Clean Oxidation Research Articles

The Azobis(isobutyronitrile)-Promoted Oxidative Radical α-Cyanation of Imine under Atmospheric O2.

Herein, we report an azobis(isobutyronitrile) (AIBN)-promoted radical α-cyanation of in situ formed imine under atmospheric O2. This oxidative radical addition (ORA) procedure proceeds with the sequential homocleavage of AIBN, extrusion of N2, and capture of O2 toward an O-centered radical, which is converted to a cyano radical by β-scission. Then, the insertion of the cyano radical into the imine C═N bond forms an aminyl radical, leading to α-cyano imine after 1,2-hydrogen atom transfer (HAT) and H abstraction. Such a transition-metal-free procedure features mild reaction conditions and a broad substrate scope, employing molecular O2 as a clean terminal oxidant.

CaCO3-activited N-doped diatom biochar for the degradation of tetracycline

In this study, a N-doped diatom biochar (DBC) was prepared by one-step pyrolysis, where CaCO3 formed by marine diatom-mediated calcification was employed as an activator. Due to the activation effect of CaCO3, the specific surface area of the obtained DBC increased by more than 10 times, and the nitrogen presented as pyrrolic nitrogen (58.9%), pyridinic nitrogen (29.7%), and graphitic nitrogen (11.4%) in the DBC. In addition, the effects of important parameters and co-existing ions on the catalytic decomposition of tetracycline (TC) by DBC were investigated by using TC as a typical pollutant and PDS as an oxidant. The DBC/PDS system exhibited high activity over a broad pH range. Through radical scavenging experiments, electron spin resonance, and electrochemical results analysis, it was found that the degradation of TC in the system included both radical and nonradical pathways, and the most dominant reactive species was 1O2. Furthermore, the surficial reactive complexes formed by PDS on the catalysts also played an important role in attacking the adsorbed TC molecules. This study proposes an eco-friendly and economical technique to construct a clean advanced oxidation process capable of treating TC wastewater by utilizing the native biomass of diatom as a metal-free and efficient biochar catalyst while simultaneously reducing the use of chemical reagents.

Synthesis, characterization, and a comparative study on the catalytic activity of the functionalized magnetic nanoparticles for the green oxidation of sulfides

AbstractIn the following research, meso‐tetrakis(4‐carboxyphenyl)porphyrinatomanganese (III) acetate (MnTCPP(OAc)) was immobilized onto the surface of two functionalized magnetic nanoparticles (MNPs) with different linker length via amide bond (Fe3O4@SiO2‐NH2‐MnTCPP(OAc) (A1) and Fe3O4@SiO2‐NHCO‐NH2‐MnTCPP(OAc) (A2)). The prepared catalysts were characterized by standard methods such as: atomic absorption spectroscopy (AAS), Ultra violet‐visible (UV‐Vis), Fourier‐transform infrared (FT‐IR), vibrating sample magnetometry (VSM), field emission scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM) techniques and also the effect of the length of the linker on the catalytic activity of supported magnetic nanohybrids was investigated. The prepared magnetic nano‐catalysts with different linker lengths were participated in a comparative study of the clean oxidation of sulfides with urea hydrogen peroxide (UHP) in ethanol. The higher catalytic activity, selectivity and also reusability were achieved in the presence of the catalyst with longer linker length (A2) at ambient temperature. Moreover, the turnover number (TON) of catalytic reactions using A2 as catalyst was highly enough to consider the catalyst as an efficient material to oxidize various sulfides. Both A1 and A2 catalysts simply have accomplished 5 runs of recycling without significant decrease in the catalytic activity.

Application of clean oxidation technology using H2O2 for simultaneous removal of sulfur and organic substances in the Bayer process

The harmful effects of sulfur and organic substances pose constraints on the green and sustainable development of the Bayer process for alumina production. This research aims to develop a method that utilizes H2O2 to remove sulfur and organic substances during the digestion stage of bauxite, based on the mineralogical investigation of sulfur and organic substance. The extent of removal of S2− and total organic carbon reached 95.6% and 68.0%, respectively, under most suitable conditions of 12% H2O2 dosage, temperature of 533 K, and duration of 80 min. Based on thermodynamic calculations, it is suggested that S2− is oxidized to SO42−. Additionally, the free radical reaction mechanism of organic substances in H2O2 wet oxidation of Bayer liquor is proposed. The results confirm that this method does not introduce any impurities and does not have any impact on the digestion efficiency of alumina and the Bayer process.

Visible‐Light‐Mediated Oxygenation of Benzylic C(Sp3)−H Bonds and Oxidation of Aryl Carbinols using Non‐Noble Transition Metal Photoredox Catalyst

AbstractA simple and efficient methodology for the selective oxygenation of benzylic C(sp3)−H bond and oxidation of primary and secondary alcohols using non‐noble photoredox copper catalyst under visible light irradiation is described. Notably, non‐noble copper photoredox catalysts were found to be good for the oxidation reactions when compared to various commercially available photoredox catalysts employed in the present methodology. In addition, oxygen as clean oxidant at room temperature and compatible for both the oxygenation and oxidation reactions. A wide range of carbonyl compounds bearing both electron rich and electron deficient substituents was synthesized in moderate to excellent yields under milder and environmentally friendly conditions. Also, a thorough investigation was carried out to understand the mechanism of both oxidation reactions.

