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

Insight into the Critical Role of Oxygen Vacancies and V=O Bonds Length in V2O5 for Advanced Zinc Ion Storage

Due to the larger sizes and stronger positive polarity of Zn2+ than dominant univalent ions, Zn2+ sluggish diffusion within V2O5 host electrodes is an essential issue in developing aqueous zinc-ion batteries (ZIBs) of higher energy densities. Herein, a high-performance V2O5 cathode was developed through subtly synthesizing and tuning V2O5 with oxygen vacancies-enriched and elongated apical V=O1 bond by altering the gradient concentration of hydrazine hydrate in the gas-solid reaction system. This strategy can enhance both intrinsic and extrinsic conductivity to a large extent. The electrochemical testing demonstrated the oxygen vacancies-enriched and elongated apical V=O1 bond can not only increase the intrinsic electronic conductivity of V2O5, but also induce additional pseudocapacitance to enhance the Zn2+ diffusion kinetics. We used infrared spectroscopy and Raman spectroscopy to characterize the change in the bond length structure of V2O5. Simultaneously, the long-term cyclability (capacity retention of 76.9 % after 1200 cycles at 4.0 A g-1) and rate capabilities (218 mAh g-1 at 4.0 A g-1) are promoted as well. We believe that our work might shed light on the bond length engineering of V2O5 and provide insights for the reasonable designing of novel cathodes for practical rechargeable ZIBs.

Crystal phase-driven performance of MnO2 in aqueous phase low-temperature thermal catalysis: Synergistic interactions between Mn3+ and surface lattice oxygen

Catalytic oxidation at mild conditions is crucial for mitigating the high pressure and high temperature challenges associated with current catalytic wet air oxidation (CWAO) technologies in wastewater treatment. Among potential materials for catalytic oxidation reactions, polycrystalline MnO2 existed in natural minerals holds considerable promise. However, the relationships between different crystal phases of MnO2 and their catalytic activity sources in aqueous phase remain uncertain and subject to debate. In this research, we synthesized various MnO2 crystal phases, comprising α-, β-, δ-, γ-, ε-, and λ-MnO2, and assessed their catalytic oxidation efficiency during low-temperature heating for treatment of organic pollutants. Our findings demonstrate that λ-MnO2 exhibits the highest catalytic activity, followed by δ-MnO2, γ-MnO2, α-MnO2, ε-MnO2, and β-MnO2. The variations in catalytic activity among different MnO2 are attributed to variances in their oxygen vacancy abundance and redox activity. Furthermore, we identified the primary active species, which include Mn3+ and superoxide radicals (•O2-) generated by surface lattice oxygen of MnO2. This research highlights the critical role of crystal phases in influencing oxygen vacancy content, redox activity, and overall catalytic performance, providing valuable insights for the rational design of MnO2 catalysts tailored for effective organic pollutant degradation in CWAO applications.

Quasi-MOF-Engineered MnOx/CeBTC Multinanozyme as a Robust Self-Cascade ROS Generator toward Antibacterial Face Mask

It is of great importance to endow personal protective equipments with bactericidal property combating against infected pathogens. Nanozyme that can generate reactive oxygen species (ROS) in an enzyme-catalytic manner is regarded as a novel and promising nanobactericide. But until now, very rare of them is designed specifically for personal protective equipments. In this study, a multinanozyme of manganese oxide supported on Ce-containing MOF (CeBTC) is constructed with post-engineering via a quasi-metal-organic framework (MOF) strategy (denoted as MnOx/q-CeBTC). The strategy enables a full exposure of the metal cluster nodes, introduction of new active Mn─O─Ce bonds and strengthens interaction between the metal nodes and the guest oxide. As an advanced multinanozyme, the MnOx/q-CeBTC exhibits excellent multiple enzymatic activities at low temperature, and enables abundant and self-cascade ROS generation without H2O2 addition. This empowers it with high efficiency in bacteria killing, which is also reflected when incorporated into face mask to combat against pathogen invasion even at low temperature. The results achieved in this work provide guidance for rational design of effective bactericide based on nanozyme and broaden their application in personal protective equipment and other fields.

