Palygorskite-supported ruthenium catalysts for the efficient selective oxidation of 5-hydroxymethylfurfural to 2, 5-diformylfuran

The oxidation of 5-hydroxymethylfurfural (HMF) to 2, 5-diformylfuran (DFF) is an important reaction for the conversion of renewable biomass into feedstock chemicals. In this work, palygorskite (Pal)-supported ruthenium (Ru) catalysts were developed for the efficient selective oxidation of HMF to DFF. Using natural clay mineral palygorskite as the support enabled the immobilization and dispersion of Ru nanoparticles. A 100% HMF conversion, 98% DFF yield, and 98% DFF selectivity were obtained over Ru(III)/Pal catalyst after 4.5 h under the optimal reaction conditions at 110 °C and 10 bar of O₂ in toluene. Ru nanoparticles and palygorskite synergistically achieve the excellent catalytic performance of the catalyst. The Ru metal active sites facilitate the activation of the reactants or intermediates, accelerating the formation of DFF. Furthermore, due to their different particle sizes and Ru species, the Ru(III)/Pal catalyst exhibits higher catalytic activity than the Ru(0)/Pal catalyst for the oxidation of HMF to DFF. The palygorskite-enhanced dispersion effect on Ru nanoparticles augments the catalytic activity. Moreover, the palygorskite-supported Ru catalyst showed good stability and was reused for at least five times consecutive cycles without significant loss of its catalytic activity.