Mn Centers Research Articles

Exploring the Water Oxidation Catalytic Activity of a Mn-Based Magnetic Metal-Organic Framework: The Role of Proton Conductivity and Oxygen Evolution Reaction Overpotential.

The present work evaluates the water oxidation catalytic activity of a Mn-based metal-organic framework (MOF), which we envisioned to reduce the oxygen evolution reaction (OER) overpotential because of its high electrical conductivity, facilitated by solvent-encapsulated structural features. The presence of Mn centers induces interesting magnetic features in the MOF, which exhibits impressive cryogenic magnetic refrigeration with a ΔSM value of 29.94 J kg-1 K-1 for a field change of ΔH = 5T at 2.3 K. To the best of our knowledge, the ΔSM value of the current system ranked the highest position among the published examples. The crystal structure aligns perfectly with the thematic expectations and features as many as ten metal-coordinated water molecules, forming an extensive web of a hydrogen-bonded network while facing toward the porous channel filled with another set of much-anticipated entrapped lattice water molecules. Such structural features are expected to manifest high proton conductivity, and detailed investigation indeed yields the best value for the system at 1.57 × 10-4 S/cm at 95% humidity and 85 °C. In order to evaluate the thematic notion of a one-to-one relationship between OER and improved electrical conductivity, extensive electrocatalytic water splitting (WS) investigations were carried out. The final results show highly encouraging WS ability of the Mn-MOF, showing the electrocatalytic surface area value of the active species as 0.0686 F/g with a turnover frequency value of 0.043 [(mol. O2) (mol. Mn-MOF)-1 s-1]. Another fascinating aspect of the current communication is the excellent synergy observed between the experimental WS outcomes and the corresponding theoretical data calculated using density functional theory (DFT). Consequently, a plausible mechanism of the overall OER and the role of the Mn-MOF as a water oxidation catalyst, along with the importance of water molecules, have also been derived from the theoretical calculations using DFT.

Expression of chiral molecular and supramolecular structure on enantioselective catalytic activity

Understanding the structure-function relationships encoded on chiral catalysts is important for investigating the fundamental principles of catalytic enantioselectivity. Herein, the synthesis and self-assembly of naphthalene substituted bis-l/d-histidine amphiphiles (bis-l/d-NapHis) in DMF/water solution mixture is reported. The resulting supramolecular assemblies featuring well-defined P/M nanoribbons (NRs). With combination of the (P/M)-NR and metal ion catalytic centers (Mn+ = Co2+, Cu2+, Fe3+), the (P)-NR-Mn+ as chiral supramolecular catalysts show catalytic preference to 3,4-dihydroxy-S-phenylalanine (S-DOPA) oxidation while the (M)-NR-Mn+ show enantioselective bias to R-DOPA oxidation. In contrast, their monomeric counterparts bis-l/d-NapHis-Mn+ display an inverse and dramatically lower catalytic selectivity in the R/S-DOPA oxidation. Among them, the Co2+-coordinated supramolecular nanostructures show the highest catalytic efficiency and enantioselectivity (select factor up to 2.70), while the Fe3+-coordinated monomeric ones show nearly racemic products. Analysis of the kinetic results suggests that the synergistic effect between metal ions and the chiral supramolecular NRs can significantly regulate the enantioselective catalytic activity, while the metal ion-mediated monomeric bis-l/d-NapHis were less active. The studies on association constants and activation energies reveal the difference in catalytic efficiency and enantioselectivity resulting from the different energy barriers and binding affinities existed between the chiral molecular/supramolecular structures and R/S-DOPA enantiomers. This work clarifies the correlation between chiral molecular/supramolecular structures and enantioselective catalytic activity, shedding new light on the rational design of chiral catalysts with outstanding enantioselectivity.

