Catalysts For Oxidation Reactions Research Articles

Surface modification of multi-walled carbon nanotubes to produce a new bimetallic Fe/Mn catalyst for the aerobic oxidation of hydrocarbons

Fe/Mn bimetallic heterogenized catalyst [Fe/Mn(THPP)@MWCNT] was prepared by the simultaneous attachment of Mn and Fe porphyrins onto the surface of functionalized multi-walled carbon nanotubes. This new bimetallic nanohybrid displays a superior catalytic performance (81%) in comparison with their analogous monometallic counterparts (36% and 44% for Fe- and Mn-porphyrin respectively) in the oxidation of hydrocarbons with molecular oxygen as the sole oxidant. Experiments comparing bimetallic catalyst with equivalent physical mixtures of monometallic catalysts revealed the catalytic synergistic effect amongst metallic active centers onto the surface of the same nanotube, introducing a new class of bimetallic porphyrin-based catalysts for oxidation reactions.

Interaction between Ruthenium Oxide Surfaces and Water Molecules. Effect of Surface Morphology and Water Coverage

RuO2 is a conducting transition metal oxide that has unique redox properties to be used as heterogeneous catalyst for oxidation reactions as well as in electrocatalysis. Furthermore, it has been reported to be an excellent catalyst for the oxygen evolution reaction, a key step for obtaining energy from water through environmentally friendly processes. In this context, a detailed knowledge of the RuO2–water interface is important for a better understanding of the electrochemical process, the water oxidation reaction and some oxidative reactions involving RuO2. Here, we use periodic boundary condition DFT (PBE-D2) calculations to analyze the influence of the surface morphology and water coverage in the adsorption energies and degree of water deprotonation. We have considered the four nonpolar ((110), (011), (100), and (001)) most relevant surfaces and three degrees of water coverage: isolated molecules, half monolayer and full monolayer. Results indicate that three effects are crucial for determining the ad...

Operando Insights into CO Oxidation on Cobalt Oxide Catalysts by NAP-XPS, FTIR, and XRD.

Cobalt oxide Co3O4 has recently emerged as promising, noble metal-free catalyst for oxidation reactions but a better understanding of the active catalyst under working conditions is required for further development and potential commercialization. An operando approach has been applied, combining near ambient (atmospheric) pressure X-ray photoelectron spectroscopy (NAP-XPS), Fourier transform infrared spectroscopy (FTIR), or X-ray diffraction (XRD) with simultaneous catalytic tests of CO oxidation on Co3O4, enabling one to monitor surface and bulk states under various reaction conditions (steady-state and dynamic conditions switching between CO and O2). On the basis of the surface-specific chemical information a complex network of different reaction pathways unfolded: Mars-van-Krevelen (MvK), CO dissociation followed by carbon oxidation, and formation of carbonates. A possible Langmuir–Hinshelwood (LH) pathway cannot be excluded because of the good activity when no oxygen vacancies were detected. The combined NAP-XPS/FTIR results are in line with a MvK mechanism above 100 °C, involving the Co3+/Co2+ redox couple and oxygen vacancy formation. Under steady state, the Co3O4 surface appeared oxidized and the amount of reduced Co2+ species at/near the surface remained low up to 200 °C. Only in pure CO, about 15% of surface reduction were detected, suggesting that the active sites are a minority species. The operando spectroscopic studies also revealed additional reaction pathways: CO dissociation followed by carbon reoxidation and carbonate formation and its decomposition. However, due to their thermal stability in various atmospheres, the carbonates are rather spectators and also CO dissociation seems a minor route. This study thus highlights the benefits of combining operando surface sensitive techniques to gain insight into catalytically active surfaces.

