High-valent Manganese Research Articles

Enhanced peroxymonosulfate activation by MnOOH/CoOOH composites for efficient phenol degradation: Mechanistic insights and practical implications

The strong electronic interactions between metal oxide components are crucial for the activation of peroxymonosulfate (PMS) in pollutant degradation. In this study, an innovative MnOOH/CoOOH composite material (labeled as B-MCo-0.1) was synthesized through mesoscale chemical coupling, serving as an efficient PMS activator for phenol degradation. Experimental findings suggest that CoOOH nanosheets incorporated on MnOOH surface prevent CoOOH aggregation, increase specific surface area, and enhance the synergistic interaction between components, thereby improving activation and degradation efficiency. Under optimal conditions, a 50 mL phenol solution (25 mg/L) can achieve 100 % degradation within 10 minutes. XPS analysis reveals that the robust electronic interaction between CoOOH and MnOOH facilitates PMS activation, generating reactive oxygen species (ROS) that effectively degrade phenol through both non-radical and radical pathways. Experiments, including quenching tests, electrochemical analysis, electron paramagnetic resonance (EPR) measurements, and sulfoxide method experiments for identifying high-valent metal oxides confirm that singlet oxygen (1O2) and superoxide anion (·O2−) play major roles in this process. Additionally, high-valent manganese oxides and electron transfer complexes on the catalyst surface, generated under strong electronic interactions, also contribute significantly to phenol degradation. By exploring the pivotal role of robust electronic interactions in activating PMS, this study extends the potential applications of MnOOH-based materials in environmental remediation.

Overlooked Complexation and Competition Effects of Phenolic Contaminants in a Mn(II)/Nitrilotriacetic Acid/Peroxymonosulfate System: Inhibited Generation of Primary and Secondary High-Valent Manganese Species.

Organic contaminants with lower Hammett constants are typically more prone to being attacked by reactive oxygen species (ROS) in advanced oxidation processes (AOPs). However, the interactions of an organic contaminant with catalytic centers and participating ROS are complex and lack an in-depth understanding. In this work, we observed an abnormal phenomenon in AOPs that the degradation of electron-rich phenolics, such as 4-methoxyphenol, acetaminophen, and 4-presol, was unexpectedly slower than electron-deficient phenolics in a Mn(II)/nitrilotriacetic acid/peroxymonosulfate (Mn(II)/NTA/PMS) system. The established quantitative structure-activity relationship revealed a volcano-type dependence of the degradation rates on the Hammett constants of pollutants. Leveraging substantial analytical techniques and modeling analysis, we concluded that the electron-rich phenolics would inhibit the generation of both primary (Mn(III)NTA) and secondary (Mn(V)NTA) high-valent manganese species through complexation and competition effects. Specifically, the electron-rich phenolics would form a hydrogen bond with Mn(II)/NTA/PMS through outer-sphere interactions, thereby reducing the electrophilic reactivity of PMS to accept the electron transfer from Mn(II)NTA, and slowing down the generation of reactive Mn(III)NTA. Furthermore, the generated Mn(III)NTA is more inclined to react with electron-rich phenolics than PMS due to their higher reaction rate constants (8314 ± 440, 6372 ± 146, and 6919 ± 31 M-1 s-1 for 4-methoxyphenol, acetaminophen, and 4-presol, respectively, as compared with 671 M-1 s-1 for PMS). Consequently, the two-stage inhibition impeded the generation of Mn(V)NTA. In contrast, the complexation and competition effects are insignificant for electron-deficient phenolics, leading to declined reaction rates when the Hammett constants of pollutants increase. For practical applications, such complexation and competition effects would cause the degradation of electron-rich phenolics to be more susceptible to water matrixes, whereas the degradation of electron-deficient phenolics remains largely unaffected. Overall, this study elucidated the intricate interaction mechanisms between contaminants and reactive metal species at both the electronic and kinetic levels, further illuminating their implications for practical treatment.