Amorphization of MOFs with rich active sites and high electronic conductivity for hydrazine oxidation

The applications of metal-organic frameworks (MOFs) in electrocatalysis are limited by the perfect crystalline nature with insufficient coordinatively unsaturated sites and low electronic conductivity. Here, we report an electrosynthesis method to induce rapid assembly of amorphous MOFs on carbon cloth (denoted as aMnFc’/CC), achieving the amorphization of MOFs with rich active sites and high electronic conductivity. The long-range disordered structure of aMnFc’/CC forms a large number of oxygen vacancies to modify the coordination and electronic structures of Mn sites. In the electrocatalytic hydrazine oxidation reaction (HzOR), the aMnFc’/CC electrocatalyst exhibits superior activity to its crystalline MOF counterparts. Density functional theory calculations reveal that the unsaturated Mn centers present in aMnFc’/CC facilitate efficient electron transfer while simultaneously lowering the free energy of the rate-determining step in the HzOR process.

Comparative study of Mn oxide catalysts on toluene oxidation: The effect of Mn valence electronic structures

Understanding the structure-activity relationship of Mn-based oxide catalysts is of great importance for the rational development of highly performance catalysts for VOCs catalytic oxidation. However, the knowledge of the electronic structure-catalytic oxidation activity relationship over Mn-based oxide catalysts is still limited. Herein, we investigated the typical MnxOy (Mn3O4, MnO2, and Mn2O3) with different valence electronic structures by using various characterizations and DFT calculations. The MnO2 exhibits superior intrinsic activities (RS, 1.14×10−9 mol·m−2·s−1) when compared with Mn3O4 (0.54×10−9 mol·m−2·s−1) and Mn2O3 (0.45×10−9 mol·m−2·s−1) for toluene catalytic oxidation. The solid experimental and DFT calculation results show that the d-band center of Mn determines the intrinsic activity. The superior catalytic oxidation activity of MnO2 can be attributed to its higher d-band center (-1.03 eV) in comparison with that of Mn3O4 (-1.25 eV) and Mn2O3 (-1.59 eV). The higher d-band center can weaken the surface Mn-O bonds strength (k = 290.9 N/m) and strengthen the gaseous O2 adsorption simultaneously, then enhancing the mobility of surface lattice oxygen and the amount of adsorbed oxygen species. This work firstly reveals the intrinsic relationship between catalytic oxidation activity and d electronic structure over Mn-based oxide catalysts and provides knowledge that will advance the design of high-performance catalysts for catalytic oxidation.

Zn(II), Mn(III), and Co(III) complexes of Schiff base derived from 2‐hydroxy‐1‐naphthaldehyde: Synthesis, spectral surveys, single crystal structure studies, Hirshfeld surface analysis, density functional theory calculation, molecular electrostatic potential, and molecular docking evaluations

A new series of transition metal complexes of bidentate Schiff base compound derived from 2‐hydroxy‐1‐(2‐methoxyethylimino)‐naphthalene (HL) were synthesized and characterized using elemental analysis, Fourier transform infrared spectroscopy (FT‐IR), and UV–vis spectroscopies. X‐ray single crystal structures of Zn(II), Mn(III), and Co(III) complexes (1–4) have also been determined, and it was indicated that these Zn(II) and Co(III) complexes (1, 4) are in an octahedral geometry. Whereas, it was found that the Zn complex (2) is in quite a regular tetrahedral environment. Also, the Mn center in complex (3) is ligated by two azomethine nitrogen atoms, two ligand oxygen atoms, and one Cl atom of metal salt forming five coordinated tetragonal pyramid geometry around the Mn atoms. The cyclic voltammetry of the complexes specifies an irreversible redox behavior for all complexes (1–4). Next, DFT/B3LYP theoretical method was used to determine the optimal geometrical configurations and comparison between experimental and theoretical data, as well as for calculations of molecular electrostatic potential, highest‐occupied molecular orbital (HOMO)‐lowest‐unoccupied molecular orbital (LUMO) energy values of selected compounds. The study of non‐covalent interactions was done by Hirshfeld surface analysis using CrystalExplorer program. Furthermore, molecular docking inspection was carried out to study the binding affinity of the tested complexes towards protein B‐cell lymphorna (PDB ID: 4LXD). Using the results obtained from the molecular docking and the summarized interaction of the binding processes, these structures show the validity of effective inhibition against liver cancer.