Identifying Influential Parameters of Octahedrally Coordinated Cations in Spinel ZnMnxCo2–xO4 Oxides for the Oxidation Reaction

Transition metal oxides are potential alternatives to precious metal catalysts for oxidation reactions. Among these earth abundant oxide catalysts, cobalt- or manganese-based spinel oxides have attracted consistent interest because of their superior catalytic performances. It has been found that the octahedral sites in spinels are responsible for their catalytic activities. However, little is known about the parameters of the octahedrally coordinated cations that influence their activity. Herein, a series of ZnMnxCo2–xO4 (x = 0–2.0) spinel oxides are investigated, employing CO oxidation as the model reaction, with particular attention being paid to the variation in activity caused by tuning the ratio of octahedrally occupied Mn to Co. Both Mn and Co contribute to the activity with Mn cations as the primary active species when they coexist; the intrinsic specific activity is found to be dependent on composition, and the highest activity is seen at a Mn/Co molar ratio of 0.11. The presence of Mn4+ and Mn3+ ...

Cu(II)-Schiff base covalently anchored to MIL-125(Ti)-NH2 as heterogeneous catalyst for oxidation reactions

MIL-125(Ti)-NH2 has been modified by reaction of salicylaldehyde with the terephthalate amino groups to form a salicylideneimine that act as ligand of Cu2+. The success of the postsynthetic modification was assessed by FTIR spectroscopy of the MIL-125(Ti)-NH2-Sal-Cu and by analysis by 1H NMR spectroscopy of the organic linkers upon dissolution of MIL-125(Ti)-NH2-Sal-Cu. In comparison with parent MIL-125(Ti)-NH2 and MIL-125(Ti)-NH2-Sal, that exhibit a poor activity, the presence of the Cu-Schiff base complex in MIL-125(Ti)-NH2-Sal-Cu catalyst for the oxidation of 1-phenylethanol by tert-butylhydroperoxyde (TBHP, 3 eq.) increases notably the catalytic activity. Hot filtration test and reusability experiments confirm that the process is heterogeneous and that MIL-125(Ti)-NH2-Sal-Cu is stable under the reaction conditions. Quenching studies and EPR spectra using N-tbutylphenylnitrone indicate the generation of tBuOO and tBuO under the reaction conditions. The scope of MIL-125(Ti)-NH2-Sal-Cu as oxidation catalyst by tBuOOH was studied for benzyl alcohol as well as alicyclic and aliphatic alcohols and ethylbenzene.

Efficient oxidative dehydrogenation of ethanol by VOx@MIL-101: On par with VOx/ZrO2 and much better than MIL-47(V)

The possibility to apply metal organic framework (MOF) based catalysts for oxidation reaction in gas phase was explored. Catalytic activity of the vanadium oxide catalyst incorporated in MIL-101(Cr) as support was investigated in gas phase ethanol oxidative dehydrogenation (EtOH-ODH) and compared to that of MIL-47(V) metal organic framework material containing vanadium as central metal in the framework structure and to a classical VOx/ZrO2 supported vanadium oxide catalyst. It was found that vanadium species, incorporated in MIL-101(Cr) support by a variant of vapor deposition method, are stabilized in the form of well dispersed VOx species (no vanadium pentoxide clusters was detected in the catalyst). The obtained VOx@MIL-101(Cr) catalyst exhibited high selectivity towards acetaldehyde (up to 99%) at reaction temperatures not exceeding 200 °C. The catalytic activity of VOx@MIL-101(Cr) catalyst reached an activity level comparable to that of the classical VOx/ZrO2 catalyst, but the specific productivity of acetaldehyde (3 kgAA kgcat−1 h−1) was higher by 75% compared with productivity on VOx/ZrO2 due to much higher content of vanadium species, which could be hosted by the MOF. On the other hand, MIL-47(V) catalyst exhibited negligible activity seemingly due to coordinatively saturated character of the vanadium centers and/or too high stability of the VIV oxidation state. This proof-of-concept study proved that application of MOF materials as host matrices for heterogeneous catalysts aiming oxidation reaction in gas phase could be efficient as demonstrated on the example of oxidative dehydrogenation of ethanol.

