Activation Of Molecular Oxygen Research Articles

Water Enables Lattice Oxygen Activation of Transition Metal Oxides for Volatile Organic Compound Oxidation

A small amount of water can enhance the catalytic combustion activity of volatile organic compounds (VOCs) on transition metal oxides (TMOs), but its intrinsic mechanism is still controversial. Herein, we systematically demonstrate that water molecules can constantly activate lattice oxygen of transition metal oxides to form hydroxyl species theoretically and experimentally. The oxygen atoms of the generated hydroxyl species possess a weak bonding strength with circumjacent metal atoms to easily escape from the surface and attack electron-deficient carbon atoms of VOCs due to their comparatively stronger nucleophilicity, leaving abundant oxygen vacancies as the active sites for subsequent molecular oxygen activation. This work helps us deeply understand the role of water in lattice oxygen activation of transition metal oxides and provides direction for water-related catalysis, such as catalytic VOC combustion, water splitting, water–gas shift reactions, and corrosion.

Mechanistic insight into the charge carrier separation and molecular oxygen activation of manganese doping BiOBr hollow microspheres

High-efficiency separation of photogenerated charges and molecular oxygen activation is very important for photocatalytic removal of organic pollutants. However, the current understanding of the effect mechanism of metal substitution for the separation of photo-generated charges and molecular oxygen activation is still poor. Herein, efficient manganese (Mn)-doped BiOBr hollow microspheres synthesis, systematic characterizations, and theoretical calculation discovered that Mn-doping could not only induce produce oxygen vacancies (OVs), but also can act as active sites for catalytic reactions. The induced production of OVs and Mn2+/Mn3+ by Mn optimal doping introduced into BiOBr can synergistic promote the separation of photogenerated charges and molecular oxygen activation leads to significantly enhances degradation of crystal violet (CV). Upon analysis, Mn-doping introducing unsaturated d-orbital with bridging O2– formation π-donation accelerated the separation of photo-generated charges. Meanwhile, the larger overlap of Mn-3d orbitals with O2-2p orbitals forms a π-donation bond with charge transfer from metal to O2 leading to the oxygen–oxygen (OO) bond length and molecular oxygen activation. Finally, we proposed a possible mechanism to explain the highly efficient photocatalytic degradation performance of the acquired photocatalysts. This study provides not only a novel strategy for the rational design of highly active photocatalysts, but also in-depth insights into the separation of photo-generated charges and molecular oxygen activation.

A P450 Harboring Manganese Protoporphyrin IX Generates a Manganese Analogue of Compound I by Activating Dioxygen

The self-sufficient cytochrome P450 102A1 (P450BM3), known for its highly efficient activation of molecular oxygen, was reconstituted with manganese protoporphyrin IX. This artificial enzyme (Mn-BM3) was found to catalyze the monooxygenation of various substrates by activating molecular oxygen. Investigation using mechanistic probes (i.e., radical clock substrates) revealed that hydroxylation by Mn-BM3 proceeds via a radical intermediate of the substrate, supporting the involvement of an “H atom abstraction/•OH recombination” mechanism, which is the commonly accepted mechanism for hydroxylation by P450s. A DFT study also indicated that the activation barrier of Mn-porphine in the rebound step is higher than that of Fe-porphine, consistent with the experimental results obtained in the radical clock experiment, wherein Mn-BM3 presents a slower rebound rate than that of heme-bound BM3.

Generation of reactive chlorine species via molecular oxygen activation on a copper chloride loaded hydrothermal carbonaceous carbon for advanced oxidation process

In this study, we first achieve effective generation of reactive chlorine species (RCS) by molecular oxygen (O2) activation on a copper chloride loaded hydrothermal carbonaceous carbon (CuCl-HTCC). O2 can be adsorbed and activated by the cuprous (Cu(I)) from the CuCl-HTCC, and then converted into superoxide radical-hydrogen peroxide-hydroxyl radical, and chloride on the surface of CuCl-HTCC can be converted to RCS. This system holds two advantages: (1) plenty of Cu(I) exists in CuCl-HTCC can contribute to O2 activation heterogeneously. Its efficiency is much higher than that of homogeneous reactions in which Cu(I) cannot exist stably; (2) this process is a rapid heterogeneous process. Cu(I) can contribute to RCS generation with very fast kinetic through multi-steps. As a result, 10 mg/L of pollutants like phenol or ibuprofen were almost completely degraded in 120 min. This is a new and efficient method for generating RCS through the O2 activation process.