Dimethyl Carbonate Synthesis from CO2 over CeO2 with Electron-Enriched Lattice Oxygen Species

Direct synthesis of dimethyl carbonate (DMC) from CO2 plays an important role in carbon neutrality, but its efficiency is still far from the practical application, due to the limited understanding of the reaction mechanism and rational design of efficient catalyst. Herein, abundant electron-enriched lattice oxygen species were introduced into CeO2 catalyst by constructing the point defects and crystal-terminated phases in the crystal reconstruction process. Benefitting from the acid-base properties modulated by the electron-enriched lattice oxygen, the optimized CeO2 catalyst exhibited a much higher DMC yield of 22.2 mmol g-1 than the reported metal-oxide-based catalysts at the similar conditions. Mechanistic investigations illustrated that the electron-enriched lattice oxygen can provide abundant sites for CO2 adsorption and activation, and was advantageous of the formation of the weakly adsorbed active methoxy species. These were facilitating to the coupling of methoxy and CO2 for the key *CH3OCOO intermediate formation. More importantly, the weakened adsorption of *CH3OCOO on the electron-enriched lattice oxygen can switch the rate-determining-step (RDS) of DMC synthesis from *CH3OCOO formation to *CH3OCOO dissociation, and lower the corresponding activation barriers, thus giving rise to a high performance. This work provides insights into the underlying reaction mechanism for DMC synthesis from CO2 and methanol and the design of highly efficient catalysts.

Highly Reversible Zn-Air Batteries Enabled by Tuned Valence Electron and Steric Hindrance on Atomic Fe-N4-C Sites

The bifunctional oxygen electrocatalyst is the Achilles' heel of achieving robust reversible Zn-air batteries (ZABs). Herein, durable bifunctional oxygen electrocatalysis in alkaline media is realized on atomic Fe-N4-C sites reinforced by NixCo3-xO4 (NixCo3-xO4@Fe1/NC). Compared with that of pristine Fe1/NC, the stability of the oxygen evolution reaction (OER) is increased 10 times and the oxygen reduction reaction (ORR) performance is also improved. The steric hindrance alters the valence electron at the Fe-N4-C sites, resulting in a shorter Fe-N bond and enhanced stability of the Fe-N4-C sites. The corresponding solid-state ZABs exhibit an ultralong lifespan (>460 h at 5 mA cm-2) and high rate performance (from 2 to 50 mA cm-2). Furthermore, the structural evolution of NixCo3-xO4@Fe1/NC before and after the OER and ORR as well as charge-discharge cycling is explored. This work develops an efficient strategy for improving bifunctional oxygen electrocatalysis and possibly other processes.

Sunlight-driven and gram-scale vanillin production via Mn-defected γ-MnO2 catalyst in aqueous environment

The production of vanillin from biomass offers a sustainable route for synthesizing daily-use chemicals. However, achieving sunlight-driven vanillin synthesis through H2O activation in an aqueous environment poses challenges due to the high barrier of H2O dissociation. In this study, we have successfully developed an efficient approach for gram-scale vanillin synthesis in an aqueous reaction, employing Mn-defected γ-MnO2 as a photocatalyst at room temperature. Density functional theory calculations reveal that the presence of defective Mn species (Mn3+) significantly enhances the adsorption of vanillyl alcohol and H2O onto the surface of the γ-MnO2 catalyst. Hydroxyl radical (˙OH) species are formed through H2O activation with the assistance of sunlight, playing a pivotal role as oxygen-reactive species in the oxidation of vanillyl alcohol into vanillin. The Mn-defected γ-MnO2 catalyst exhibits exceptional performance, achieving up to 93.4% conversion of vanillyl alcohol and 95.7% selectivity of vanillin under sunlight. Notably, even in a laboratory setting during the daytime, the Mn-defected γ-MnO2 catalyst demonstrates significantly higher catalytic performance compared to the dark environment. This work presents a highly effective and promising strategy for low-cost and environmentally benign vanillin synthesis.