Adsorption-Based Synthesis of Environmentally Friendly Heterogeneous Chromium(III) Catalysts for Oxidation Reactions into Kaolinite, Saponite, and Their Amine-Modified Derivatives

Batch experiments were used to evaluate the Brazilian Sao Simao kaolinite (Kao), the Spanish Yuncillos saponite (Sa), and their derivatives organofunctionalized with 3-aminopropyltriethoxysilane (K...

Vanadium Complexes Based Polymer Supported Catalysts: A Brief Account of Research from Our Group

Solid supported catalysts can go a long way in developing catalyst based technology because of their high efficiency with recyclability and easy separation from the reaction mixture. Immobilizations of homogeneous catalysts through covalent bond with chloromethylated polystyrene cross-linked with divinylbenzene and develop them as environmentally safe heterogeneous catalysts for oxidation reaction have attracted attention in recent years. Recently, effort from our research laboratory was to synthesize new recyclable polymer-supported vanadium complexes based heterogeneous catalysts. Thus, chloromethylated polystyrene cross linked with 5% divinylbenzene was used as support to prepare variety of polymer supported vanadium catalysts. These catalysts have successfully been used for the oxidation and oxidative bromination of various organic substrates. Keeping in mind the industrial usage of these heterogeneous catalysts, the leaching and recycle ability of all polymer-supported catalysts have also been tested. Most catalysts are stable and do not leach during the catalytic reactions.

Styrene-co-divinylbenzene/silica hybrid supports for immobilization transitional metals and their application in catalysis

The functionalization of S–1% DVB copolymer was carried out with aminophosphonate groups, and then the samples were covered with silica to obtain hybrid materials. The obtained hybrid materials were used as supports for impregnation of transition metal ions [Cu(II) and Mn(II)], and they were subsequently used as catalysts in oxidation reactions. The supports and catalysts were characterized by FTIR and UV–Vis spectroscopy, thermal analysis, SEM, and TEM electron microscopy. The results of FTIR spectroscopy indicated the formation of a hybrid of silica and an aminophosphonate polymer by the sol–gel route. The UV–Vis spectra showed a strong interaction of Cu(II) and a weak interaction of Mn(II) with aminophosphonate groups of the supports. The catalytic tests confirm different interactions between the metal cations and obtained supports. The formation of the immobilized Cu(II) complexes shows the possibility of using these materials selectively in oxidation of various organic compounds (anisole, cyclohexene, toluene, styrene, phenol). The purpose of this article is to develop some new poly(aminophosphonates)/silica hybrid materials immobilized with transition metal such as Cu(II) and Mn(II) ions for future use in the oxidation process.

Tetramethylpiperidine N-Oxyl (TEMPO), Phthalimide N-Oxyl (PINO), and Related N-Oxyl Species: Electrochemical Properties and Their Use in Electrocatalytic Reactions.

N-Oxyl compounds represent a diverse group of reagents that find widespread use as catalysts for the selective oxidation of organic molecules in both laboratory and industrial applications. While turnover of N-oxyl catalysts in oxidation reactions may be accomplished with a variety of stoichiometric oxidants, N-oxyl reagents have also been extensively used as catalysts under electrochemical conditions in the absence of chemical oxidants. Several classes of N-oxyl compounds undergo facile redox reactions at electrode surfaces, enabling them to mediate a wide range of electrosynthetic reactions. Electrochemical studies also provide insights into the structural properties and mechanisms of chemical and electrochemical catalysis by N-oxyl compounds. This review provides a comprehensive survey of the electrochemical properties and electrocatalytic applications of aminoxyls, imidoxyls, and related reagents, of which the two prototypical and widely used examples are 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO) and phthalimide N-oxyl (PINO).

