Selective Oxidation Reactions Research Articles

Green synthesis of cobalt oxide nanoparticles (Co3O4NPs): Characterization and green light-driven photocatalytic aerobic oxidation of alkyl and aryl sulfides to the corresponding sulfoxides

In recent years, cobalt oxide nanoparticles (Co3O4NPs) have garnered significant attention due to their unique properties and wide range of applications, particularly in catalysis and environmental remediation. This study focuses on the green synthesis of Co3O4NPs using garlic extract as a bio-reducing and stabilizing agent, marking the first instance of employing this eco-friendly and cost-effective method. The synthesized nanoparticles were characterized using various techniques including SEM, EDX, FTIR, XRD, UV–Vis DRS, and BET analysis, revealing their spherical morphology, elemental composition, surface area, and optical properties. The primary application investigated was the photocatalytic aerobic oxidation of alkyl and aryl sulfides to sulfoxides under visible green light irradiation. The study meticulously optimized the reaction conditions, evaluating the effects of different solvents, light sources, and catalyst dosages. The optimal conditions were found to be a MeCN:H2O (5:1) solvent system, green LED light (535 nm), and 10 mg of Co3O4NPs catalyst with the highest TON of 12.5. Under these conditions, the catalyst demonstrated high efficiency, achieving up to 95% yield of sulfoxides with various substrates. Furthermore, the reusability of the Co3O4NPs was assessed through multiple catalytic cycles, showing excellent stability and consistent performance. Mechanistic studies indicated that the photocatalytic activity involves the generation of reactive oxygen species (ROS) such as superoxide anion radicals (O2.-) and singlet oxygen (1O2), with both holes and electrons playing crucial roles in the oxidation process. This research highlights the potential of green synthesized Co3O4NPs as effective and sustainable photocatalysts for selective oxidation reactions, offering a promising approach for environmentally benign chemical processes. The findings pave the way for further exploration of bio-derived catalysts in various industrial applications, promoting greener and more sustainable practices in chemical synthesis.

Investigation of the Properties of Unsaturated Allyl Alcohol and its Oxidation Reaction Products

Abstract Organic substances in which the -OH group is directly attached to the carbon atom are called alcohols. Unsaturated alcohols are obtained by replacing the hydrogen of ethylene or acetylene-type compounds with a hydroxyl group. Allyl alcohol, the first representative of the class of unsaturated alcohols, contains oxygen. Allyl alcohol is used in optical resins, protective glasses, paints and coatings and polymer cross-linking agents, as well as in the production of pharmaceuticals, organic chemicals, plastics, herbicides, and pesticides. In organic chemistry, alcohols can be oxidized to aldehydes, ketones, carboxylic acids, and esters that carry a higher oxidation state of carbon. Therefore, the selective oxidation of alcohols is an important issue. The properties and selective oxidation reaction of allyl alcohol were investigated in the presented work.

Synthesis and catalytic application of nanostructured metal oxides and phosphates.

The design and development of new high-performance catalysts is one of the most important and challenging issues to achieve sustainable chemical and energy production. This Feature Article describes the synthesis of nanostructured metal oxides and phosphates mainly based on earth-abundant metals and their thermocatalytic application to selective oxidation and acid-base reactions. A simple and versatile methodology for the control of nanostructures based on crystalline complex oxides and phosphates with diverse structures and compositions is proposed as another approach to catalyst design. Herein, two unique and verstile methods for the synthesis of metal oxide and phosphate nanostructures are introduced; an amino acid-aided method for metal oxides and phosphates and a precursor crystallization method for porous manganese oxides. Nanomaterials based on perovskite oxides, manganese oxides, and metal phosphates can function as effective heterogeneous catalysts for selective aerobic oxidation, biomass conversion, direct methane conversion, one-pot synthesis, acid-base reactions, and water electrolysis. Furthermore, the structure-activity relationship is clarified based on experimental and computational approaches, and the influence of oxygen vacancy formation, concerted activation of molecules, and the redox/acid-base properties of the outermost surface are discussed. The proposed methodology for nanostructure control would be useful not only for the design and understanding of the complexity of metal oxide catalysts, but also for the development of innovative catalysts.