Robust Room Temperature Thermoelectric Performance of Mg3(Sb, Bi)2‐Based Alloys via Multivalent Mn Doping

Abstractn‐type Mg3(Sb, Bi)2 has excellent room temperature thermoelectric performance, which is, however, severely restricted by the negatively charged Mg vacancies that significantly deteriorate the carrier mobility. Herein, by manipulating the threshold solubility and defect formation energy of Mn, multivalent Mn is selectively introduced that synergistically promotes the carrier conduction according to different Mg chemical potentials; In Mg‐rich areas, interstitial Mn dominates which effectively reduces the migration and accumulation of Mg vacancies, while in Mg poor areas, interstitial Mn switches to substitutional sites that directly compensate for the negative charge. All the Mn centers possess Jahn–Teller inactive positions, leading to an ultra‐stable room temperature thermoelectric performance with a leading ZT up to 0.97. This work reveals the critical effect of multivalent and multifunctional transition metal incorporation in Mg3(Sb, Bi)2‐based alloys toward high room‐temperature thermoelectric performance.

Boundary-Rich Carbon-Based Electrocatalysts with Manganese(II)-Coordinated Active Environment for Selective Synthesis of Hydrogen Peroxide.

Coordinated manganese (Mn) electrocatalysts owing to their electronic structure flexibility, non-toxic and earth abundant features are promising for electrocatalytic reactions. However, achieving selective hydrogen peroxide (H2 O2 ) production through two electron oxygen reduction (2e-ORR) is a challenge on Mn-centered catalysts. Targeting this goal, we report on the creation of a secondary Mn(II)-coordinated active environment with reactant enrichment effect on boundary-rich porous carbon-based electrocatalysts, which facilitates the selective and rapid synthesis of H2 O2 through 2e-ORR. The catalysts exhibit nearly 100 % Faradaic efficiency and H2 O2 productivity up to 15.1 mol gcat -1 h-1 at 0.1 V versus reversible hydrogen electrode, representing the record high activity for Mn-based electrocatalyst in H2 O2 electrosynthesis. Mechanistic studies reveal that the epoxide and hydroxyl groups surrounding Mn(II) centers improve spin state by modifying electronic properties and charge transfer, thus tailoring the adsorption strength of *OOH intermediate. Multiscale simulations reveal that the high-curvature boundaries facilitate oxygen (O2 ) adsorption and result in local O2 enrichment due to the enhanced interaction between carbon surface and O2 . These merits together ensure the efficient formation of H2 O2 with high local concentration, which can directly boost the tandem reaction of hydrolysis of benzonitrile to benzamide with nearly 100 % conversion rate and exclusive benzamide selectivity.

Boundary‐Rich Carbon‐Based Electrocatalysts with Manganese(II)‐Coordinated Active Environment for Selective Synthesis of Hydrogen Peroxide

AbstractCoordinated manganese (Mn) electrocatalysts owing to their electronic structure flexibility, non‐toxic and earth abundant features are promising for electrocatalytic reactions. However, achieving selective hydrogen peroxide (H2O2) production through two electron oxygen reduction (2e‐ORR) is a challenge on Mn‐centered catalysts. Targeting this goal, we report on the creation of a secondary Mn(II)‐coordinated active environment with reactant enrichment effect on boundary‐rich porous carbon‐based electrocatalysts, which facilitates the selective and rapid synthesis of H2O2 through 2e‐ORR. The catalysts exhibit nearly 100 % Faradaic efficiency and H2O2 productivity up to 15.1 mol gcat−1 h−1 at 0.1 V versus reversible hydrogen electrode, representing the record high activity for Mn‐based electrocatalyst in H2O2 electrosynthesis. Mechanistic studies reveal that the epoxide and hydroxyl groups surrounding Mn(II) centers improve spin state by modifying electronic properties and charge transfer, thus tailoring the adsorption strength of *OOH intermediate. Multiscale simulations reveal that the high‐curvature boundaries facilitate oxygen (O2) adsorption and result in local O2 enrichment due to the enhanced interaction between carbon surface and O2. These merits together ensure the efficient formation of H2O2 with high local concentration, which can directly boost the tandem reaction of hydrolysis of benzonitrile to benzamide with nearly 100 % conversion rate and exclusive benzamide selectivity.