Structure and molecular-level transformation for oxidation of effluent organic matters by manganese oxides

As important organic components in water environments, effluent organic matters (EfOMs) from wastewater treatment plants are widely present in Mn-rich environments or engineered treatment systems. The redox interaction between manganese oxides (MnOx) and EfOMs can lead to their structural changes, which are crucial for ensuring the safety of water environments. Herein, the reactivities of MnOx with EfOMs were evaluated, and it was found that MnOx with high specific surface area, active high-valent manganese content and lattice oxygen content (i.e., amorphous MnO2) possessed stronger oxidizing ability towards EfOMs. Accompanying by EfOMs oxidation, Mn(IV) and Mn(III) were reduced into Mn(II), with Mn(III) as the significant active species. Through molecular-level transformation analysis by ultrahigh mass spectrometry (FT-ICR MS), the highly reactive compounds in EfOMs were clearly determined to be that with more aromatic and unsaturated structures, especially lignin-like compounds (the highest content in EfOMs (over 60 %)). EfOMs were oxidized by amorphous MnO2 into products with lower humification index (0.60 vs. 0.46), smaller apparent molecular weight (386.94 Da vs. 368.68 Da), and higher biodegradability (BOD5/COD: 0.12 vs. 0.78). This finding suggested that redox reactions between MnOx and EfOMs might alter their abiotic and biotic behaviors in receiving water environments.

A Combination of Biocatalysis and Fenton-Like Reaction Induced OH• Burst for Cascade Amplification of Cancer Chemodynamic Therapy.

Chemodynamic therapy (CDT) is a novel antitumor strategy that employs Fenton or Fenton-like reactions to generate highly toxic hydroxyl radical (OH•) from hydrogen peroxide (H2O2) for inducing tumor cell death. However, the antitumor efficacy of the CDT strategy is harshly limited by the redox homeostasis of tumor cells; especially the OH • is easily scavenged by glutathione (GSH) and the intracellular H2O2 level is insufficient in the tumor cells. Herein, we propose the Mn2+-menadione (also known as vitamin K3, MK3) cascade biocatalysis strategy to disrupt the redox homeostasis of tumor cells and induce a OH• storm, resulting in enhanced CDT effect. A nanoliposome encapsulating Mn-MK3 (Mn-MK3@LP) was prepared for the treatment of hepatic tumors in this study. After Mn-MK3@LPs were taken up by tumor cells, menadione could facilitate the production of intracellular H2O2 via redox cycling, and further the cytotoxic OH • burst was induced by Mn2+-mediated Fenton-like reaction. Moreover, high-valent manganese ions were reduced by GSH and the depletion of GSH further disrupted the redox homeostasis of tumor cells, thus achieving synergistically enhanced CDT. Overall, both cellular and animal experiments confirmed that the Mn-MK3@LP cascade biocatalysis nanoliposome exhibited excellent biosafety and tumor suppression efficacy. This study may provide deep insights for developing novel CDT-based strategies for tumor therapy.

Optimizing the CeO2-MnO2 interface via H2O2 etching for surface lattice oxygen activation in the plasma catalytic degradation of trimethylamine

Trimethylamine (TMA) is a nitrogen-containing malodorous gas that is toxic and hazardous to humans. Plasma catalysis is a promising technique for removing low-concentration malodorous gases. CeO2/MnO2 nanowires with different Ce–Mn contact interfaces prepared by impregnation, physical mixing, and H2O2 etching were investigated for TMA degradation in a plasma catalytic system. The CMO-H sample prepared by H2O2 etching achieved a removal efficiency of 100% at 98 J/L, demonstrating the highest activity. Characterization revealed that H2O2 etching led to the uniform formation of CeO2 nanoparticles on MnO2, promoting the transfer of electrons between Ce and Mn species. Surface lattice oxygen and high-valent manganese were confirmed to be the main active species, consistent with the Mars van Krevelen mechanism. Density functional theory calculations confirmed that the CMO-H sample exhibited the lowest oxygen vacancy formation energy. In situ plasma diffuse reflection infrared transform spectroscopy analysis and gas chromatography-mass spectrometry results showed the possible degradation pathway of TMA. In summary, the H2O2 etching process optimized CeO2-MnO2 interactions and improved the utilization of lattice oxygen active sites, enhancing the catalytic degradation of TMA and providing new insights into the design of an efficient plasma catalytic system for environmental remediation.