1O2‐Mediated Selective Oxidation of 5‐hydroxymethylfurfural to 2,5‐diformylfuran by Ag/Ag3PO4 under Visible Light Irradiation

AbstractThe synthesis of 2,5‐diformylfuran (DFF) through photocatalytic oxidation of 5‐hydroxymethylfurfural (HMF) is an attractive approach. In this manuscript, a photocatalytic selective oxidation strategy for HMF was developed, using Ag/Ag3PO4 as the photocatalyst and O2 as the oxidizing agent. The prepared catalyst was characterized systematically by SEM, XRD, XPS, UV‐Vis, PL spectra, and so on. In contrast to previous photocatalytic oxidation strategies for HMF conversion, this catalytic system could efficiently generate 1O2 without other reactive oxygen species (ROS) under visible light irradiation. DFF would be obtained with about 90 % selectivity. Moreover, the exclusive formation of 1O2 was linked to the more positive conduction band potential (+0.90 eV) of Ag/Ag3PO4, confirmed by an array of characterization techniques. Additionally, the stability of the catalyst was assessed through cyclic testing and analyses including XRD, and XPS. Nonetheless, this catalytic system could potentially serve as a robust platform for various selective oxidation reactions in the future, due to its exclusive presence of 1O2 without the involvement of other ROS.

Designing TiO2 Nanotubular Arrays with Au-CoOx Core-Shell Nanoparticles for Enhanced Photoelectrochemical Methanol and Lignin Oxidation.

One-dimensional (1D) ordered TiO2 nanotubes exhibit exceptional charge transfer capabilities, making them suitable candidates for constructing visible-light-active photoanodes in selective PEC oxidation reactions. Herein, we employed a facile and easily scalable electrochemical method to fabricate Au-CoOx-deposited ordered TiO2 nanotubular array photoanodes. The improved visible light absorption capacity of TiO2-Au-CoOx, with unhampered 1D channels and the controlled integration of Au between TiO2 and CoOx, along with their synergistic interaction, have been identified as the most promising strategy for enhanced PEC performance, as evidenced by an IPCE of 3.7% at 450 nm. Furthermore, the robust interfacial charge transfer pathway from CoOx to the TiO2 surface via the Au mediator promotes the migration of photogenerated electrons and enables the accumulation of holes on the surface of CoOx. These holes are then efficiently utilized by oxidants such as methanol or lignin to generate value-added products, highlighting the potential of this system for advanced PEC applications.

Synthesis Of Ce/Cu/Nb Catalysts, by the One-Step Polymerization Method, Applied in the Selective Oxidation Reaction of Acetonitrile

Objective: The objective of this study is to investigate the catalytic capacity of cerium, copper and niobium oxide catalysts in the oxidation reaction of acetonitrile, in order to test the catalytic behavior, conversion and selectivity of the catalysts; evaluate the different proportions of niobium used (0, 15, 30, 50 and 75% m.m) and compare the catalytic performance of the synthesized materials with other studies present in the literature. Method: The catalysts were synthesized using the one-step polymerization method and were characterized using XRD and H2-TPR techniques. Then, they were applied in the acetonitrile oxidation reaction to be evaluated for conversion and selectivity. Results and Discussion: The results obtained revealed that the catalysts played a significant role in the proposed reaction, obtaining good conversion and selectivity values, including the production of N2 as the majority. Research Implications: Considering that the oxidation of acetonitrile generates polluting gases from nitrogen compounds, the research presents a method that produces an extremely low quantity of these pollutants. This method ensures better product quality, reduces energy consumption due to the lower reaction temperature and uses cheaper and more viable catalysts. Originality/Value: This study contributes to the literature by being based on compounds not yet used together as catalysts and also for the proposed reaction. The relevance of the use of the catalyst is demonstrated through the results obtained, such as high conversions and selectivities to desirable products.

In-situ fabrication of defect rich Cu2+1O on electrodeposited Cu cone arrays for promoting electrocatalytic anode hydrogen production