Activation of molecular oxygen by tenorite and ascorbic acid: Generation of high-valent copper species for organic compound oxidation

This study constructs a novel strategy for the activation of molecular oxygen over naturally abundant tenorite (CuO) complexed with ascorbic acid (AA). According to the results of ATR-FTIR characterization and DFT calculation, AA forms inner-sphere complexes with copper on the CuO surface (Cu(II)) in a monodentate mononuclear configuration, reduces Cu(II) to Cu(I), and complexes the latter species to efficiently activate molecular oxygen for the in situ production of H2O2 and subsequently generate reactive oxidants for the degradation of organic compounds. The multiple evidence of oxidant scavenging tests, EPR spectroscopy, molecular probe experiments, and XPS and XANES analyses collectively suggest that the dominant reactive oxidant is the surface-bound high-valent copper species (Cu(III)) rather than •OH. Compared with •OH, Cu(III) possesses the different oxidation behaviors for bisphenol A and benzoic acid and is less reactive toward alcohols and compounds with strongly electron-withdrawing groups and heterocyclic rings. The CuO/AA system exhibits stable performance that is only marginally affected by the water matrix and shows high durability in repetition tests. Thus, this work describes a promising strategy for the oxidation of organic contaminants via the activation of molecular oxygen and provides insights into the properties and identifications of the Cu(III) species.

Deep aerobic desulfurization of fuels over iron–сontaining zeolite based catalysts

Herein, we present a new approach to the design of the catalysts for aerobic oxidation of sulfur-containing compounds. Iron-containing zeolite-based (ZSM-5, ZSM-12) catalysts were synthesized and successfully tested in oxidation of model mixtures as well as real petroleum fractions. The catalysts were characterized by means of X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), scanning electron microscopy (SEM), ultraviolet–visible spectroscopy (UV/Vis), temperature programmed desorption of ammonia (NH3-TPD), and low-temperature nitrogen adsorption-desorption. Among these catalysts Fe-ZSM-12 demonstrated the best activity: exhaustive oxidation of dibenzothiophene (DBT) in the presence of this catalyst was achieved in 2 h at 150°C. Influence of the reaction conditions (temperature, amount of catalyst, and time) on the conversion of the model substrate was studied. It was shown that in the presence of Fe-ZSM-12 catalyst activation of molecular oxygen proceeds via formation of superoxide radical. Fe-ZSM-12 exhibited an excellent stability and retained its activity after 10 cycles of oxidation. Under optimal reaction conditions sulfur content in straight-run gasoline fraction was reduced from 807 to 43 ppm, in diesel fraction – from 1898 to 150 ppm. Two-dimensional GC-MS analysis of diesel fraction before and after desulfurization indicates high selectivity of the process. Possibility of sulfur dioxide formation during the aerobic oxidative desulfurization process was studied for the first time. The use of zeolite-based catalysts containing transition metals for aerobic oxidation of sulfur-containing compounds is a promising approach for clean fuel production.

Dual-function oxygen vacancy of BiOBr intensifies pollutant adsorption and molecular oxygen activation to remove tetracycline hydrochloride

Oxygen vacancy is an important factor for pollutant adsorption and molecular oxygen activation. How to construct the dual-function oxygen vacancy is still a challenge for environmental remediation. Here, BiOBr (3D-self-assembled nanospheres) with different contents of oxygen vacancies was prepared via solvothermal method and calcination, which intensified antibiotic adsorption and molecular oxygen activation to remove tetracycline hydrochloride. Adsorption experiments and theoretical calculations revealed that oxygen vacancies enhanced the adsorption of pollutants via ion exchange. Furthermore, surface complexation due to adsorption facilitated degradation through faster charge transfer, which was proven by photoelectrochemical tests and TRPL spectroscopy. Quenching experiments, EPR and photoelectrochemical measurement indicated that oxygen vacancies facilitated charge transfer, to increase the activation of molecular oxygen and subsequent ∙O2- and 1O2 production for pollutant degradation. This study provides an in-depth explanation of the role of oxygen vacancies in tetracycline adsorption, surface complex due to the intermediate state in adsorption and molecular oxygen activation, as well as a reference for antibiotic removal via adsorption coupling degradation.