A mechanistic study of chiral manganese porphyrin-catalyzed enantioselective C-H hydroxylation reaction.

We employed density functional theory (DFT) calculations to elucidate the mechanism and origin of enantioselectivity in the C-H hydroxylation reaction catalyzed by a chiral manganese porphyrin complex. Our study reveals that the chiral manganese porphyrin forms a two-point hydrogen bonding interaction with the substrate. Specifically, the hydrogen atom abstraction of the methylene pro-(S) C-H bond at the heterocyclic C-3 position is 1.9 kcal mol-1 favored over the hydrogen atom abstraction of the pro-(R) C-H bond. This preferential reactivity results in the predominant formation of (S)-hydroxylated products. Our DFT calculations are consistent with the experimental findings of high enantioselectivity in the chiral manganese porphyrin catalyzed C(sp3)-H hydroxylation of lactam derivatives. The observed enantioselectivity arises from the formation of two-point hydrogen bonding between lactam derivatives and manganese porphyrin catalysts. Moreover, our computations indicate varying degrees of substrate distortion upon attack by high-valent manganese oxygen complexes at different hydrogen atoms.

The oxidation behavior of MnO2 on the surface of a shale vanadium ore

As a typical oxidative leaching aid in the experimental study of vanadium extraction, MnO2 has a strong destructive effect on the lattice of vanadium-containing minerals. Therefore, the effect of manganese dioxide on vanadium leaching was studied by leaching test of shale vanadium ore. Firstly, the phase change, microstructure and possible structure of the compounds during the condition test were studied by EPMA, FT-IR and SEM-EPS. Then the effect of MnO2 on the leaching rate was studied by kinetics. The results show that under the action of manganese dioxide, the leaching control type is changed from chemical reaction control to mixed control type, and the activation energy is greatly reduced. Secondly, the adsorption of shale vanadium ore by manganese dioxide was characterized, and the density of states, the differential charge density under the action of MnO2 and the dissolution behavior of MnO2 on vanadium in minerals during leaching were studied. Based on the simulation results, it is found that there is a molecular orbital interaction between manganese ions and oxygen and hydrogen on the surface of minerals, which will seriously destroy the lattice of vanadium-containing minerals. The strong oxidation of manganese ions will destroy the structure and stability of the whole tetrahedron and accelerate the leaching trend. Under the action of high-valent manganese ions, Al (S7) -O (S1) bond breaks, Al (S7-O) bond breaks, and vanadium is more easily dissociated from minerals. In this paper, the leaching of vanadium from manganese dioxide was studied by the combination of leaching test, kinetics and quantum chemistry. Through the analysis of kinetics, density of states and charge distribution, the leaching process which could not be characterized by the test was analyzed in detail. It also provides a feasible reference for future research.

Selective abatement of electron-rich organic contaminants by trace complexed Mn(II)-catalyzed periodate via high-valent manganese–oxo species

Mn(II) is among the most efficient catalysts for the periodate (PI)-based oxidation process. In-situ formed colloidal MnO2 simultaneously serves as the catalyst and oxidant during the degradation of organic contaminants by PI. Here, it is revealed that the complexation of Mn(II) by ethylene diamine tetraacetic acid (EDTA) further enhances the performance of PI-based oxidation in the selective degradation of organic contaminants. As evidenced by methyl phenyl sulfoxide probing, 18O-isotope labeling, and mass spectroscopy, EDTA complexation modulates the reaction pathway between Mn(II) and PI, triggering the generation of high-valent manganese–oxo (MnV–oxo) as the dominant reactive species. PI mediates the single-electron oxidation of Mn(II) to Mn(III), which is stabilized by EDTA complexation and then further oxidized by PI via the oxygen-atom transfer step, ultimately producing the MnV–oxo species. Ligands analogous to EDTA, namely, [S,S]-ethylenediaminedisuccinic acid and L-glutamic acid N,N-diacetic acid, also enhances the Mn(II)/PI process and favors MnV–oxo as the dominant species. This study demonstrates that functional ligands can tune the efficiency and reaction pathways of Mn(II)-catalyzed peroxide and peroxyacid-based oxidation processes.