The low-potential formaldehyde oxidation reaction (FOR) is a significant replacement for oxygen evolution reaction, as FOR can couple with the cathode hydrogen evolution reaction (HER) to obtain a bipolar H2 production system with an extra low cell voltage. Cu-based electrocatalysts offer cost advantages in FOR but suffer from poor intrinsic activity and stability. Herein, a novel defect rich CF-Cu@Cu2+1O/Cu pinecone-shaped array electrocatalyst is fabricated by in-situ solution immersion of electrodeposited Cu cone arrays on foam for efficient and stable formaldehyde selective oxidation reaction to co-produce hydrogen and valuable formate. Benefitting from the partially mixed Cu2+1O in metallic copper and concomitant production of defect rich oxygen vacancies, only 0.04 VRHE is required for electrocatalytic FOR at 100 mA·cm−2 under alkaline conditions. FOR current density of CF-Cu@Cu2+1O/Cu electrode exhibits 2.35 times than that of CF-Cu (144 mA·cm−2) and 77 times than that of copper foam (4.4 mA·cm−2) at 0.5 VRHE. Moreover, the special pinecone-shaped structure is constructed to modify Cu-based catalysts with substantially enhanced stability. A FOR-HER co-electrolysis device of CF-Cu@Cu2+1O/Cu(+)||Pt/C(−) can achieve bipolar H2 production with an approaching 200 % Faradaic efficiency, requiring an extremely low electrical energy consumption of only ∼ 0.35 kWh per m3 of H2 and potential of 0.291 V at 100 mA·cm−2 at room temperature.

Enhancing acidity of Ru/Ce/ZrO2 bifunctional catalysts for promoting N2 selectivity in selective catalytic oxidation of NH3

To solve the problem of low N2 selectivity of Ru/Ce/ZrO2 (R/C/Z) catalysts in NH3 selective catalytic oxidation (NH3-SCO) reaction, herein ZrO2 supports were treated with sulfuric acid and its effects on NH3-SCO performance were investigated systematically. The results showed that Ru/Ce/ZrO2-10S (R/C/Z-10S) catalyst, in which the mass ratio of sulfuric acid to ZrO2 was 10 %, exhibited N2 selectivity of 95.7 % at 350 °C, that was significantly higher than R/C/Z catalyst (57.8 %). NH3-TPD tests indicated that sulfate treatment of ZrO2 supports in R/C/Z catalysts led to more abundant acidic sites on catalyst surface, which was in favor of enhancing NH3 adsorption capacity remarkably. But when mass ratio of sulfuric acid to ZrO2 increased up to 20 %, an aggregation of metal oxides on the surface of R/C/Z-20S catalyst could be observed clearly, which might impose an adverse impact on NH3-SCO performance. In-situ DRIFTS results revealed that, compared to R/C/Z catalyst, there were much more Brönsted acid sites on the surface of R/C/Z-10S catalyst, and the corresponding NH3 species on acidic sites could be consumed quickly in intermediate reactions. More importantly, amide (-NH2) species rather than imide (-NH) and nitrosyl (-HNO) species, were the majority on the surface of R/C/Z-10S catalyst, implying that there might be a suppressing effect on further dehydrogenation of -NH2 species into -NH species owning to sulfate treatment of ZrO2 supports in R/C/Z catalysts. Therefore, internal selective catalytic reduction (i-SCR) mechanism rather than -NH mechanism played a vital role in NH3-SCO reaction over R/C/Z-10S catalyst.

Selective Oxidation of Benzo[d]isothiazol-3(2H)-Ones Enabled by Selectfluor.

A metal-free and Selectfluor-mediated selective oxidation reaction of benzo[d]isothiazol-3(2H)-ones in aqueous media is presented. This novel strategy provides a facile, green, and efficient approach to access important benzo[d]isothiazol-3(2H)-one-1-oxides with excellent yields and high tolerance to various functional groups. Furthermore, the purification of benzoisothiazol-3-one-1-oxides does not rely on column chromatography. Moreover, the preparation of saccharine derivatives has been achieved through sequential, double oxidation reactions in a one-pot aqueous media.

Improving the Electrochemical Glycerol-to-Glycerate Conversion at Pd Sites via the Interfacial Hydroxyl Immigrated from Ni Sites.

The electrochemical conversion of glycerol into high-value chemicals through the selective glycerol oxidation reaction (GOR) holds importance in utilizing the surplus platform chemical component of glycerol. Nevertheless, it is still very limited in producing three-carbon chain (C3) chemicals, especially glyceric acid/glycerate, through the direct oxidation of its primary hydroxyl group. Herein, Pd microstructure electrodeposited on the Ni foam support (Pd/NF) is designed and fabricated to achieve a highly efficient GOR, exhibiting a superior current density of ca. 120 mA cm-2 at 0.8 V vs. reversible hydrogen electrode (RHE), and high selectivity of glycerate at ca. 70%. The Faradaic efficiency of C3 chemicals from GOR can still be maintained at ca. 80% after 20 continuous electrolysis runs, and the conversion rate of glycerol can reach 95% after 10-h electrolysis. It is also clarified that the dual-component interfaces constructed by the adjacent Pd and Ni sites are responsible for this highly efficient GOR. Specifically, Ni sites can effectively strengthen the generative capacity of the active adsorbed hydroxyl (OHad) species, which can steadily immigrate to the Pd sites, so that the surface adsorbed glycerol species are quickly oxidized into C3 chemicals, rather than breaking the C-C bond of glycerol; thus, neither form the C2/C1 species. This study may yield fresh perspectives on the electrocatalytic conversion of glycerol into high-value C3 chemicals, such as glyceric acid/glycerate.

