A phosphorus-doped carbon material derived from a sodium alginate/phosphoric acid hydrogel as an efficient catalyst for catalytic oxidation of furfural to maleic acid

Abstract

Sodium alginate is a biomass-derived polysaccharide. A novel hydrogel (SA–H₃PO₄) was prepared by taking advantage of the hydrogen bonding interactions between sodium alginate and phosphoric acid. Phosphoric acid molecules are highly dispersed in the hydrogel. A phosphorus-doped carbon material (PC-700) with a high content of P was derived through the calcination of the SA–H₃PO₄ xerogel under N₂ at 700 °C. PC-700 was used for the catalytic oxidation of furfural to maleic acid with the involvement of H₂O₂. The reaction route was investigated and 9 representative reactions for the reaction network were determined. The reaction rate constants and apparent activation energies of the reactions were obtained. Using the kinetic parameters, the kinetic models can simulate the concentration profiles in good agreement with the experimental data. Based on ample experimental results, the C₃PO species in PC-700 were identified as the active sites. The production of maleic acid from furfural over PC-700 is mainly achieved through the oxidation of furfural to 5-hydroxyfuran-2(5H)-one (HFONE) and the direct oxidation of furfural to maleic acid via β-formylacrylic acid (β-FA) formation. PC-700 has shown excellent catalytic activity for the production of maleic acid from furfural in the presence of H₂O₂. For the oxidation of 1000 mM furfural, a maleic acid yield of 74.8% and furfural conversion of 100% were obtained at 80 °C within 5 h.