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

Abstract

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 (Ov) concentration, which could offer a satisfactory FDCA yield of 96% using air as the oxygen source (130 °C, 1.5 MPa air, 3 h). Remarkably, Mn3Co2O x –0.3VC offered an outstanding FDCA formation rate of 2611 μmolFDCA·gcat –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 Ov concentration exhibits a weaker Mn–O bond intensity, which brings about a higher lattice oxygen (OL) reactivity. More importantly, density functional theory (DFT) calculations also demonstrate that increasing the Ov amount not only boosts the OL reactivity of the catalyst by reducing the formation energy of Ov but also contributes to the adsorption and activation of O2 over the catalyst by significantly cutting down the O2 adsorption energy, thus leading to an enhanced catalytic activity for the oxidation of HMF. Besides, the catalyst with a higher Ov concentration provides a stronger substrate adsorption ability, which may also promote the HMF oxidation reactions. This work provides insights into the role of Ov over Mn-based oxides in oxidation catalysis by a Mars–van Krevelen mechanism.

Enabling Efficient Aerobic 5‐Hydroxymethylfurfural Oxidation to 2,5‐Furandicarboxylic Acid in Water by Interfacial Engineering Reinforced Cu−Mn Oxides Hollow Nanofiber

“…On the other hand, the state of lattice oxygen in the composite oxides affords a certain variation in the different comparative catalysts. It is generally believed that the higher binding energy of lattice oxygen is beneficial to improve catalyst oxidation activity [7b,16] . Besides, lattice oxygen can effectively provide base sites and facilitate the adsorption and activation of reaction substrates, which might be reinforced by the formed interfacial engineering effect [7b] .…”

“…It is generally believed that the higher binding energy of lattice oxygen is beneficial to improve catalyst oxidation activity [7b,16] . Besides, lattice oxygen can effectively provide base sites and facilitate the adsorption and activation of reaction substrates, which might be reinforced by the formed interfacial engineering effect [7b] . We also extracted the surface elemental proportion from the collected XPS result summarized in Table S2.…”

“…To our knowledge, the Mars‐van Krevelen (MvK) mechanism is generally acknowledged in the catalytic oxidation of HMF over spinel oxides (Scheme 2). [1b,7b] The modified MvK mechanism was employed for depicting surface oxygen mobility of catalyst as follows: (1) The lattice oxygen O L can interact with HMF molecule and make the HMF be oxidized into corresponding oxidized products as evidenced by the aforementioned control experiments, while the free oxygen molecule can be captured by existed oxygen vacancies O V to regenerate new O L . In the reaction process, the surface oxygen mobility was accompanied by the oxidation and reduction of the neighboring metal atoms with different oxidation states and the regeneration of oxygen vacancies O V .…”

“…This inspires us to rationally optimize the lattice oxygen activity in the transition metal oxides for obtaining enhanced catalytic performance. On the other hand, the regeneration of active oxygen in metal oxide still depends on the formed oxygen vacancy for capturing free oxygen molecules [7b] . Therefore, regulating the rational proportion of active lattice oxygen to oxygen vacancy in the catalyst can facilitate the consumption and regeneration cycle of lattice oxygen.…”

Current Advances in the Sustainable Conversion of 5‐Hydroxymethylfurfural into 2,5‐Furandicarboxylic Acid

“…In any case, the combination of Mn and Co proved the most effective among those reported till now. Indeed, Liu et al [42] described the preparation of vitamin C-assisted mesoporous MnÀ Co spinel oxides obtained by solid-state grinding and its use in HMF oxidation in air. This approach was fully sustainable and very innovative, as well as easily scalable at the industrial level.…”