Study of Mesoporous Zr-TiO2 Catalyst with Rich Oxygen Vacancies for N-Methylmorpholine Oxidation to N-Methylmorpholine-N-oxide.

A series of Zr-TiO2 catalysts were prepared using a facile sol-gel method and were used for N-methylmorpholine (NMM) oxidation to N-methylmorpholine-N-oxide (NMMO). The structure features of Zr-TiO2 catalysts were studied in detail through a variety of characterization methods, such as XRD, SEM, N2 adsorption-desorption isotherms, XPS, EPR, and O2-TPD. As-obtained 5%Zr-TiO2 catalysts had superior catalytic performance and stability with a 97.6% NMMO yield at 40 °C, which related to Zr doping, a higher surface area, more oxygen vacancies, and oxygen chemisorption on the catalytic surface. This work provides an efficient preparation strategy of TiO2-based catalysts for selective oxidation reactions by a facile method.

Oxidation of Ethylene Glycol into Valuable Chemical Using BiVO4 Photoanode

Introduction Plastic photoreforming using photocatalysts is a solar-powered technology that facilitates the generation of hydrogen (H2) from water while simultaneously breaking down plastic waste into valuable organic products. While the focus in the past few decades has predominantly centered on enhancing the H2 production efficiency, recent attention has shifted towards selective plastic oxidation reactions (U. Nwosu, et al. Renew. Sust. Energ. Rev. , 2021, 148, 111266). However, the investigation of effective cocatalysts for selective oxidation of plastic compounds has not been well studied.The photoelectrochemical (PEC) system offers a promising approach by segregating the anodic and cathodic processes, thereby enabling a more concentrated focus on the oxidation reaction in the design of reactions. In this study, we evaluate the BiVO4 photoanode modified with various cocatalysts, for example, cobalt phosphate (Co-Pi) for the oxidation of ethylene glycol (EG), a crucial component in the formation of polyethylene terephthalate (PET). Additionally, we introduce acetonitrile (MeCN) into the reactant mixture to suppress the oxygen evolution reaction (OER), which otherwise competes with the ethylene glycol oxidation reaction (EGOR), creating a more conducive reaction environment for enhanced efficiency. Materials and Methods The BiVO4 photoanode on fluorine doped tin oxide (FTO) glass was fabricated as previously reported (V. Andrei, et al. Adv. Energy Mater , 2018, 8, 1801403). Briefly,BiOI precursor was electrochemically deposited on the FTO glass and then drop-casted a vanadyl acetylacetonate [VO(acac)2] solution onto the surface and heated at 723 K for 60 min. The deposition of the Co-Pi cocatalyst onto BiVO4 was achieved by photoassisted electrodeposition method. The obtained photoanodes were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). PEC measurements were carried out using a three-electrode configuration under simulated solar irradiation (100 mW cm− 2, AM 1.5G). The experiments were performed in various solutions containing 1 M EG: 0.5 M Na2SO4 in H2O, 0.1 M NaClO4 in MeCN, and the mixed solution of MeCN and H2O. Product analysis was performed using proton nuclear magnetic resonance (1H NMR). Results and discussion According to the XRD and SEM results, the formation of nanoporous BiVO4 film on FTO glass was confirmed. To assess the PEC performance for EGOR using BiVO4 electrode, we carried out the experiments under conditions with and without the EG substrate (Figure (a)). With the addition of EG, a notable shift of the onset potential from 0.6 VRHE to 0.5 VRHE was observed. In addition, the photocurrent density at 1.2 VRHE increased from 0.67 mA/cm2 to 0.92 mA/cm2. This result indicates that EGOR is more favorable on the BiVO4 surface compared to OER. The Co-Pi cocatalyst deposition on the BiVO4 notably increased the current under both conditions, with and without the EG substrate. Although Co-Pi is commonly recognized for its catalytic role in OER, our experiment surprisingly revealed its positive impact on EG performance as well. The Co-Pi/BiVO4 photoanode exhibited a negative shift of the onset potential to 0.3 VRHE and an enhancement of photocurrent density to 2.04 mA/cm2 at 1.2 VRHE for EGOR compared to bare BiVO4. Additionally, the Co-Pi/BiVO4 photoanode showed 16.9% and 2.7% faradaic efficiencies (FE) for formate and glyoxal production, respectively, while bare BiVO4 exhibited 10.6% FE for formate and no glyoxal production.Under aqueous conditions, the FE for EGOR is currently low due to the competition between OER and EGOR. To overcome this challenge and enhance the EGOR efficiency, we introduced MeCN into the aqueous solution because MeCN has higher (more positive) anodic oxidation potential than the aqueous medium (L. M. Reid, et al. Sustainable Energy Fuels , 2018, 2, 1905-1927). In the MeCN-water mixed solution (MeCN:water = 9:1), OER was effectively suppressed to 0.33 mA/cm2, while EGOR was significantly enhanced to 2.50 mA/cm2 at 1.2 VRHE potential (Figure (b)). This MeCN-water mixed solvent created a more favorable environment for EGOR on bare BiVO4, resulting in a notable increase in FE for formate to 19.8% and FE for glyoxal to 13.2%, which represents a 1.87 and 4.89 times improvement, respectively, compared to the pure aqueous condition. Conclusions The deposition of Co-Pi cocatalyst on the BiVO4 film improved the photocurrent density and FE for formate production. Moreover, the introduction of MeCN in the solvent created a more favolable reaction condition for EGOR, suppressing OER and increasing the EGOR activity. Figure 1