Development of Ni-Based Bimetallic Electrocatalysts for Hydrogen Oxidation Reaction in Alkaline Fuel Cells

Anion exchange membrane fuel cells (AEMFCs) opens up the possibility of using non-platinum and/or non-platinum group metals (PGM) as electrocatalysts for both hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR). However, the slow kinetics of HOR along with the current lack of a durable and highly conducting OH- ion membrane remain major bottlenecks limiting its practical application. HOR with PGM free catalysts are still in the early stages of research unlike ORR with non-PGM catalysts1 . In order to overcome this limitation it is important to understand the mechanism of the HOR on the surface of the electro catalysts. It is considered that the two main descriptors, which enhance the electrocatalytic activity of the HOR, are the OHad or Had molecules on the surface of the catalytic materials.2,3 Ni and its alloys with transition metals would be one of the alternative choices for the HOR as Raney Ni and some of the Ni based alloys have been found showing improved HOR activity.4 Morphology, size and surface of the metallic nanoparicles have significant role on the catalytic activity in their respective applications. In this work we have synthesized monodispersed NiCo, NiCu and NiFe based bimetallic alloy nanoparticles of less than 20 nm size by high temperature solvothermal process.5 The synthesized alloy nanoparticles have been evaluated for their electrocatalytic activity and stability towards the HOR in a conventional rotating disk electrode (RDE) configuration tehnique. The nanoparticles have also been characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) to understand their physicochemical properties. The effect of surface state and alloying of the nanoparticles on the HOR kinetics is studied and analyzed in terms of mechanism and reaction steps involved. Our overall ambition in this work is to explore PGM free bi and trimetallic nanoparticles (NiM and NiMN) for the HOR and use them as anode catalysts in an operating AEM fuel cells. References Zhuang, Z. et al. Nickel supported on nitrogen-doped carbon nanotubes as hydrogen oxidation reaction catalyst in alkaline electrolyte. Nat.Commun. 7, 10141(2016).Strmcnik, D. et al. Improving the hydrogen oxidation reaction rate by promotion of hydroxyl adsorption. Nat.chem. 5,300-306 (2013).Parsons, R.The rate of electrolytic hydrogen evolution and the heat of adsorption of hydrogen.Trans. Faraday Soc. 54, 1053–1063 (1958).Kabir, S. et al. Platinum group metal-free NiMo hydrogen oxidation catalysts: high performance and durability in alkaline exchange membrane fuel cells. Jour.Mater.Chem. A, (2017).Carenco,S. et al.Controlled design of size-tunable monodisperse nickel nanoparticles.Chem.Mater.22,1340-1349(2010). Figure 1:Representative bright field scanning transmission electron microscopy (STEM) image of bimetallic NiCo nanoparticles Figure 1

(Energy Technology Division Research Award Address) Hydroxide Exchange Membrane Fuel Cells for Affordable Zero-Emission Cars

