Solid-state synthesis of CN-encapsulated CoFe alloy catalysts for mild HMF oxidation to FDCA: insights into the kinetics and mechanism

The efficient and environmentally friendly oxidation of biomass-based HMF to FDCA under mild conditions is highly desirable yet challenging. In this study, a series of CoFe alloy catalysts encapsulated in porous carbon (Co_xFe_y@NC) were synthesized using a solid-state synthesis method. By adjusting the Co/Fe ratio, an FDCA yield of 96.1% was achieved with the optimal Co₂Fe₁@NC catalyst, which exhibited an impressive FDCA formation rate of 0.428 mmol_FDCA g_cat^-1 h^-1 at 100 °C and 0.5 MPa O₂, surpassing the performance of its monometallic Fe or Co counterparts. Experimental and kinetics observations demonstrated that the presence of the CoFe alloy significantly enhanced the HMF oxidation rate and shifted the rate-determining step from HMFCA oxidation to FFCA oxidation when compared to the Co@NC catalyst. Additionally, the CoFe alloy facilitated the adsorption/activation of both substrates and oxygen, synergistically working with the support material to lower the reaction energy barriers and enhance FDCA formation. This study presents a novel and environmentally friendly approach for designing efficient Co-based catalysts for complex tandem oxidation reactions.