Degradation of dimethyl phthalate by morphology controlled β-MnO2 activated peroxymonosulfate: The overlooked roles of high-valent manganese species

Activated peroxymonosulfate (PMS) processes have emerged as an efficient advanced oxidation process to eliminate refractory organic pollutants in water. This study synthesized a novel spherical manganese oxide catalyst (0.4KBr-β-MnO2) via a simple KBr-guided approach to activate PMS for degrading dimethyl phthalate (DMP). The 0.4KBr-β-MnO2/PMS system enhanced DMP degradation under different water quality conditions, exhibiting an ultrahigh and stable catalytic activity, outperforming equivalent quantities of pristine β-MnO2 by 8.5 times. Mn(V) was the dominant reactive species that was revealed by the generation of methyl phenyl sulfone from methyl phenyl sulfoxide oxidation. The selectivity of Mn(V) was demonstrated by the negligible inhibitory effects of Inorganic anions. Theoretical calculations confirmed that Mn (V) was more prone to attack the CO bond of the side chain of DMP. This study revealed the indispensable roles of high-valent manganese species in DMP degradation by the 0.4KBr-β-MnO2/PMS system. The findings could provide insight into effective PMS activation by Mn-based catalysts to efficiently degrade pollutants in water via the high-valent manganese species.

Unveiling different antibiotic degradation mechanisms on dual reaction center catalysts with nitrogen vacancies via peroxymonosulfate activation

Metal-nitrogen-site catalysts are widely recognized as effective heterogeneous catalysts in peroxymonosulfate (PMS)-based advanced oxidation processes. However, the selective oxidation mechanism for organic pollutants is still contradictory. In this work, manganese-nitrogen active centers and tunable nitrogen vacancies were synchronously constructed on graphitic carbon nitride (LMCN) through l-cysteine-assisted thermal polymerization to reveal different antibiotic degradation mechanisms. Benefiting from the synergism of manganese-nitrogen bond and nitrogen vacancies, the LMCN catalyst exhibited excellent catalytic activity for the degradation of tetracycline (TC) and sulfamethoxazole (SMX) antibiotics with first-order kinetic rate constants of 0.136 min−1 and 0.047 min−1, which were higher than those of other catalysts. Electron transfer dominated TC degradation at low redox potentials, while electron transfer and high-valent manganese (Mn (V)) were responsible for SMX degradation at high redox potentials. Further experimental studies unveiled that the pivotal role of nitrogen vacancies is to promote electron transfer pathway and Mn(V) generation, while nitrogen-coordinated manganese as the primary catalytic active site determines Mn(V) generation. In addition, the antibiotic degradation pathways were proposed and the toxicity of byproducts was analyzed. This work provides an inspiring idea for the controlled generation of reactive oxygen species by targeted activation of PMS.

A Manganese Compound I Model with a High Reactivity in the Oxidation of Organic Substrates and Water.

A high-valent manganese(IV)-hydroxo porphyrin π-cation radical complex, [Mn(IV)(OH)(Porp+•)(X)]+, was synthesized and characterized spectroscopically. The Mn porphyrin intermediate was highly reactive in alkane hydroxylation and oxygen atom transfer reactions. More importantly, the Mn porphyrin intermediate reacted with water at a fast rate, resulting in the dioxygen evolution. To the best of our knowledge, we report the first manganese Cpd I model compound bearing a porphyrin π-cation radical ligand with a high reactivity in oxidation reactions, including water oxidation.