Coupled Interface and Oxygen-Defect Engineering in Co3O4/CoMoO4 Heterostructures toward Active Oxidation of Ethylbenzene

The catalytic oxidation of ethylbenzene (EB) is a promising route to produce acetophenone (AcPO). Unfortunately, it remains a great challenge to achieve the highly efficient oxidation of EB under solvent-free conditions using molecular oxygen as the sole oxidant. In this contribution, we present a facile strategy to construct hierarchical oxygen vacancy-rich Co3O4/CoMoO4 heterostructures (Vö-CCMO), which delivers a high yield value of 74.5% at 83.2% conversion of EB and selectivity of 89.6% to AcPO. Both experimental studies and theoretical calculations substantiate the important role of oxygen-defect engineering triggered by the modified chemistry environment at the interfaces between the biphasic phases, which contributes to the good catalytic performance. This work illustrates a promising paradigm for the exploit of advanced catalysts toward boosting EB oxidation reaction in a more practical way.

Enhancing Low-Potential Electrosynthesis of 2,5-Furandicarboxylic Acid on Monolithic CuO by Constructing Oxygen Vacancies

Electrosynthesis of 2,5-furandicarboxylic acid (FDCA) from the biomass-derived 5-hydroxymethylfurfural (HMF) is one of the most potential means to produce a bioplastic monomer. Copper oxide (CuO) catalyst shows promising prospects due to its high surface activity, conductivity, and stability, but relatively poor capability of oxygen evolution; however, the weak adsorption of substrates and the lack of facile synthetic strategies largely restrict its practical application. Here, a novel facile in situ method, alternate cycle voltammetry (denoted as c) and potentiostatic electrolysis (denoted as p), was proposed to prepare a monolithic cpc-CuO/Cu-foam electrocatalyst. Along with the increment of CuO and its surficial oxygen vacancies (OV), the FDCA yield, productivity, and Faradaic efficiency can reach up to ∼98.5%, ∼0.2 mmol/cm2, and ∼94.5% under low potential of 1.404 VRHE. Such an efficient electrosynthesis system can be easily scaled up to afford pure FDCA powders. In a combinatory analysis via electron paramagnetic resonance spectroscopy, H2 temperature-programmed reduction, open circuit potential, infrared spectroscopy, zeta potential, electrochemical measurement, and theoretical calculation, we found that the CuO was the active phase and OV generated on CuO surface can dramatically enhance the adsorption of *HMF and *OH (* denotes an active site), accounting for its superior FDCA production. This work offers an excellent paradigm for enhancing biomass valorization on CuO catalysts by constructing surficial defects.

Regulating oxygen vacancies and hydroxyl groups of α-MnO2 nanorods for enhancing post-plasma catalytic removal of toluene

Although nonthermal plasma (NTP) technology has high removal efficiency for volatile organic compounds (VOCs), it has limited carbon dioxide (CO2) selectivity, which hinders its practical application. In this study, α-MnO2 nanorods with tunable oxygen vacancies and hydroxyl groups were synthesized by two-step hydrothermal process to enhance their activity for deep oxidation of toluene. Hydrochloric acid (HCl) was used to assist in synthesis of α-MnO2 nanorods with tunable oxygen vacancies, furtherly, more hydroxyl groups were introduced to HCl-assisted synthesized α-MnO2 by K+ supplement. The results showed that the as-synthesized nanorods exhibited superior activity, improved by nearly 30% removal efficiency of toluene compared to pristine MnO2 at SIE = 339 J/L, and reaching high COx selectivity of 72% at SIE = 483 J/L, successfully promoting the deep oxidation of toluene. It was affirmed that oxygen vacancies played an important role in toluene conversion, improving the conversion of ozone (O3) and resulting in higher mobility of surface lattice oxygen species. Besides, the enhancement of deep oxidation performance was caused by the increase of hydroxyl groups concentration. In-situ DRIFTS experiments revealed that the adsorbed toluene on catalyst surface was oxidized to benzyl alcohol by surface lattice oxygen, and hydroxyl groups were also found participating in toluene adsorption. Overall, this study provides a new approach to designing catalysts for deep oxidation of VOCs.

