Vitamin C-Assisted Synthesized Mn-Co Oxides with Improved Oxygen Vacancy Concentration: Boosting Lattice Oxygen Activity for the Air-Oxidation of 5-(Hydroxymethyl)furfural

The catalytic oxidation of biomass-derived 5-(hydroxymethyl)furfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is a promising route to produce bioplastic monomers. Developing budget non-noble-metal catalysts for the efficient air-oxidation of HMF to FDCA is highly demanded but challenging. In this contribution, we present a facile and green vitamin C (VC)-assisted solid-state grinding method for synthesizing mesoporous Mn-Co spinel oxides with improved oxygen vacancy (O-v) concentration, which could offer a satisfactory FDCA yield of 96% using air as the oxygen source (130 degrees C, 1.5 MPa air, 3 h). Remarkably, Mn3Co2Ox-0.3VC offered an outstanding FDCA formation rate of 2611 mu mol(FDCA).g(cat)(-1).h(-1), which is the highest value achieved so far among ever-described Mn-based catalysts. Based on experimental studies, the catalytic performance of Mn-Co oxides for the oxidation of HMF corresponds well with their Mn-O bond intensities. The catalyst with a higher O-v concentration exhibits a weaker Mn-O bond intensity, which brings about a higher lattice oxygen (O-L) reactivity. More importantly, density functional theory (DFT) calculations also demonstrate that increasing the O-v amount not only boosts the O-L reactivity of the catalyst by reducing the formation energy of O-v but also contributes to the adsorption and activation of O-2 over the catalyst by significantly cutting down the O-2 adsorption energy, thus leading to an enhanced catalytic activity for the oxidation of HMF. Besides, the catalyst with a higher O-v concentration provides a stronger substrate adsorption ability, which may also promote the HMF oxidation reactions. This work provides insights into the role of O-v over Mn-based oxides in oxidation catalysis by a Mars-van Krevelen mechanism.

Automated summary

This study successfully synthesized mesoporous Mn-Co spinel oxides with improved oxygen vacancy concentration using a vitamin C-assisted method, which showed high FDCA yield. Experimental and density functional theory calculations demonstrated that increasing oxygen vacancy concentration enhances oxidant activation rate and substrate adsorption capability.