Electrocatalytic water oxidation with manganese phosphates

As inspired by the Mn4CaO5 oxygen evolution center in nature, Mn-based electrocatalysts have received overwhelming attention for water oxidation. However, the understanding of the detailed reaction mechanism has been a long-standing problem. Herein, homologous KMnPO4 and KMnPO4•H2O with 4-coordinated and 6-coordinated Mn centers, respectively, are prepared. The two catalysts constitute an ideal platform to study the structure-performance correlation. The presence of Mn(III), Mn(IV), and Mn(V) intermediate species are identified during water oxidation. The Mn(V)=O species is demonstrated to be the substance for O−O bond formation. In KMnPO4•H2O, the Mn coordination structure did not change significantly during water oxidation. In KMnPO4, the Mn coordination structure changed from 4-coordinated [MnO4] to 5-coordinated [MnO5] motif, which displays a triangular biconical configuration. The structure flexibility of [MnO5] is thermodynamically favored in retaining Mn(III)−OH and generating Mn(V)=O. The Mn(V)=O species is at equilibrium with Mn(IV)=O, the concentration of which determines the intrinsic activity of water oxidation. This study provides a clear picture of water oxidation mechanism on Mn-based systems.

Spectroscopic Characterization of Mn1+ Low Oxidation State in Prussian Blue-Based Battery Anodes.

Stabilization of ions in exotic oxidation states is beneficial for the development of new materials for green energy technologies. Exotic Mn1+ was proposed to play a role in the function of sodium-based Prussian blue analogues (PBA) batteries, a highly sought-out technology for industrial energy storage. Here, we report the detailed electronic structure characterization of uncharged and charged sodium-based manganese hexacyanomanganate anodes via Mn K-edge X-ray absorption spectroscopy (XAS), Kβ nonresonant X-ray emission (XES), and resonant inelastic X-ray scattering (RIXS). The latter allowed us to obtain site-selective XANES information about two distinct Mn centers. The obtained spectroscopic data represent the first electronic structure characterization of low-spin Mn1+ using hard X-ray RIXS and XES and allowed us to confirm its role in anode reduction. Our experimental approach can be expanded to analysis of analogues with other 3d transition metals broadening the application of exotic ionic states in materials engineering.

Effect of Variable Amine Pendants in the Secondary Coordination Sphere of Manganese Bipyridine Complexes on the Electrochemical CO2 Reduction

AbstractThe increasing concentration of CO2 in the atmosphere and its impact on the climate are matters of significant concern. Extensive research is being conducted on molecular catalysts to electrochemically reduce CO2 into valuable products to disrupt the unidirectional carbon flow. This study compares two manganese bipyridine catalysts, tailored with four or two benzylic diethylamine groups in the secondary coordination sphere. Either of these amine‐bearing scaffolds positioned close to the Mn center serves as effective proton relays to facilitate the formation of the corresponding Mn hydride intermediate. Alongside competitive H2 evolution, the reaction of this crucial intermediate with CO2 leads to formate. Our findings underscore the pronounced influence of external Brønsted acids on product selectivity. Notably, when employing the catalyst bearing four amine groups, the HCOO−/H2 ratio varies from 81 : 3 with 1.0 M iPrOH to 16 : 64 with 1.0 M PhOH, while the Mn complex adorned with two amine pendant groups consistently favors HCOO−, irrespective of the utilized proton sources. Infrared spectroelectrochemistry and density‐functional theory calculations unveil distinct disparities in the reactivity of the Mn hydrides toward CO2 due to the change of ligand bulkiness in the two cases. This work substantiates the importance of modulating spatial accessibility while modifying the second sphere encompassing molecular catalysts.

