Kinetic and structural understanding of bulk and supported vanadium-based catalysts for furfural oxidation to maleic anhydride

Abstract

The kinetics of gas-phase furfural partial oxidation to maleic anhydride (MA) was studied over bulk vanadium–phosphorus-based catalysts obtained by aqueous (VPAq) and organic (VPOr) methods and compared to a supported V₂O₅/Al₂O₃ catalyst. The solids were characterized by N₂ adsorption–desorption, XRD and UV-vis DRS. Results showed a higher specific surface area on VPOr compared with VPAq materials, with a well-defined (VO)₂P₂O₇ crystalline structure. UV-vis analysis showed mainly V(V) on VPAq and an intermediate state between V(IV) and V(V) on VPOr. A detailed kinetic study demonstrated that furfural can be oxidized to MA or CO_x through parallel paths. At high oxygen partial pressures MA oxidation is inhibited on VPO catalysts but favored on V₂O₅/Al₂O₃. A Langmuir–Hinshelwood kinetic model with negligible site occupancy fits the experimental data with a 16% mean error. It also shows a higher apparent activation energy for furfural partial oxidation than for complete oxidation, highlighting the favored selectivity to maleic anhydride at higher temperatures on VPO catalysts.