3D π-d Conjugated Coordination Polymer Enabling Ultralong Life Magnesium-Ion Storage

There has been increasing interests in π-d conjugated coordination polymers (CCPs) for energy storage because of their rapid charge transfer through long-range planar π-d conjugation between ligands and metal centers. Nevertheless, currently reported CCPs for energy storage are mostly based on 1D or 2D structures. There are few 3D CCPs reported to date because of the great challenge in constructing nonplanar coordination geometries, let alone their applications in multivalent ions storage. Herein, a triphenylene-catecholate-based 3D CCP (Mn-HHTP) is successfully synthesized assembled from the multidentate chelating groups of hexahydroxytriphenylene (HHTP) ligands and their isotropic coordination with Mn2+ ions. The 3D conjugated structure of Mn-HHTP enables an exceptional cycle life of >4000 cycles at 0.5 A g-1 for multivalent Mg2+ ion storage, which is far superior to most organic and inorganic electrode materials. Experimental characterizations combined with theoretical calculations indicate that the semiquinone radicals at the HHTP ligands are the electroactive centers for Mg2+ ions storage. The excellent performance of Mn-HHTP opens a new avenue towards the design of 3D CCPs for long-life rechargeable magnesium-ion batteries.

Oxygen Vacancy-Induced Metal-Support Interactions in AuPd/ZrO2 Catalysts for Boosting 5-Hydroxymethylfurfural Oxidation

The construction of strong metal-support interactions in oxide-supported noble metal nanocatalysts has been considered an emerging and efficient way in improving catalytic performance in biomass-upgrading reactions. Herein, a citric acid (CA)-assisted synthesized ZrO2 layer with improved oxygen vacancy (Ov) concentrations on a natural clay mineral of halloysite nanotubes (HNTs) was designed. Moreover, AuxPdy/ZrO2@HNTs-zCA catalysts were prepared by loading AuPd bimetal and employed for aerobic oxidation of the lignocellulosic biomass-derived 5-hydroxymethylfurfural (HMF) platform to the bioplastic monomer 2,5-furandicarboxylic acid (FDCA) with water as the solvent. The results of catalytic experiments revealed that the Au3Pd1/ZrO2@HNTs-1.0CA catalyst exhibited excellent catalytic activity at 0.5 MPa O2, with a satisfactory FDCA yield of 99.5% and outstanding FDCA formation rate of 1057.9 mmol·g-1·h-1. The improved Ov concentration in the ZrO2 support enhanced the adsorption and activation ability of the catalyst for O2, and a higher Lewis acid concentration provided a stronger adsorption ability of the catalyst for reaction substrates. Besides, the synergistic effect of AuPd bimetallic nanoparticles steered the tandem oxidation of aldehyde and alcohol groups in HMF and accelerated the rate-determining step. More importantly, the relationship between the Ov concentration and catalytic performance also demonstrated that the enhanced catalytic activity for HMF oxidation was mainly attributed to the active interface of AuPd-ZrOx. This work offers fresh insights into rationally designing oxygen vacancy-driven strong interactions between the oxide support and noble nanoparticles for the catalytic upgrade of biomass platform chemicals.

Titanium Oxide Electrocatalytic Membrane Filtration: "Two Faces" of Oxygen Vacancies in Generation and Transformation of Reactive Oxygen Species

Oxygen vacancies are crucial to the production of reactive oxygen species (ROS) in the metal oxide electrocatalytic membrane (MOx EM) process. Here, using cathodic TiOx EM as a model, we thoroughly reveal the roles of oxygen vacancies in ROS generation and transformation. Oxygen vacancies significantly promote H2O2 and •OH production at low concentrations (increment <35%) but inhibit their production at high concentrations (increment >35%). Electrochemical analysis discloses that the enhancement of ROS production profits from the acceleration of charge transfer kinetics by both bulk and surface oxygen vacancies, whereas we attribute the decline in ROS production to the strong adsorption of ROS by surface oxygen vacancies. It is strongly supported by theoretical calculations that reveal the promoted adsorption of *OOH and *OH by oxygen vacancies, which intensifies the capture and scavenging of H2O2 and •OH. Moreover, the gradual increase of interaction time between ROS and oxygen vacancies (from ∼1 to ∼5 s) notably reduces the generation and transformation efficiency of ROS, further highlighting the detrimental impact of oxygen vacancies. In summary, oxygen vacancies show "two faces" toward ROS generation and transformation, acting as ROS promoters at low concentrations but inhibitors at high concentrations. A medium oxygen vacancy concentration is preferred for ROS production, thus causing impressive pollutant removal (>95% removal of bisphenol A within 1.2-1.5 s at 360-440 LMH). This study provides guidance on regulating ROS generation and transformation by manipulating the oxygen vacancy concentration to enhance the decontamination efficiency of MOx EMs.