Controlling product selectivity during dioxygen reduction with Mn complexes using pendent proton donor relays and added base.

The catalytic reduction of dioxygen (O2) is important in biological energy conversion and alternative energy applications. In comparison to Fe- and Co-based systems, examples of catalytic O2 reduction by homogeneous Mn-based systems is relatively sparse. Motivated by this lack of knowledge, two Mn-based catalysts for the oxygen reduction reaction (ORR) containing a bipyridine-based non-porphyrinic ligand framework have been developed to evaluate how pendent proton donor relays alter activity and selectivity for the ORR, where Mn(p-tbudhbpy)Cl (1) was used as a control complex and Mn(nPrdhbpy)Cl (2) contains a pendent -OMe group in the secondary coordination sphere. Using an ammonium-based proton source, N,N'-diisopropylethylammonium hexafluorophosphate, we analyzed catalytic activity for the ORR: 1 was found to be 64% selective for H2O2 and 2 is quantitative for H2O2, with O2 binding to the reduced Mn(ii) center being the rate-determining step. Upon addition of the conjugate base, N,N'-diisopropylethylamine, the observed catalytic selectivity of both 1 and 2 shifted to H2O as the primary product. Interestingly, while the shift in selectivity suggests a change in mechanism for both 1 and 2, the catalytic activity of 2 is substantially enhanced in the presence of base and the rate-determining step becomes the bimetallic cleavage of the O-O bond in a Mn-hydroperoxo species. These data suggest that the introduction of pendent relay moieties can improve selectivity for H2O2 at the expense of diminished reaction rates from strong hydrogen bonding interactions. Further, although catalytic rate enhancements are observed with a change in product selectivity when base is added to buffer proton activity, the pendent relays stabilize dimer intermediates, limiting the maximum rate.

Efficient net transfer-dehydrogenation of glycerol: NNN pincer-Mn and manganese chloride as a catalyst unlocks the effortless production of lactic acid and isopropanol.

Herein, a series of pincer-Mn complexes based on bis(imino)pyridine ligands of the type R2NNN (R = tBu, iPr, Cy and Ph) were synthesized and characterized using various spectroscopic techniques. SCXRD studies revealed a trigonal bipyramidal geometry around the metal center in all the complexes. EPR spectroscopy confirmed the presence of high-spin Mn(II) centers with the consistent observation of sextets in EPR spectra. Additionally, solution magnetic moment measurement exhibited values ranging from 5.8 to 6.2 BM for all the complexes, which are in accordance with the theoretical value of 5.92 BM. HRMS analysis complemented structural characterization, showing fragments corresponding to various solvent adducts and derivatives of the complexes. Subsequently, the synthesized complexes were investigated for their catalytic activity in the transfer dehydrogenation of glycerol to lactic acid in the presence of acetone. Among the considered complexes, the catalyst Ph2NNNMnCl2 was found to be highly efficient. Remarkably, a yield of 92% LA was observed with >99% selectivity at 0.5 mol% loading of Ph2NNNMnCl2 in the presence of 1 equivalent of NaOH at 140 °C in 24 h, surpassing the yield obtained from its precursor MnCl2·4H2O, where a yield of 72% LA was observed with 96% selectivity under similar reaction conditions. This catalytic system was further investigated with a range of acceptors, and good to moderate yields were observed in most cases. Moreover, several control experiments, including reaction with PPh3, CS2 and Hg, highlighted the major involvement of molecular species in the reaction medium. Deuterium labelling studies indicated the involvement of C-H bond activation in the catalytic cycle but not in the rate-determining step (RDS), with a secondary kinetic isotope effect (KIE) of 1.25.

Manganese matere bonds in biological systems: PDB inspection and DFT calculations.