Co-Precipitated Mn0.15Ce0.85O2−δ Catalysts for NO Oxidation: Manganese Precursors and Mn-Ce Interactions

Two Mn0.15Ce0.85O2−δ mixed oxides were synthesized by a co-precipitation method using Mn(NO3)2 and KMnO4 as the manganese precursors, respectively. Structural analyses by X-ray powder diffraction and Raman spectroscopy reveal the formation of MnOx-CeO2 solid solutions. The Mn0.15Ce0.85O2−δ catalyst prepared from the high-valent manganese precursor exhibits higher activity for the catalytic oxidation of NO. The advantage of KMnO4 is related to the improved redox property of the catalyst as supported by H2 temperature-programmed reduction (TPR) and O2 temperature-programmed desorption (TPD). The Mn-Ce interactions create more Mn4+, Ce3+ and oxygen vacancies on the KMnO4-synthesized mixed oxides based on the Raman and X-ray photoelectron spectra (XPS).

Catalytic Behavior of Ag-Mn Catalyst for Efficient Toluene Removal at Low Temperature: Effect of Redox Property

Ag-Mn bimetallic catalysts were prepared by liquid-phase redox method and discussed their synergistic effect on the catalytic oxidation of toluene. The activity order of the catalysts was: Ag-Mn > Mn > Ag-Mn-R > Mn-R. The addition of Ag caused some K+ to be substituted over Ag-Mn, which resulted in the collapse of the structure, and led to more lattice defects and increased the active species. Furthermore, the Ag-Mn catalyst contained a large amount of Mn4+ and Olatt species, the best low-temperature reducibility and the lowest oxygen desorption temperature. After the reduction treatment, the high-valent manganese ions decreased, and the lattice oxygen concentration was greatly reduced. Besides, the high concentration of high valence manganese, easily released lattice oxygen and oxidized silver of Ag-Mn could contribute to the superior catalytic performance. The mechanism followed by toluene → benzoate → benzoquinone → manganese carbonate → CO2 + H2O.

Regulation of A-site cations in AMn2Ox spinel catalysts on the deep oxidation of light alkanes VOCs

Light alkane VOCs are currently the most difficult VOCs to deal with in the petroleum and coal chemical industries due to their short carbon chains and stable molecular structures. On account of the metal components of spinel are diverse and the structure can be adjusted. Thus, a series of A-site cations substituted AMn2Ox (A = Co, Cu, Ni, Zn, Ce) spinel catalysts were prepared and the impacts of A-site cations on the oxidation of alkane were revealed. It was found that A-site metal ions made a big difference in the low-temperature reduction, lattice oxygen activity, high-valent manganese ion content, and oxygen vacancies with NiMn2O4 had the highest catalytic activity with a conversion of 90 % at 232 °C. In addition, in-situ DRIFTs were performed to investigate the underlying oxidation mechanisms for propane oxidation. We found that propane is firstly dehydrogenated by adsorption on the active site and then oxidized to carboxylates and carbonates, which are further converted to CO2 and H2O. Moreover, the catalyst also showed good stability and robust resistance of H2O and SO2. The excellent activity exhibited by Ni-Mn-based spinels may shed light on the development of efficient catalysts for light alkanes catalytic oxidation.

Aliphatic and Aromatic C–H Bond Oxidation by High-Valent Manganese(IV)-Hydroxo Species