A Stable Zn-MOF for Photocatalytic Csp3–H Oxidation: Vinyl Double Bonds Boosting Electron Transfer and Enhanced Oxygen Activation

Molecular oxygen activation has always been a difficult issue and challenge in heterogeneous photocatalytic aerobic oxidations due to the kinetically persistent or spin-forbidden nature of O2. In this work, a highly delocalized interpenetrated 3D MOF photocatalyst with high stability, Zn-TACPA (H3TACPA = tris(3-carboxybiphenyl)amine), based on vinyl-functionalized triphenylamine and bipyridine ligands has been fabricated and employed as a reactive oxygen species (ROS) generator to catalyze the photooxidative CDC/aromatization tandem reaction of glycine esters and styrenes. In comparison to a similar triphenylamine MOF (Zn-TCA), DFT calculations and extensive control experiments reveal that the introduction of functional vinyl double bonds not only optimizes the visible-light absorption and photoredox potential of triphenylamine ligand to powerfully activate O2 via a single-electron-transfer process but also improves the conjugation degree, charge-carrier separation, and migration efficiency of the MOF semiconductor for rapid O2 activation. Such an oxygen activation ability endows Zn-TACPA with a catalytic yield of up to 91%, 2.6 times higher than that of Zn-TCA. Furthermore, the crucial intermediates and activation processes were also properly captured and monitored by a series of experiments including ESI-MS, ESR, IR, and fluorescence analyses to better understand the possible catalytic mechanisms.

Boosting the photocatalytic activation of molecular oxygen and photodegradation of tetracycline: The role of interfacial synergistic effect of cocatalyst and dopants

Utilizing reactive oxygen species (ROS), which are generated by the activation of molecular oxygen (O2) in oxidation reaction, is a promising method for pollutant degradation. However, it is limited by the commonly low efficiency of O2 activation and carrier separation. Herein, as a model system, Ag cocatalyst and Cl doping modified g-C3N4 (Ag/Cl-CN) was constructed to improve the ability of O2 activation. Results showed that Ag/Cl-CN could effectively convert more O2 into ROS than pristine g-C3N4 (CN), and individually decorated CN (Ag-CN and Cl-CN). A series of experiments and DFT calculations revealed that the deposition of Ag could promote charge separation resulting in more charges accumulated around O2 and the introduction of Cl led to a stronger adsorption capacity for O2. Therefore, due to the synergistic effect of Ag cocatalyst and Cl dopant, Ag/Cl-CN generated higher concentrations of O2− and displayed much better activity for photocatalytic degradation of tetracycline (TC) than CN, Ag-CN and Cl-CN.

Roles of Oxygen Species in Low-Temperature Catalytic o-Xylene Oxidation on MOF-Derived Bouquetlike CeO2

To realize efficient low-temperature catalytic o-xylene oxidation, MOF-derived CeO2-X catalysts were prepared via the pyrolysis of MOF precursors with different ratios of cerium nitrate to trimesic acid. Among the synthesized catalysts, the bouquet like CeO2-1 exhibited the best activity with T50 and T90 of 156 and 198 °C and the lowest activation energy of 60.67 kJ·mol-1 (WHSV= 48 000 mL·g-1·h-1, o-xylene concentration = 500 ppm). o-Xylene was completely mineralized, and no change in conversion efficiency or CO2 yield was found at 5 vol % H2O for over 50 h. The rich active oxygen species (XPS: Osur/Olatt = 0.69) and abundant oxygen vacancies (Raman: ID/IF2g = 0.036) of CeO2-1 made crucial contribution to its superior catalytic activity. The O2-TPD and H2-TPR results confirmed that CeO2-1 had more surface active oxygen and better mobility of bulk oxygen. Moreover, the reaction routes under different atmospheres were probed through in situ DRIFTS, in which oxygen vacancy played a key role in promoting the adsorption and activation of molecular oxygen and facilitating the migration of the bulk lattice oxygen.

Back Cover: Chromophore‐Inspired Design of Pyridinium‐Based Metal–Organic Polymers for Dual Photoredox Catalysis (Angew. Chem. Int. Ed. 37/2022)

A universal dual photoredox catalysis platform based on metal–organic polymers synergistically constructed with triphenylpyrylium mimic ligands and reductive metal ions is reported by Yunhe Jin, Chunying Duan et al. in their Research Article (DOI: 10.1002/anie.202204918). This novel strategy enables integration of photoinduced electron transfer and ligand-to-metal charge transfer events, and spatial and kinetic confinement effects of structurally confined pores for enhanced efficiency in photocatalysis of various organic couplings and molecular oxygen activation.

An Electrochemical Strategy for Simultaneous Heavy Metal Complexes Wastewater Treatment and Resource Recovery.