(Invited) Theoretical Insights in the Design of Active Sites and Environments to Guide Electrocatalytic Transformations for Sustainable Energy and Chemicals Production

Future strategies for sustainable energy and chemicals production will undoubtedly require the design of electrocatalytic systems that actively and selectively convert wastes such as CO2 emissions and biomass into chemicals and fuels. While enzymes elegantly integrate highly active centers together with adaptive nanoscale environments to selectively control catalytic transformations, they are limited industrially by their durability. The design of robust electrocatalytic materials and systems that can mimic the activity and selectivity of enzymes, however, has been hindered by our understanding of how such transformations proceed over inorganic materials and complex environments. Advances in theory, simulations, spectroscopy and characterization begin to allow us to track the molecular transformations and how they proceed in electrocatalytic systems at specific sites and within particular environments. This information can enable the design of unique surface ensembles and nanoscale environments that can efficiently catalyze specific molecular transformations. Herein we develop and use ab initio methods to examine the influence of anions, cations and solvents in complex electrochemical environments to carry out selective molecular transformations. More specifically, we discuss the electrocatalytic reduction of CO2 and aromatics to valuable chemical and pharmaceutical intermediates. We draw direct analogies between the elementary processes that govern these seemingly different systems. We explore the manipulation of different solvents (ionic liquids and water), electrolytes (effects of anions and cations), pH as well as different metals and electrochemical potential to drive the formation of 3D environments that aid in controlling these transformations. We expand the discussion to selective oxidation reactions and examine the design of mediators to enable the selective C-H bond activation.

(Invited) Tailored Electrochemical Interfaces for Renewable Fuels Production

Tailoring the structure of the electrified interface and the electrocatalytically active sites at the atomic and molecular levels is key to elucidating the design principles to develop advanced materials for sustainable energy conversion and storage. This talk will focus on recent strategies to tune the structure-activity-selectivity relationships for oxygen, carbon dioxide/carbon monoxide and methane electrocatalysis to produce renewable fuels.First, I will present our work toward understanding and tuning the structure-property relations for oxygen evolution for the production of green hydrogen in proton exchange membrane water electrolysers. Then, I will show our model studies on well-defined Cu-based surfaces to understand structure-properties relations for the electrochemcial CO2 reduction reaction. We have investigated the effect of electrolyte, pH, and potential dependence for CO reduction on Cu single crystals as well as methods to evaluate the facet distribution on Cu-based catalysts. Finally, I will discuss some strategies for selective oxidation reactions such as partial oxidation of methane to produce liquid fuels such as methanol.