One of the grand challenges facing humanity today is the development of an alternative energy system that is safe, clean, and sustainable and where combustion of fossil fuels no longer dominates. A distributed renewable electrochemical energy and mobility system (DREEMS) could meet this challenge1. At the foundation of this new energy system, we have chosen to study a number of electrochemical devices including fuel cells, electrolyzers, and flow batteries. For all these devices electrocatalysis and polymer electrolytes play a critical role in controlling their performance, cost, and durability, and thus their economic viability. In this presentation, I will focus on our work on hydroxide exchange membrane fuel cells (HEMFCs)2 which can work with nonprecious metal catalysts3 and inexpensive hydrocarbon polymer membranes4. More specifically I will show the roadmap we have developed for HEMFCs to achieve performance parity with proton exchange membrane fuel cells5, the progress we have made in developing the most stable membranes and the most active nonprecious metal catalysts6. I will also discuss our work on addressing cell/system level issues like reverse current decay and water management7-9, and why hydrogen oxidation reactions are slower in base than in acid for precious metal catalysts10-12. References (1) S. Gu, B. Xu, Y. Yan. Electrochemical Energy Engineering: A New Frontier of Chemical Engineering Innovation. Annual Review of Chemical and Biomolecular Engineering 2014, 5: 429-454. (2) S. Gu, R. Cai, T. Luo, Z. Chen, M. Sun, Y. Liu, G. He, Y. Yan. A Soluble and Highly Conductive Ionomer for High-Performance Hydroxide Exchange Membrane Fuel Cells. Angewandte Chemie-International Edition 2009, 48(35): 6499-6502. (3) S. Gu, W. Sheng, R. Cai, S. M. Alia, S. Song, K. O. Jensen, Y. Yan. An efficient Ag-ionomer interface for hydroxide exchange membrane fuel cells. Chemical Communications 2013, 49(2): 131-133. (4) S. Gu, J. Wang, R. B. Kaspar, Q. Fang, B. Zhang, E. B. Coughlin, Y. Yan. Permethyl Cobaltocenium (Cp-2*Co+) as an Ultra-Stable Cation for Polymer Hydroxide-Exchange Membranes. Scientific Reports 2015, 5. (5) B. P. Setzler, Z. Zhuang, J. A. Wittkopf, Y. Yan. Activity targets for nanostructured platinum group-metal-free catalysts in hydroxide exchange membrane fuel cells. Nature Nanotechnology 2016, 11(12): 1020-1025. (6) Z. Zhuang, S. A. Giles, J. Zheng, G. R. Jenness, S. Caratzoulas, D. G. Vlachos, Y. Yan. Nickel supported on nitrogen-doped carbon nanotubes as hydrogen oxidation reaction catalyst in alkaline electrolyte. Nature Communications 2016, 7. (7) R. B. Kaspar, Y. Yan. Communication-Patterned Electrodes to Increase Water Back-Diffusion in Hydroxide Exchange Membrane Fuel Cells. Journal of the Electrochemical Society 2016, 163(7): F593-F595. (8) R. B. Kaspar, J. A. Wittkopf, M. D. Woodroof, M. J. Armstrong, Y. Yan. Reverse-Current Decay in Hydroxide Exchange Membrane Fuel Cells. Journal of the Electrochemical Society 2016, 163(5): F377-F383. (9) R. B. Kaspar, M. P. Letterio, J. A. Wittkopf, K. Gong, S. Gu, Y. Yan. Manipulating Water in High-Performance Hydroxide Exchange Membrane Fuel Cells through Asymmetric Humidification and Wetproofing. Journal of the Electrochemical Society 2015, 162(6): F483-F488. (10) W. Sheng, M. Myint, J. G. Chen, Y. Yan. Correlating the hydrogen evolution reaction activity in alkaline electrolytes with the hydrogen binding energy on monometallic surfaces. Energy & Environmental Science 2013, 6(5): 1509-1512. (11) W. Sheng, Z. Zhuang, M. Gao, J. Zheng, J. G. Chen, Y. Yan. Correlating hydrogen oxidation and evolution activity on platinum at different pH with measured hydrogen binding energy. Nature Communications 2015, 6. (12) J. Zheng, W. Sheng, Z. Zhuang, B. Xu, Y. Yan. Universal dependence of hydrogen oxidation and evolution reaction activity of platinum-group metals on pH and hydrogen binding energy. Science Advances 2016, 2(3).

Metal-Free Mesoporous SiO2 Nanorods as a Highly Efficient Catalyst for the Baeyer–Villiger Oxidation under Mild Conditions

The development of efficient and environmentally friendly catalysts for oxidative reaction is of great importance in applied catalysis. In this work, a simple and environmentally benign approach for highly selective preparation of e-caprolactone by oxidation of cyclohexanone has been carried out, which employed metal-free mesoporous silica (mSiO2) nanorods as catalyst under atmospheric pressure. The metal-free silica catalyst was applied for the first time in the Baeyer–Villiger (B–V) oxidation reaction. It showed efficient catalytic performance for the B–V oxidation of various cyclic ketones and aliphatic ketones with O2/benzaldehyde as oxidant. The catalyst could be easily separated from the reaction system by filtration and reused several times without significance loss of activity. Moreover, electron paramagnetic resonance (EPR) spectra of the reaction were obtained, indicating the existence of benzoyloxyl radical. The mechanism study of the reaction demonstrated that the super large surface area dilu...