A Protein Data Bank (PDB) survey has revealed noncovalent contacts involving Mn centres and protein residues. Their geometrical features are in line with the interaction between low electron density sites located along the Mn-O/N coordination bonds (σ-holes) and the lone pairs belonging to TYR, SER or HIS residues, known as a matere bond (MaB). Calculations at the PBE0-D3/def2-TZVP level of theory were used to investigate the strength and shed light on the physical nature of the interaction. We expect the results presented herein will be useful for those scientists working in the fields of bioinorganic chemistry, particulary in protein-metal docking, by providing new insights into transition metal⋯Lewis base interactions as well as a retrospective point of view to further understand the structural and functional implications of this key transition metal ion.

Enhancing the catalytic activity of the MnNC catalyst by regulating the coordination environment.

The catalytic activity is largely determined by the coordination environment of the active sites. The catalytic activity of MnNC was much enhanced by the regulation of the coordination environment. The introduction of optimal epoxy to the vicinity of the Mn centers improved its half-wave potential by ∼300 mV.

Efficient catalytic ozonation for ibuprofen through electron-deficient/rich centers over cerium-manganese doped carbon

The sluggish Me(n+m)+/Men+ redox cycle greatly restrained the catalytic ozonation performance of metal-based catalysts. To break this bottleneck, we adopted an interfacial oxidation reaction to create electron-deficient/rich centers within carbon skeleton derived from MOF (C-MOF) by utilizing the electronegativity difference between cerium (Ce) and manganese (Mn), and evaluated its catalytic ozonation activity with ibuprofen (IBP) as model pollutant. XPS, H2-TPR, LSV and EPR characterizations as well as DFT calculation demonstrated that there existed electron-deficient Ce sites and electron-rich Mn sites on CeOx/MnOx/C-MOF. Under the co-function of Ce and Mn sites, CeOx/MnOx/C-MOF/O3 process achieved 100% IBP removal in 90 min, which was 3.1 times of sole ozonation process. IBP could be absorbed at the electron-deficient Ce center and directionally donate its electron to the O3 around electron-rich Mn center. Singlet oxygen (1O2) played the major role in IBP degradation. Cl−, HCO3−, NO3− and SO42− demonstrated limited inhibitions on IBP degradation. This work provided a sustainable strategy for breaking the rate-limiting step in the traditional catalytic ozonation.

Influence of the ancillary ligand on the crystalline structures and magnetic properties of mesaconato‐bridged Mn coordination polymers

Abstract{[Mn(mes)(dmb)(H2O)] ⋅ H2O}n (1) and [Mn(mes)(bpy)]n (2); (mes=mesaconato; dmb=5,5’‐dimethyl‐2,2’‐bipyridine; bpy=2,2’‐bipyridine), were obtained by self‐assembly solution reaction at ambient conditions, and structurally characterized by single crystal X‐ray diffraction. 1 crystallizes in an orthorhombic system with a Pbca space group and forms a one‐dimensional (1D) coordination polymer; the six‐coordinated Mn(II) centers display a distorted‐trigonal prismatic configuration. 2 crystallizes in an orthorhombic system with a P21212 space group yielding a two‐dimensional (2D) coordination array, their metal centers having a distorted octahedral geometry. Magnetic susceptibility measurements reveal that 1 is paramagnetic, while 2 shows weak antiferromagnetic coupling.

Hierarchical bimetallic metal-organic frameworks with controllable assembling sub-units and interior architectures for enhanced ammonia detection

