid, formic acid and other derivatives. Successful sugar conversion was witnessed using both heterogeneous and homogeneous catalysts, giving mostly one-step converted products. This work aims to transform monosaccharides (i.e., glucose and fructose) to HMF and HMF-reduced products such as BHMF through a one-pot tandem catalysis. Therefore, an acid-catalyzed Cr-exchanged montmorillonite K10 clay (Cr-K10) and a hydrogenate metal phosphide nanoparticles (NixCo₂-xP) were combined. Metal phosphide nanoparticles were thermally synthesized using Ni(II) and/or Co(II) salt with phosphite salt, in the presence of surfactants. The NPs were later dispersed on to the surface of Cr-K10. The synthesized catalysts were characterized by several spectroscopic techniques to confirm the chemical structure. In addition, effects of different types of ionic liquids including N-methylimidazolium chloride ([HMIM]Cl), 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) and N-methylimidazolium bisulfate ([HMIM][HSO₄]) on the catalytic activity were investigated. Due to the time limit, the catalytic performance towards conversion of sugar into HMF was only examined. Results demonstrated that using [HMIM]Cl as medium provided the highest yield of HMF compared to other ionic liquids. Furthermore, over 60% yields of HMF from fructose were obtained in all catalysts (Cr-K10, Ni₂P/Cr-K10 and Ni₂P mixed with Cr-K10) at 120 °C within 1.5 h, while the HMF yields from glucose were unsatisfyingly achieved. This suggested that the synthesized Ni₂P/Cr-K10 is found to be a good catalyst and can be potentially applicable for further conversion to other value-added chemicals in the next step.