Microkinetic Modeling of Homogeneous and Gold Nanoparticle-Catalyzed Oxidation of Cyclooctene

Small gold nanoparticles (AuNPs) have recently shown potential to act as a catalyst for oxidation reactions mediated by free radicals, with their role postulated to be facilitating hydrogen abstraction by gold superoxo species and/or activation of hydroperoxides. Cyclooctene oxidation using molecular oxygen as the oxidant at 373 K showed high selectivity to the epoxide product, cyclooctene oxide, with either tert-butyl hydroperoxide as an initiator or in the presence of small AuNPs (5–8 atoms). While previous studies have investigated the mechanism leading to high epoxide selectivity using density functional theory, a full microkinetic model was developed in this work using automated network generation to determine the relative contributions of elementary reactions and the role of AuNPs. A cycle of radical addition of peroxy and alkoxy radicals with subsequent epoxidation reactions can justify the observed activity and selectivity to epoxide at multiple temperatures and initiator concentrations. The alcoh...

High-performance Platinum-free oxygen reduction reaction and hydrogen oxidation reaction catalyst in polymer electrolyte membrane fuel cell

The integration of polymer electrolyte membrane fuel cell (PEMFC) stack into vehicles necessitates the replacement of high-priced platinum (Pt)-based electrocatalyst, which contributes to about 45% of the cost of the stack. The implementation of high-performance and durable Pt metal-free catalyst for both oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) could significantly enable large-scale commercialization of fuel cell–powered vehicles. Towards this goal, a simple, scalable, single-step synthesis method was adopted to develop palladium-cobalt alloy supported on nitrogen-doped reduced graphene oxide (Pd3Co/NG) nanocomposite. Rotating ring-disk electrode (RRDE) studies for the electrochemical activity towards ORR indicates that ORR proceeds via nearly four-electron mechanism. Besides, the mass activity of Pd3Co/NG shows an enhancement of 1.6 times compared to that of Pd/NG. The full fuel cell measurements were carried out using Pd3Co/NG at the anode, cathode in conjunction with Pt/C and simultaneously at both anode and cathode. A maximum power density of 68 mW/cm2 is accomplished from the simultaneous use of Pd3Co/NG as both anode and cathode electrocatalyst with individual loading of 0.5 mg/cm2 at 60 °C without any backpressure. To the best of our knowledge, the present study is the first of its kind of a fully non-Pt based PEM full cell.

Sub-5nm monodispersed PdCu nanosphere with enhanced catalytic activity towards ethylene glycol electrooxidation

Although explosive studies on pursuing high-performance direct fuel cells in the past decades have been carried out, the lack of cost-efficient anode catalysts for oxidation reaction of clean fuel remain a harsh challenge that greatly hinder the development of fuel cell technology. For addressing these issues, we herein combined both of the morphological and component advantages to engineer an advanced monodispersed PdCu nanoalloy catalysts with ultrasmall diameter. A series of electrochemical measurements have revealed that the resulted monodispersed Pd1Cu1 nanospheres can meet the requirement of high surface area with a high electrochemically active surface area (EASA) values of 31.1 m2 g−1, which is 4.06 times higher than that of commercial Pd/C. Similarly, the newly-prepared monodispersed PdCu nanospheres also exhibited much higher mass activity and durability than single-phase Pd and commercial Pd/C towards ethylene glycol electrooxidation in the alkaline media. This work may open a new way for maximizing the electrocatalytic performances by combining the advantages of well-dispersed property and extremely small size.

3D flower-like hierarchical NiCo2O4architecture on carbon cloth fibers as an anode catalyst for high-performance, durable direct urea fuel cells

A 3D NiCo2O4hierarchical architecture composed of interlaced and self-stacked 2D nanoflakes is realized as a urea oxidation reaction catalyst for the generation of green energy in direct urea fuel cells.

Directing a Non-Heme Iron(III)-Hydroperoxide Species on a Trifurcated Reactivity Pathway.