A series of hierarchical three-dimensional (3D) manganese-cobalt BTC (Mn-Co BTC; BTC = benzene-1,3,5-tricarboxylate ) metal–organic frameworks (MOFs) with controllable sub-units and interior architectures have been synthesized at room temperature without templates, etchants, or high-pressure conditions. The assembling sub-units of the hierarchical 3D Mn-Co BTC MOFs can be controlled by tuning the Mn/Co ratio, with higher Mn content favoring one-dimensional (1D) sub-units, while higher Co content favors two-dimensional (2D) sub-units. The hierarchical hollow Mn-Co BTC spheres (M2C-BTC) exhibit a frequency change (ΔF) of 383.7 Hz to 69.5 ppm of NH3 which is ∼1.7-, 2.1-, 4.2-, and 8.3-times higher than the ΔFs of hierarchical Mn-Co BTC nanorods (M1C-BTC), hierarchical flower-like Mn-Co BTC (M0.5C-BTC), Mn-BTC nanospheres, and Co-BTC nanoplates, respectively. In addition, they exhibit low limit of detection (1.12 ppm), high selectivity (41 %) and excellent stability for NH3 sensing with a minor change of 3.1 % in the ΔF value after 5 months of testing. The superior NH3 sensing performance of the hierarchical hollow Mn-Co BTC spheres may be attributed to the hollow cavities which can enhance the adsorption rate of NH3 molecules (based on the adsorption kinetics analysis) and enable them to interact with the less accessible metallic active sites on the inner cores of this MOF. The possible sensing mechanisms include the chemisorption of NH3 molecules on unsaturated metal (Mn and Co) centers as well as the hydrogen bonding between the hydroxyl and carboxyl groups with NH3.

Catalytic oxidation of thymol and carvacrol with Mn(II)-benzoylbenzoate-bipyridine complex

The primary focus of catalytic chemistry is the synthesis of valuable chemicals from cheaper and more abundant substrates. The main objective of catalytic processes is to achieve higher yields at affordable costs under environmentally friendly conditions. Under homogeneous conditions, the synthesized bimetallic Mn(II) complex with (2-benzoylbenzoic acid, bba) and N,N coordinated (2,2-bipyridine, bipy) ligands, [Mn2(μ1,3-(C6H5)CO(C6H4)COO)2(bipy)2].2ClO4 is shown to be an active catalyst for the oxidation of monoterpenes (thymol and carvacrol), using TBHP under mild reaction conditions. The structure of the complex was characterized by single-crystal X-ray diffraction. The six-coordinated Mn(II) centers bridge in a coordination pattern due to the monodentate bonding mode of the carboxylate oxygen atoms of benzoylbenzoate anion. The selectivity of the Mn-catalyst was measured to be 100 % for thymol and carvacrol to thymoquinone. A simple, effective and selective Mn(II)/TBHP/Monoterpene/CH3CN catalyst system was used for the oxidation of thymol (TOF = 2000 h−1, in 15 min) and carvacrol (TOF = 667 h−1, in 45 min.) into a valuable product, thymoquinone (TQ), in acetonitrile at 80 °C.

Interfacial confinement effect induced by pre-sulfurization for promoting SO2 tolerance of MnFe-TOS catalyst in low temperature NH3-SCR reaction

SO2 poisoning still is an unresolved problem for NH3-SCR catalysts, especially under low temperature conditions. Herein, a two-pronged approach has been applied on MnFe-TOS for promoting SO2 tolerance at low temperature in NH3-SCR process. Pre-sulfurization via inserting SO42- into TiO2 lattice perturbed the local electronic environment to supplement rich surface acid sites, promoting the rapid adsorption of NH3 at reaction temperature. Active −NH2 and NH4+ could be quickly consumed by NO/nitrites via both L-H and E-R reaction pathway and resulted in high N2 selectivity. The strong interaction of Mn–O–Fe induced by interfacial confinement effect regulated redox ability and inhibited the adsorption/oxidation of SO2, which was benefited to NO activation on MnFe-TOS. At the same time, the (NH4)2SO4 generated during the NH3-SCR process was prone to dissociation into NH4+ and SO42-, where NH4+ continued to participate in the SCR reaction, while SO42- bonded to Fe, as a functional protective site, allowing the Mn site to be protected. DFT calculations have provide convincing evidence at the molecular level to demonstrate how pre-sulfurization induced lattice distortion and affected chemical adsorption characteristics of catalytic active centers (Mn–O–Fe–S). Consequently, the MnFe-TOS exhibited excellent resistance to SO2 at low temperature, and the N2 selectivity has been improved during a wide temperature window. This study provides a new approach for designing efficient and stable NH3-SCR catalysts.