Effect of MnO2 Crystal Type on the Oxidation of Furfural to Furoic Acid

The base-free oxidation of furfural by non-noble metal systems has been challenging. Although MnO2 emerges as a potential catalyst application in base-free conditions, its catalytic efficiency still needs to be improved. The crystalline form of MnO2 is an important factor affecting the oxidation ability of furfural. For this reason, four crystalline forms of MnO2 (α, β, γ, and δ-MnO2) were selected. Their oxidation performance and surface functional groups were analyzed and compared in detail. Only δ-MnO2 exhibited excellent activity, achieving 99.04% furfural conversion and 100% Propo.FA (Only furoic acid was detected by HPLC in the product) under base-free conditions, while the furfural conversion of α, β, and γ-MnO2 was below 10%. Characterization by XPS, IR, O2-TPD and other means revealed that δ-MnO2 has the most abundant active oxygen species and surface hydroxyl groups, which are responsible for the best performance of δ-MnO2. This work achieves the green and efficient oxidation of furfural to furoic acid over non-noble metal catalysts.

Photothermal CO-PROX reaction over ternary CuCoMnOx spinel oxide catalysts: the effect of the copper dopant and thermal treatment

The purification of carbon monoxide in H₂-rich streams is an urgent problem for the practical application of fuel cells, and requires the development of efficient and economical catalysts for the preferential oxidation of CO (CO-PROX). In the present work, a facile solid phase synthesis method followed by an impregnation method were adopted to prepare a ternary CuCoMnO_x spinel oxide, which shows superior catalytic performance with CO conversion of 90% for photothermal CO-PROX at 250 mW cm^-2. The dopant of copper species leads to the incorporation of Cu ions into the CoMnO_x spinel lattice forming a ternary CuCoMnO_x spinel oxide. The appropriate calcination temperature (300 °C) contributes to the generation of abundant oxygen vacancies and strong synergetic Cu-Co-Mn interactions, which are conducive to the mobility of oxygen species to participate in CO oxidation reactions. On the other hand, the highest photocurrent response of CuCoMnO_x-300 also promotes the photo-oxidation activity of CO due to the high carrier concentration and efficient carrier separation. In addition, the in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) confirmed that doping copper species could enhance the CO adsorption capacity of the catalyst due to the generation of Cu⁺ species, which significantly increased the CO oxidation activity of the CuCoMnO_x spinel oxide. The present work provides a promising and eco-friendly solution to remove the trace CO in H₂-rich gas over CuCoMnO_x ternary spinel oxide with solar light as the only energy source.

Boosting Chemoselective Hydrogenation of Nitroaromatic via Synergy of Hydrogen Spillover and Preferential Adsorption on Magnetically Recoverable Pt@Fe2 O3

It is highly desired but challenging to design high performance catalyst for selective hydrogenation of nitro compounds into amino compounds. Herein, a boosting chemoselective hydrogenation strategy on Pt@Fe₂ O₃ is proposed with gradient oxygen vacancy by synergy of hydrogen spillover and preferential adsorption. Experimental and theoretical investigations reveal that the nitro is preferentially adsorbed onto oxygen vacancy of Pt@Fe₂ O₃ , meanwhile, the H₂ dissociated on Pt nanoparticles and then spillover to approach the nitro for selective hydrogenation (>99% conversion of 4-nitrostyrene, > 99% selectivity of 4-aminostyrene, TOF of 2351 h^-1 ). Moreover, the iron oxide support endows the catalyst magnetic retrievability. This high activity, selectivity, and easy recovery strategy provide a promising avenue for selective hydrogenation catalysis of various nitroaromatic.