The reactivity of [FeIII (tpena)]2+ (tpena=N,N,N'-tris(2-pyridylmethyl)ethylenediamine-N'-acetate) as a catalyst for oxidation reactions depends on its ratio to the terminal oxidant H2 O2 and presence or absence of sacrificial substrates. The outcome can be switched between: 1) catalysed H2 O2 disproportionation, 2) selective catalytic oxidation of methanol or benzyl alcohol to the corresponding aldehyde, or 3) oxidative decomposition of the tpena ligand. A common mechanism is proposed involving homolytic O-O cleavage in the detected transient purple low-spin (S=1/2 ) [(tpenaH)FeIII O-OH]2+ . The resultant iron(IV) oxo and hydroxyl radical both participate in controllable hydrogen-atom transfer (HAT) reactions. Consistent with the presence of a weaker σ-donor carboxylate ligand, the most pronounced difference in the spectroscopic properties of [Fe(OOH)(tpenaH)]2+ and its conjugate base, [Fe(OO)(tpenaH)]+ , compared to non-heme iron(III) peroxide analogues supported by neutral multidentate N-only ligands, are slightly blue-shifted maxima of the visible absorption band assigned to ligand-to-metal charge-transfer (LMCT) transitions and, corroborating this, lower FeIII /FeII redox potentials for the pro-catalysts.

Cross-Linked Artificial Enzyme Crystals as Heterogeneous Catalysts for Oxidation Reactions.

Designing systems that merge the advantages of heterogeneous catalysis, enzymology, and molecular catalysis represents the next major goal for sustainable chemistry. Cross-linked enzyme crystals display most of these essential assets (well-designed mesoporous support, protein selectivity, and molecular recognition of substrates). Nevertheless, a lack of reaction diversity, particularly in the field of oxidation, remains a constraint for their increased use in the field. Here, thanks to the design of cross-linked artificial nonheme iron oxygenase crystals, we filled this gap by developing biobased heterogeneous catalysts capable of oxidizing carbon-carbon double bonds. First, reductive O2 activation induces selective oxidative cleavage, revealing the indestructible character of the solid catalyst (at least 30 000 turnover numbers without any loss of activity). Second, the use of 2-electron oxidants allows selective and high-efficiency hydroxychlorination with thousands of turnover numbers. This new technology by far outperforms catalysis using the inorganic complexes alone, or even the artificial enzymes in solution. The combination of easy catalyst synthesis, the improvement of "omic" technologies, and automation of protein crystallization makes this strategy a real opportunity for the future of (bio)catalysis.

Enhanced Fenton, photo-Fenton and peroxidase-like activity and stability over Fe3O4/g-C3N4 nanocomposites

We prepared the Fe3O4/g-C3N4 nanoparticles (NPs) through a simple electrostatic self-assembly method with a 3:97 weight ratio to investigate their Fenton, photo-Fenton and oxidative functionalities besides photocatalytic functionality. We observed an improvement of the Fenton and photo-Fenton activities of the Fe3O4/g-C3N4 nanocomposites. This improvement was attributed to efficient charge transfer between Fe3O4 and g-C3N4 at the heterojunctions, inhibition of electron-hole recombination, a high surface area, and stabilization of Fe3O4 against leaching by the hydrophobic g-C3N4. The obtained NPs showed a higher degradation potential for rhodamine B (RhB) dye than those of Fe3O4 and g-C3N4. As compared to photocatalysis, the efficiency of RhB degradation in the Fenton and photo-Fenton reactions was increased by 20% and 90%, respectively. Additionally, the horseradish peroxidase (HRP) activity of the prepared nanomaterials was studied with 3,3,5,5-tetramethylbenzidinedihydrochloride (TMB) as a substrate. Dopamine oxidation was also examined. Results indicate that Fe3O4/g–C3N4 nanocomposites offers more efficient degradation of RhB dye in a photo-Fenton system compared with regular photocatalytic degradation, which requires a long time. Our study also confirmed that Fe3O4/g-C3N4 nanocomposites can be used as a potential material for mimicking HRP owing to its high affinity for TMB. These findings suggest good potential for applications in biosensing and as a catalyst in oxidation reactions.