The strong C-H bond activation of hydrocarbons is a difficult reaction in environmental and biological chemistry. Herein, a high-valent manganese(IV)-hydroxo complex, [MnIV(CHDAP-O)(OH)]2+ (2), was synthesized and characterized by various physicochemical measurements, such as ultraviolet-visible (UV-vis), electrospray ionization-mass spectrometry (ESI-MS), electron paramagnetic resonance (EPR), and helium-tagging infrared photodissociation (IRPD) methods. The one-electron reduction potential (Ered) of 2 was determined to be 0.93 V vs SCE by redox titration. 2 is formed via a transient green species assigned to a manganese(IV)-bis(hydroxo) complex, [MnIV(CHDAP)(OH)2]2+ (2'), which performs intramolecular aliphatic C-H bond activation. The kinetic isotope effect (KIE) value of 4.8 in the intramolecular oxidation was observed, which indicates that the C-H bond activation occurs via rate-determining hydrogen atom abstraction. Further, complex 2 can activate the C-H bonds of aromatic compounds, anthracene and its derivatives, under mild conditions. The KIE value of 1.0 was obtained in the oxidation of anthracene. The rate constant (ket) of electron transfer (ET) from N,N'-dimethylaniline derivatives to 2 is fitted by Marcus theory of electron transfer to afford the reorganization energy of ET (λ = 1.59 eV). The driving force dependence of log ket for oxidation of anthracene derivatives by 2 is well evaluated by Marcus theory of electron transfer. Detailed kinetic studies, including the KIE value and Marcus theory of outer-sphere electron transfer, imply that the mechanism of aromatic C-H bond hydroxylation by 2 proceeds via the rate-determining electron-transfer pathway.

In situ anchoring strategy to enhance dual nonradical degradation of sulfamethoxazole with high loading manganese doped carbon nitride.

A low-cost catalyst with high metal loading and unique catalytic activities is highly desired for peroxymonosulfate (PMS) activation in environmental remediation. Herein, in situ anchoring strategy using 1,10-phenanthroline is reported to construct manganese doped carbon nitride (PMCN) with 8.2wt% manganese loading and dramatically enhanced PMS adsorption and sulfamethoxazole (SMX) removal efficiency. Our study revealed that the PMCN/PMS system readily reacted with contaminants with electron-rich groups, where complete degradation of sulfamethoxazole (SMX) was achieved within 60min. Combining quenching experiments, EPR tests, and electrochemical analysis, we proposed a dual nonradical pathway dominated by high-valent manganese oxygen species (Mn(V)=O) and electron transfer. Systematic investigation elucidated that the introduction of 1,10-phenanthroline constructed denser catalyst active sites, and identified the manganese center and pyridine nitrogen as the active sites for PMS activation. Furthermore, PMCN exhibited excellent pH anti-interference ability and good reusability, achieving more than 90% SMX degradation efficiency after four cycles. This study provides new insights into the regulation of Mn-N active sites and promotes the mechanistic understanding of the synergistic effect of manganese and pyridine nitrogen in PMS activation.

Single atom Mn anchored on N-doped porous carbon derived from spirulina for catalyzed peroxymonosulfate to degradation of emerging organic pollutants

Highly efficient single atom catalysts are critical to substantially promote for peroxymonosulfate (PMS) activation to organic pollutant degradation, but it remains a challenge at present. Herein, single atom Mn anchored on N-doped porous carbon (SA-Mn-NSC) was synthesized by ball milling of Mn-doped carbon nitride and spirulina biochar to dominantly activate PMS. The precursor of carbon nitride and spirulina possessed a strong coordinating capability for Mn(II), facilitating the formation of highly dispersed nitrogen-coordinated Mn sites (Mn-N4). The SA-Mn-NSC catalyst exhibited high activity and stability in the heterogeneous activation of PMS to degrade a wide range of pollutants within 10 min, showing an outstanding degradation rate constant of 0.31 min−1 in enrofloxacin (ENR) degradation. The high surface density of Mn-N4 sites and abundant interconnected meso–macro pores were highly favorable for activating PMS to produce 1O2 and high-valent manganese (Mn(IV)) for pollutant degradation. This work offers a new pathway of using a low-cost and easily accessible single-atom catalysts (SACs) and could inspire more catalytic oxidation strategies.

Modular Difunctionalization of Unactivated Alkenes through Bio-Inspired Radical Ligand Transfer Catalysis.

