Iron Oxide Encapsulated by Ruthenium Hydroxyapatite as Heterogeneous Catalyst for the Synthesis of 2,5-Diformylfuran

Magnetic gamma-Fe2O3 nanocrystallites encapsulated by hydroxyapatite (HAP), HAP@gamma-Fe2O3, were prepared followed by cation exchange of Ca2+ on the external HAP surface with Ru3+ to give the gamma-Fe2O3@HAP-Ru catalyst. The structure of the as-prepared catalyst was characterized, and its catalytic activity was studied in the aerobic oxidation of 5-hydroxymethylfurfural (HMF). gamma-Fe2O3@HAP-Ru showed a high catalytic activity for the aerobic oxidation of HMF into 2,5-diformylfuran (DFF). A high DFF yield of 89.1% with an HMF conversion of 100% was obtained after 4 h at 90 degrees C. Importantly, the synthesis of DFF from fructose was realized by two consecutive steps. The dehydration of fructose in the presence of a magnetic acid catalyst (Fe3O4@SiO2-SO3H) produced HMF in a yield of 90.1 %. Then the Fe3O4@SiO2-SO3H catalyst was removed from the reaction solution with a permanent magnet, and HMF in the resulting solution was further oxidized to DFF with a yield of 79.1% based on fructose. The synthesis of DFF from fructose by two steps avoids the tedious separation of the intermediate HMF, which saves time and energy.