Oxidative Cleavage and Ammoxidation of Unsaturated Hydrocarbons via Heterogeneous Auto-Tandem Catalysis

The oxidative cleavage and functionalization of unsaturated C-C bonds are important processes for synthesis of carbonyl compounds from hydrocarbon feedstocks, yet there has been no report of direct amidation of unsaturated hydrocarbons via an oxidative cleavage of unsaturated C-C bonds with molecular oxygen as an environmentally benign oxidant. Herein, for the first time, we describe a manganese oxide-catalyzed auto-tandem catalysis strategy that enables direct synthesis of amides from unsaturated hydrocarbons by coupling oxidative cleavage with amidation. With oxygen as an oxidant and ammonia as a nitrogen source, a wide range of structurally diverse mono- and multisubstituted activated and unactivated alkenes or alkynes can smoothly undergo unsaturated C-C bond cleavage to deliver one- or multiple-carbon shorter amides. Moreover, a slight modification of the reaction conditions also allows for the direct synthesis of sterically hindered nitriles from alkenes or alkynes. This protocol features excellent functional group tolerance, a broad substrate scope, flexible late-stage functionalization, facile scalability, and a cost-effective and recyclable catalyst. Detailed characterizations reveal that the high activity and selectivity of the manganese oxides are attributed to the large specific surface area, abundant oxygen vacancies, better reducibility, and moderate acid sites. Mechanistic studies and density functional theory calculations indicate that the reaction proceeds through divergent pathways depending on the structure of substrates.

Yttrium-modified Co3O4 as efficient catalysts for toluene and propane combustion: Effect of yttrium content

A series of Y-modified cobalt oxides with various Y/(Co+Y) molar ratios (0.25 %, 0.5 %, 1 %, 3 % and 5 %) were prepared to study the effect of Y content on toluene and propane combustion. The characterization of the catalysts revealed that proper Y incorporation resulted in smaller crystallite sizes, larger specific surface areas, more oxygen vacancies and weaker Co-O bonds. As such, the Y-modified Co₃O₄ showed enhanced low-temperature reducibility, boosted oxygen mobility and better catalytic activity. However, excess Y (> 1 %) aggregates on the surface of Co₃O₄ and forms yttrium carbonate species, hindering the catalyst activity. A volcano-type relationship between the Y content and the catalytic activity was established. The optimal catalyst 1 % Y-Co (with Y/(Co+Y) molar ratio of 1 %) exhibited toluene oxidation rate of 24 nmol g^-1 s^-1 at 220 °C and propane oxidation rate of 69 nmol g^-1 s^-1 at 180 °C. Besides, 1 % Y-Co presented perfect cycling stability and long-term durability in propane oxidation. Regarding its low cost, high efficiency and good stability, 1 % Y-Co is a promising catalyst for the practical elimination of hydrocarbon emissions.

Leveraging Pt/Ce1-xLaxO2-δ To Elucidate Interfacial Oxygen Vacancy Active Sites for Aerobic Oxidation of 5-Hydroxymethylfurfural

The interfacial oxygen-defective sites of oxide-supported metal catalysts are generally regarded as active centers in diverse redox reactions. Identification of their structure-property relationship at the atomic scale is of great importance but challenging. Herein, a series of La³⁺-doped three-dimensionally ordered macroporous CeO₂ (3D-Ce_1-xLa_xO_2-δ) were synthesized and applied as supports for Pt nanoparticles. The pieces of evidence from a suite of in-situ/ex-situ characterizations and theoretical calculations revealed that the La³⁺-mono-substituted La-□(-Ce)₂ sites (where □ represents an oxygen vacancy) exhibited superior charge transfer ability, behaving as trapping centers for Pt nanoparticles. The resulting interfacial Pt^δ+/La-□(-Ce)₂ sites served as the reversible active species in the aerobic oxidation of 5-hydroxymethylfurfural to boost catalytic performance by simultaneously promoting oxygen activated capacity and the cleavage of O-H/C-H bonds of adsorbed hydroxymethyl groups. Consequently, the Pt/3D-Ce_0.9La_0.1O_2-δ catalyst possessing the highest number of Pt^δ+/La-□(-Ce)₂ sites showed the best catalytic performance with 99.6% yield to 2,5-furandicarboxylic acid in 10 h. These results offer more insights into the promoting mechanism of interfacial oxygen-defective sites for the liquid-phase aerobic oxidation of aldehydes and alcohols.