PVP-assisted in-situ self-assembly hierarchical BiOCl with oxygen vacancies for efficient photocatalytic oxidation of cyclohexane under air in solvent-free conditions

Cyclohexane (CHA) selective oxidation reactions are crucial in designing advanced organic intermediates but suffering from very challenges as the products of KA oil (cyclohexanol and cyclohexanone) are more readily oxidized to CO2. Herein, we report that a polyvinylpyrrolidone (PVP) coating of fluffy self-assembled morphology of BiOCl by nanosheets with exposed {001} facets are synthesized via the solvothermal method. Moreover, the as-synthesized hierarchical BiOCl exhibits a significant presence of in-situ produced oxygen vacancies during photocatalysis, thereby facilitating efficient CHA oxidation to KA oil with air as an oxidant in solvent-free at room temperature. The crystallinity, micromorphology, and electronic structure of BiOCl can be significantly influenced by the concentration of NH4Cl and PVP. In the photocatalytic oxidation, oxygen vacancies act as traps to inhibit electrons and holes recombination and adsorb-activate the oxygen molecule, producing h+ and ·O2− radical to achieve 466.7 μmol of KA oil (340.8 μmol of cyclohexanone and 125.9 μmol of cyclohexanol) with a selectivity of 93.9 %. The ∙OH radicals play a predominant role in the production of CHA-one. After conducting 5 experimental cycles, a consistent yield of 92 % towards KA oil and unchanged selectivity can still be maintained. The excellent photocatalytic performance can be attributed to the enhanced photo-absorption and narrow energy gap, abundant oxygen vacancies, high exposed {001} facets, smaller size and large specific surface area, and efficient electron-hole separation. The present work sheds light on the synergistic effect of PVP coating and in-situ formed oxygen vacancies on enhancing photocatalytic activity of Bi-based materials.

Regulating Reactive Oxygen Intermediates of Fe–N–C SAzyme via Second‐Shell Coordination for Selective Aerobic Oxidation Reactions

Reactive oxygen species (ROS) regulation for single‐atom nanozymes (SAzymes), e.g., Fe–N–C, is a key scientific issue that determines the activity, selectivity, and stability of aerobic reaction. However, the poor understanding of ROS formation mechanism on SAzymes greatly hampers their wider deployment. Herein, inspired by cytochromes P450 affording bound ROS intermediates in O2 activation, we report Fe–N–C containing the same FeN4 but with tunable second‐shell coordination can effectively regulate ROS production pathways. Remarkably, compared to the control Fe–N–C sample, the second‐shell sulfur functionalized Fe–N–C delivered a·2.4‐fold increase of oxidase‐like activity via the bound Fe=O intermediate. Conversely, free ROS (•O2‐) release was significantly reduced after functionalization, down to only 17% of that observed for Fe–N–C. The detailed characterizations and theoretical calculations revealed that the second‐shell sulfur functionalization significantly altered the electronic structure of FeN4 sites, leading to an increase of electron density at Fermi level. It enhanced the electron transfer from active sites to the key intermediate *OOH, thereby ultimately determining the type of ROS in aerobic oxidation process. The proposed Fe–N–Cs with different second‐shell anion were further applied to three aerobic oxidation reactions with enhanced activity, selectivity, and stability.

Regulating Reactive Oxygen Intermediates of Fe-N-C SAzyme via Second-Shell Coordination for Selective Aerobic Oxidation Reactions.

Reactive oxygen species (ROS) regulation for single-atom nanozymes (SAzymes), e.g., Fe-N-C, is a key scientific issue that determines the activity, selectivity, and stability of aerobic reaction. However, the poor understanding of ROS formation mechanism on SAzymes greatly hampers their wider deployment. Herein, inspired by cytochromes P450 affording bound ROS intermediates in O2 activation, we report Fe-N-C containing the same FeN4 but with tunable second-shell coordination can effectively regulate ROS production pathways. Remarkably, compared to the control Fe-N-C sample, the second-shell sulfur functionalized Fe-N-C delivered a 2.4-fold increase of oxidase-like activity via the bound Fe=O intermediate. Conversely, free ROS (⋅O2 -) release was significantly reduced after functionalization, down to only 17 % of that observed for Fe-N-C. The detailed characterizations and theoretical calculations revealed that the second-shell sulfur functionalization significantly altered the electronic structure of FeN4 sites, leading to an increase of electron density at Fermi level. It enhanced the electron transfer from active sites to the key intermediate *OOH, thereby ultimately determining the type of ROS in aerobic oxidation process. The proposed Fe-N-Cs with different second-shell anion were further applied to three aerobic oxidation reactions with enhanced activity, selectivity, and stability.