Heavy metals chelated with coexisting organic ligands in wastewater impose severe risks to public health and the ambient ecosystem but are also valuable metal resources. For sustainable development goals, the treatment of heavy metal complexes wastewater requires simultaneous metal-organic bond destruction and metal resource recovery. In this study, we demonstrated that a neutral pH electro-Fenton (EF) system, which was composed of an iron anode, carbon cloth cathode, and sodium tetrapolyphosphate electrolyte (Na6TPP), could induce a successive single-electron activation pathway of molecular oxygen due to the formation of Fe(II)-TPP complexes. The boosted •OH generation in the Na6TPP-EF process could decomplex 99.9% of copper ethylene diamine tetraacetate within 8 h; meanwhile, the released Cu ions were in situ deposited on the carbon cloth cathode in the form of Cu nanoparticles with a high energy efficiency of 2.45 g kWh-1. Impressively, the recovered Cu nanoparticles were of purity over 95.0%. More importantly, this neutral EF strategy could realize the simultaneous removal of Cu, Ni, and Cr complexes from real electroplating effluents. This study provides a promising neutral EF system for simultaneous heavy metal complexes wastewater treatment and resource recovery and sheds light on the importance of molecular oxygen activation in the field of pollutant control.

Interstitial Atomic Bi Charge‐Alternating Processor Boosts Twofold Molecular Oxygen Activation Enabling Rapid Catalytic Oxidation Reactions at Room Temperature

AbstractMolecular O2 activation on metallic oxide‐based catalysts surfaces is pivotal for catalytic oxidation reactions but highly depends on the O2 activation pathways or mechanisms. Thus, comprehensively understanding the mechanism of efficient O2 activation is conducive to extending the fundamental principles for O2 activation theories and designing novel catalysts for catalytic oxidation reactions. In this study, it is declared that the interstitial atomic Bi (IA Bi) anchored in the lattice interstice of MnO2 (Bi/MnO2) is capable of triggering an alternative twofold O2 activation boosting the catalytic oxidation reactions at room temperature. Explicitly, the IA Bi facilely induces the local lattice distortion reconstructing the local charge landscape, thus weakening the O2 dissociation energy barrier by elongating the OO bond length. And, the charge‐alternating process engineered by the IA Bi drives the alternative twofold O2 activation of the adjacent lattice oxygen and adsorbs dangling oxygen assisted by the consecutive O2 replenishment. Conclusively, this study not only declares the role of IA Bi in driving the charge‐alternating process during the twofold O2 activation but also extends the fundamental principles toward O2 activation mechanisms for catalytic oxidation reactions via atomic makeup engineering.

Chromophore‐Inspired Design of Pyridinium‐Based Metal–Organic Polymers for Dual Photoredox Catalysis

Abstract2,4,6‐Triphenylpyrylium (TPT+) functions as a classic organic photocatalyst and exhibits a noteworthy absorption in the visible range, strongly oxidizing excited states, and a somewhat unstable structure. Inspired by the nuclear chromophore and dual catalysis strategy, herein, we report a universal photoredox platform constructed byTPT+‐mimic bridging ligands and reductive metal ions on the basis of metal–organic supramolecular systems for various organic couplings and molecular oxygen activation under visible‐light irradiation. Significant photoinduced electron transfer and ligand‐to‐metal charge‐transfer events are both integrated and regulated by the spatial and kinetic confinement effects of the structurally confined microenvironments, effectively improving the efficiency of electron transfer and radical–radical coupling processes in photocatalysis. This package deal provides a promising way for the design of novel photocatalysts and the development of versatile and sustainable synthetic chemistry.

Chromophore-Inspired Design of Pyridinium-Based Metal-Organic Polymers for Dual Photoredox Catalysis.

2,4,6-Triphenylpyrylium (TPT+ ) functions as a classic organic photocatalyst and exhibits a noteworthy absorption in the visible range, strongly oxidizing excited states, and a somewhat unstable structure. Inspired by the nuclear chromophore and dual catalysis strategy, herein, we report a universal photoredox platform constructed by TPT+ -mimic bridging ligands and reductive metal ions on the basis of metal-organic supramolecular systems for various organic couplings and molecular oxygen activation under visible-light irradiation. Significant photoinduced electron transfer and ligand-to-metal charge-transfer events are both integrated and regulated by the spatial and kinetic confinement effects of the structurally confined microenvironments, effectively improving the efficiency of electron transfer and radical-radical coupling processes in photocatalysis. This package deal provides a promising way for the design of novel photocatalysts and the development of versatile and sustainable synthetic chemistry.

