Enhanced catalysis of a vanadium-substituted Keggin-type polyoxomolybdate supported on the M 3 O 4 /C (M = Fe or Co) surface enables efficient and recyclable oxidation of HMF to DFF.

In the reaction of oxidizing 5-hydroxymethylfurfural (HMF), attaining high efficiency and selectivity in the conversion of HMF into DFF presents a challenge due to the possibility of forming multiple products. Polyoxometalates are considered highly active catalysts for HMF oxidation. However, the over-oxidation of products poses a challenge, leading to decreased purity and yield. In this work, metal-organic framework-derived Fe 3 O 4 /C and Co 3 O 4 /C were designed as carriers for the vanadium-substituted Keggin-type polyoxomolybdate H 5 PMo 10 V 2 O 40 ·35H 2 O (PMo 10 V 2 ). In this complex system, spinel oxides can effectively adsorb HMF molecules and cooperate with PMo 10 V 2 to catalyze the aerobic oxidation of HMF. As a result, the as-prepared PMo 10 V 2 @Fe 3 O 4 /C and PMo 10 V 2 @Co 3 O 4 /C catalysts can achieve efficient conversion of HMF into DFF with almost 100% selectivity. Among them, PMo 10 V 2 @Fe 3 O 4 /C exhibits a higher conversion rate (99.1%) under milder reaction conditions (oxygen pressure of 0.8 MPa). Both catalysts exhibited exceptional stability and retained their activity and selectivity even after undergoing multiple cycles. Studies on mechanisms by in situ diffuse reflectance infrared Fourier transform spectroscopy and X-ray photoelectron spectroscopy revealed that the V 5+ and Mo 6+ in PMo 10 V 2 , together with the metal ions in the spinel oxides, act as active centers for the catalytic conversion of HMF. Therefore, it is proposed that PMo 10 V 2 and M 3 O 4 /C (M = Fe, Co) cooperatively catalyze the transformation of HMF into DFF via a proton-coupled electron transfer mechanism. This study offers an innovative approach for designing highly selective and recyclable biomass oxidation catalysts.