Supported copper nanoarchitecture for selective ethylbenzene oxidation (EBO) reaction

Copper-based (Cu-NP) uniformly dispersed on various inorganic supports (alumina, silica, titania, and zirconia) were prepared by the reverse microemulsion technique. These nanoparticles were used for the selective oxidation of ethylbenzene (EB) to produce acetophenone (AP) as the main product in the presence of Tert‑butyl hydroperoxide(TBHP) as an oxidant. This study focused on creating Cu-nanoparticles evenly dispersed on alumina using varying Cu-loadings (5 %, 10 %, and 15% wt.) and Brij-35 as the surfactant. The resulting catalytic material was characterized using various physicochemical techniques like XRD, FESEM, HRTEM, XPS and physisorption techniques. Various parametric studies were conducted, such as the effects of temperature, catalyst support, catalyst loading, and TBHP loading to optimize the EB conversions and AP selectivity. Among the various catalyst loadings, 15 % CuO/Al2O3 (15 % of the copper content) nanocomposites showed exceptional performance, with the highest EB conversion rate (99.7 %) and AP selectivity (98.5 %) compared to other nanocomposites. The catalyst's stability and recyclability over four cycles were attributed to the strong copper oxide-alumina interaction. These findings suggest that this nanocomposite material is a promising candidate for catalytic applications, offering high selectivity and consistent EB conversion rates.

Temperature dependence mechanism of high-temperature oxidation of transition metal silicide MoSi2

Transition metal silicides represented by MoSi2 have excellent oxidation resistance and are widely used as high-temperature anti-oxidation coatings in hot end components of power equipment. However, the mechanism of temperature-dependent growth of MoSi2 oxidation products has not been revealed. Therefore, this study investigated the formation characteristics of oxide film and silicide-poor compound on MoSi2 at temperatures of 1000 °C–1550 °C through high-temperature oxidation experiments, combined with microscopic Raman spectroscopy, scanning electron microscope, and x-ray diffraction (XRD) characterizations. The result showed that MoSi2 underwent high-temperature selective oxidation reactions at 1000 °C–1200 °C, forming MoO2 and SiO2 oxide film on the substrate. As the oxidation temperature increased to 1550 °C, after 100 h of oxidation, along with the disappearance of MoO2 and the phase transformation of SiO2, a continuous Mo5Si3 layer with a thickness of approximately 47 μm was formed at the SiO2–MoSi2 interface. Thermodynamics and kinetic calculations further revealed the mechanism of temperature-dependent growth of oxidation products (MoO2 and Mo5Si3) during high-temperature oxidation process of MoSi2. As the temperature increased, the diffusion flux ratio of O and Si decreased, leading to a decrease in oxygen concentration at the interface and promoting the growth of the Mo5Si3 layer. Its thickness is an important indicator for evaluating the oxidation resistance of MoSi2 coatings during service. This study provides experimental and mechanistic insights into the temperature-dependent growth behavior of Mo5Si3 during the high-temperature oxidation of MoSi2 coating, and provides guidance for predicting the service life and improving the oxidation resistance of silicide coatings.

The role of Au and Pd in photocatalytic activation of molecular oxygen: A mechanistic study

Activation of molecular oxygen plays an important role in photocatalytic selective oxidation reactions and complete degradation of organic pollutants. Noble metal cocatalysts are often employed to modulate the activation of oxygen to reach an optimum photocatalytic performance. However, the role of the metal nanoparticles (NPs) still remains unclear and deserves investigation for the design of efficient photocatalysts. Here, Au and Pd NPs are deposited on the TiO2 photocatalyst to study the promotional mechanism of O2 dissociation with the presence of glycerol under irradiation by near-ambient-pressure photoelectron spectroscopy and in-situ spectrometry approaches. While both Au and Pd NPs can dissociate O2 into activated oxygen species, a relatively strong bonds of dissociated oxygen atom is observed on Au NPs than on the Pd NPs. This results in a moderate reduction rate of O2 and eventually favors a mild oxidation reaction process for Au, and a rapid reduction rate of O2 and eventually a deep oxidation reaction process for Pd, respectively.