Universal strategy engineering grain boundaries for catalytic oxidative desulfurization

The low-coordinated atoms such as edges, single atoms and vacancies have been widely determined as reactive sites for catalytic oxidative desulfurization. However, the grain boundaries (GB) as a favorable atomic configuration has been ignored. In this work, a universal strategy is proposed to engineer grain boundaries into oxides via facile two-step growth. Take the W18O49 nanowires as an example, the engineered GB can work as reactive sites to build stronger interfacial molecular interactions with dibenzothiophene (DBT) due to the low-coordinated W atoms with local electron-rich state, promoting the surface adsorption and activation performance towards DBT. Moreover, the molecular oxygen activation capacity is improved by GB to yield more superoxide radical relative to W18O49. Benefiting from these features, the GB-W18O49 deliver a greatly improved catalytic oxidative desulfurization behavior relative to W18O49 nanowires, in which 97.7% DBT can be removed by GB-W18O49 in 5 h but only 40.4% of W18O49 nanowires.

Manganese porphyrin-mediated aerobic epoxidation of propylene with isoprene: A new strategy for simultaneously preparing propylene epoxide and isoprene monoxide

The direct epoxidation of propylene by O2 is a significant and challenging topic. The key factor for this homogeneous aerobic epoxidation is the activation of molecular oxygen under mild conditions. In this work, the aerobic epoxidation of propylene catalyzed by manganese porphyrins was achieved in the presence of isoprene. Isoprene contains an allyl methyl group, and the α-H can be easily removed to achieve the activation of molecular oxygen. The conversion of propylene was 38% and the selectivity toward propylene oxide (PO) was up to 87%. The role of isoprene was demonstrated, and a plausible mechanism was proposed. The protocol reported herein is expected to provide a strategy for the simultaneous preparation of propylene oxide and isoprene monoxide.

Low‐Voltage‐Driven Electrochemical Aerobic Oxygenation with Flavin Catalysis: Chemoselective Synthesis of Sulfoxides from Sulfides

AbstractThe chemoselective electrochemical oxygenation of sulfides to sulfoxides is performed using a biomimetic flavin catalyst that enables the activation of molecular oxygen under a low cathode potential. Diverse functional groups, including alcohols, ketones, aldehydes, cyclopropane, carboxylic acids, pyridine, alkenes, and alkynes, are well tolerated under low‐voltage electrolytic conditions.magnified image

Solvent-Induced Isomeric Cu13 Nanoclusters: Chlorine to Copper Charge Transfer Boosting Molecular Oxygen Activation in Sulfide Selective Oxidation

Isomers with minimal structural dissimilarities are promising research objects to obtain a comprehensive understanding of structure-property relationships; however, comparability of isomeric structures is a prerequisite. Herein, two quasi-structurally isomeric 13-nuclei copper nanoclusters (Cu NCs) (Cu13a and Cu13b) containing highly similar Cu13 kernels and different arrangements of peripheral ligands were obtained using a solvent-induced strategy. The exotic chloride ion is shown to play a prominent role in inducing the selective formation of two quasi-isomers, where the comparative study to establish a structure-property relationship was realized. Due to the charge transition from chlorine to the copper core (X(Cl)M(Cu)CT), the molecular oxygen activation of Cu13a showed higher singlet oxygen (1O2) and lower superoxide radical (O2•-) yields compared to those of Cu13b, which gives it better catalytic selectivity for the 1O2 involved selective oxidation of sulfides. The present work not only offers a controllable strategy for the rational design and synthesis of quasi-structurally isomeric Cu NCs but also provides a pathway to boost catalytic selectivity by a halogen to metal core charge transition.

Electrocatalytic oxidation of toluene into benzaldehyde based on molecular oxygen activation over oxygen vacancy of heteropoly acid

Benzaldehyde is much easier to be oxidized with respect to toluene, making the selective oxidation of toluene to benzaldehyde extremely challenging. Herein, a series of heteropoly acid catalysts with different ratios of molybdenum and vanadium supported on carbon paper (CP) were synthesized. The oxygen vacancy concentration and dispersion of heteropoly acid on CP can be changed by regulating the ratio of molybdenum and vanadium. Due to the suitable oxygen vacancy concentration and most uniform dispersion on CP, HPMoV2 has the highest electrocatalytic oxidation performance, showing the benzaldehyde selectivity of 83.5% at the toluene conversion of 83.4%. In-situ Raman spectroscopy proved that toluene was initially activated into benzyl cation and further oxidized by active oxygen species (O22-ads, O2-ads) to form benzaldehyde. The active oxygen species generated by electro-activation of molecular oxygen adsorbed on oxygen vacancies of heteropoly acid, mainly contribute to the selective oxidization of toluene into benzaldehyde. This work develops a new electrochemical strategy to achieve highly selective conversion of toluene into benzaldehyde with molecular oxygen under mild conditions.