Development of visible light-mediated atom transfer radical addition of haloalkanes onto unsaturated hydrocarbons has seen rapid growth in recent years. However, due to its radical chain propagation mechanism, diverse functionality other than the pre-existing (pseudo-)halide on the alkyl halide source cannot be incorporated into target molecules in a one-step, economic fashion. Inspired by the prominent reactivities shown by cytochrome P450 hydroxylase and non-heme iron-dependent oxygenases, we herein report the first modular, dual catalytic difunctionalization of unactivated alkenes via manganese-catalyzed radical ligand transfer (RLT). This RLT elementary step involves a coordinated nucleophile rebounding to a carbon-centered radical to form a new C-X bond in analogy to the radical rebound step in metalloenzymes. The protocol leverages the synergetic cooperation of both a photocatalyst and earth-abundant manganese complex to deliver two radical species in succession to minimally functionalized alkenes, enabling modular diversification of the radical intermediate by a high-valent manganese species capable of delivering various external nucleophiles. A broad scope (97 examples, including drugs/natural product motifs), mild conditions, and excellent chemoselectivity were shown for a variety of substrates and fluoroalkyl fragments. Mechanistic and kinetics studies provide insights into the radical nature of the dual catalytic transformation and support radical ligand transfer (RLT) as a new strategy to deliver diverse functionality selectively to carbon-centered radicals.

Insight into the oxidation of phenolic pollutants by enhanced permanganate with biochar: The role of high-valent manganese intermediate species

This work demonstrated that the oxidation of phenolic pollutants by permanganate (KMnO4) was effectively enhanced by a commercial biochar. Detailed characterization data indicated that the biochar contains porous structures, amounts of defective sites and abundant redox-active groups. In the presence of biochar, the degradation efficiency of 4-nitrophenol by KMnO4 surged from 5% to 92% in 180 min, up to 37.8% of total organic carbon (TOC) was removed. Meanwhile, acute toxicity of 4-nitrophenol was greatly reduced. Through analyzing oxidation products of triclosan (TCS) and using methyl phenyl sulfoxide (PMSO) as a chemical probe, high-valent Mn intermediates (i.e. Mn(VI)/Mn(V)) were proved to be the dominant oxidant in the KMnO4/biochar system. Quantitative structure-activity relationships (QSARs) were established between oxidation rate constants of various substituted phenols and classical descriptor variables (i.e., Hammett constant σ+). KMnO4/biochar was found to be less selective to the substituent variation of phenolic compounds compared with O3, K2FeO4, ClO2 and persulfate/carbon nanotube (PDS/CNT). This work provided a novel catalytic oxidation technology for eliminating phenolic compounds, and improved insights into the mechanistic study of the KMnO4-based oxidation process.

Effects of deep eutectic solvent on Cu-Mn-C-O composite catalysts: Surface species, physical and chemical properties in methane combustion

A series of Cu-Mn-C-O composite catalysts for low-temperature catalytic combustion of methane were successfully prepared by synthetic induction of CuMn2O4 precursors via hydrothermal method which used deep eutectic solvent (DES) as an inducer. The structure and properties of the catalyst were investigated by XRD, BET, XPS and SEM characterizations to investigate the effect of DES addition on the crystal growth of the catalyst. The results showed that the Cu-Mn-C-O composite catalyst produced a new phase of MnCO3, which changed the number and distribution of acid-base sites on the catalyst surface and effectively promoted the desorption of catalytic reaction products. The catalytic activity test showed that the methane catalytic activity of the Cu-Mn-C-O composite catalyst was significantly enhanced at Mn/C molar ratio of 1:2.5, with T50 and T90 values of 365 °C and 425 °C, respectively. This can be attributed to the high proportional distribution of high-valent manganese in the internal electronic structure of the composite catalyst system, which generated a large number of surface adsorbed oxygen species and thus facilitated the oxidation of methane at lower temperatures. Thermal analysis of composite catalysts revealed relatively high activation energy and thermal stability in the combustion process of composite catalysts. This study will lead to innovative insights into the design of composite catalysts for methane oxidation.