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

Herein, a one-dimensional hollow nanofiber catalyst composed of tightly packed multiphase metal oxides of Mn₂ O₃ and Cu_1.4 Mn_1.6 O₄ was constructed by electrospinning and tailored thermal treatment procedure. The characterization results comprehensively confirmed the special morphology and composition of various comparative catalysts. This strategy endowed the catalyst with abundant interfacial characteristics of components Mn₂ O₃ and Cu_1.4 Mn_1.6 O₄ nanocrystal. Impressively, the tuning thermal treatment resulted in tailored Cu^I sites and surface oxygen species of the catalyst, thus affording optimized oxygen vacancies for reinforced oxygen adsorption, while the concomitant enhanced lattice oxygen activity in the constructed composite catalyst ensured the higher catalytic oxidation ability. More importantly, the regulated proportion of oxygen vacancy and lattice oxygen in the composite catalyst was obtained in the best catalyst, beneficial to accelerate the reaction cycle. Compared to other counterparts obtained by different temperatures, the CMO-500 sample exhibited superior selective aerobic 5-hydroxymethylfurfural (HMF) oxidation to 2,5-furandicarboxylic acid (FDCA, 96 % yield) in alkali-bearing aqueous solution using O₂ at 120 °C, which resulted from the above-mentioned composition optimization and interfacial engineering reinforced surface oxygen consumption and regeneration cycle. The reaction mechanism was further proposed to uncover the lattice oxygen and oxygen vacancy participating HMF conversion process.

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

2,5-Furandicarboxylic acid (FDCA) is currently considered one of the most relevant bio-sourced building blocks, representing a fully sustainable competitor for terephthalic acid as well as the main component in green polymers such as poly(ethylene 2,5-furandicarboxylate) (PEF). The oxidation of biobased 5-hydroxymethylfurfural (HMF) represents the most straightforward approach to obtain FDCA, thus attracting the attention of both academia and industries, as testified by Avantium with the creation of a new plant expected to produce 5000 tons per year. Several approaches allow the oxidation of HMF to FDCA. Metal-mediated homogeneous and heterogeneous catalysis, metal-free catalysis, electrochemical approaches, light-mediated procedures, as well as biocatalytic processes share the target to achieve FDCA in high yield and mild conditions. This Review aims to give an up-to-date overview of the current developments in the main synthetic pathways to obtain FDCA from HMF, with a specific focus on process sustainability.

Control in Local Coordination Environment Boosting Activating Molecular Oxygen with an Atomically Dispersed Binary Mn-Co Catalyst

Activation of molecular oxygen plays a crucial role in natural organisms and the modern chemical industry. Herein, we report a Mn-Co dual-single-atom catalyst that exerts a specific synergy in boosting O₂ activation by collaboration between two distinct types of activation sites. Taking the oxidative esterification of the biomass platform 5-hydroxymethylfurfural (HMF) as the model reaction, the activation of O₂ is demonstrated through transforming O₂ into a reactive superoxide anion radical (O₂^•-) on Co-N₄ sites and, meanwhile, by reversible consumption and supplement of coordinated surface oxygen as a new type of reactive oxygen species (ROS) on N,O-coordinated single-atom Mn sites (Mn-N_xO_y). EXAFS analysis results show a longer average Mn-O bond distance at near 2.19 Å, which makes the breaking and formation of surface Mn-O bonds easier to cycle. Control experiments support that such Mn-O bonding conditions could facilitate H-elimination of C-H in HMF. The co-existence of two types of ROS effectively matches the oxidation of hydroxyl and aldehyde groups, and thus, the overall reaction is boosted in excellent yield of diester (95.8%) with an extremely high carbon balance. This study represents a rare example of taking advantage of the synergy of the diatomic catalyst for activating O₂ by two types of activation pathways.

High-precision synthesis of α-MnO2 nanowires with controllable crystal facets for propane oxidation

α-MnO2 nanowires with different crystal facets were synthesized. The (110) crystal facet of α-MnO2 is conducive to propane catalysis, due to the lowest electron energy, effectively Mn valence adjustment and abundant oxygen vacancies.