Polygonal mesopores microflower catalysts for the catalytic oxidation of 2-nitro-4-methylsulfonyltoluene to 2-nitro-4-methylsulfonylbenzoic acid in a continuous-flow microreactor

The development of efficient systems for the catalytic oxidation of 2-nitro-4-methylsulfonyltoluene (NMST) to 2-nitro-4-methylsulfonyl benzoic acid (NMSBA) with atmospheric air or molecular oxygen in alkaline medium presents a significant challenge for the chemical industry. Here, we report the synthesis of FeOOH/Fe3O4/MOF polygonal mesopores microflower templated from a MIL-88B(Fe) at room temperature, which exposes polygonal mesopores with atomistic edge steps and lattice defects. The obtained FeOOH/Fe3O4/MOF catalyst was adsorbed onto glass beads and then introduced into the microchannel reactor. In the alkaline environment, oxygen was used as oxidant to catalyze the oxidation of NMST to NMSBA, showing impressive performance. This sustainable system utilizes oxygen as a clean oxidant in an inexpensive and environmentally friendly NaOH/methanol mixture. The position and type of substituent critically affect the products. Additionally, this sustainable protocol enabled gram-scale preparation of carboxylic acid and benzyl alcohol derivatives with high chemoselectivities. Finally, the reactions can be conducted in a pressure reactor, which can conserve oxygen and prevent solvent loss. Moreover, compared with the traditional batch reactor, the self-built microchannel reactor can accelerate the reaction rate, shorten the reaction time and enhance the selectivity of catalytic oxidation reactions. This approach contributes to environmental protection and holds potential for industrial applications.

A thermodynamic perspective on electrode poisoning in solid oxide fuel cells

A critical challenge to the commercialization of clean and high-efficiency solid oxide fuel cell (SOFC) technology is the insufficient stack lifespan caused by a variety of degradation mechanisms, which are associated with cell components and chemical feedstocks. Cell components related degradation refers to thermal/chemical/electrochemical deterioration of cell materials under operating conditions, whereas the latter regards impurities in feedstocks of oxidant (air) and reductant (fuel). This article provides a thermodynamic perspective on the understanding of the impurities-induced degradation mechanisms in SOFCs. The discussion focuses on using thermodynamic analysis to elucidate poisoning mechanisms in cathodes by impurity species such as Cr, CO2, H2O, and SO2 and in the anode by species such as S (or H2S), SiO2, and P2 (or PH3). The author hopes the presented fundamental insights can provide a theoretical foundation for searching for better technical solutions to address the critical degradation challenges.

Recent advances in photothermal catalysis: Coupling hydrogen evolution and organic conversion

Photothermal catalysis, as a green and sustainable technology, has attracted increasing attention in the fields of clean energy and green organic synthesis. Integrating photothermal catalysis with solar-driven hydrogen production and organic synthetic chemistry has become a promising strategy for sustainable energy generation with great research and practical value. In this review, we present an overview of the background of solar-driven photothermal catalytic reactions, introduce the fundamental principles of photocatalysis, thermal catalysis, and photothermal reduction of hydrogen coupled with selective oxidation of organic compounds, and summarize the recent advances in photothermal semiconductor catalysts such as carbon-based materials, titanium-based materials, noble metal composites, and metal sulfides. We also highlight the recent advances in the application of these catalysts in photothermal catalytic water splitting for hydrogen generation and selective oxidation of organic compounds. Finally, we address the challenges and opportunities faced by solar-drive photothermal catalysts in the synergism of photocatalytic hydrogen production and selective oxidation of organic compounds. The aim is to provide guiding insights for the rational design of this dual-function catalytic system, offering a green pathway for the development of clean energy and selective oxidation in organic synthesis.

Ru/O2-Catalyzed Oxidative C-H Activation/Alkyne Annulation Using Quinoline-Functionalized NHC as a Directing and Functionalizable Group.

The ruthenium/O2-catalyzed oxidative annulation reaction of imidazo[1,5-a]quinolin-2-ium salts with alkynes via N-heterocyclic carbene-directed C-H activation to obtain π-conjugated fused imidazo[1,5-a]quinolin-2-ium derivatives is reported. Molecular oxygen has been explored as an economic and clean oxidant and an alternative to metal oxidants. The current protocol exhibits a wide range of substrate scope including bioactive (±)-α-tocopherol derivatives. Moreover, most of the annulated products show strong fluorescence properties, indicating their potential for making new light-emitting materials.

Visible-Light-Promoted Cascade Coupling of 2-Isocyanonaphthalenes with Elemental Sulfur and Amines to Construct Naphtho[2,1-d]thiazol-2-Amines.

A visible-light-induced strategy has been explored for the synthesis of naphtho[2,1-d]thiazol-2-amines through ortho-C-H sulfuration of 2-isocyanonaphthalenes with elemental sulfur and amines under external photocatalyst-free conditions. This three-component reaction, which utilizes elemental sulfur as the odorless sulfur source, molecular oxygen as the clean oxidant, and visible light as the clean energy source, provides a mild and efficient approach to construct a series of naphtho[2,1-d]thiazol-2-amines. Preliminary mechanistic studies indicated that visible-light-promoted photoexcitation of reaction intermediates consisting of thioureas and DBU might be involved in this transformation.

Metal- and base-free, aerobic photoredox catalysis with riboflavin to synthesize 2-substituted benzothiazoles.

Sustainable approaches for the synthesis of 2-substituted benzothiazoles are sought after for their use in organic chemistry, bioorganic chemistry, and industrial applications. Here, we described a visible light-driven photoredox catalytic cyclization of thioanilides to afford 2-substituted benzothiazoles using riboflavin as a photocatalyst, where oxygen is used as a clean oxidant and ethanol as a greener solvent. These results provide a new photochemical route for environmentally benign synthesis.

Copper-containing POM-based hybrid P2Mo22V4Cu4 nanocluster as heterogeneous catalyst for the light-driven hydroxylation of benzene to phenol.

The current traditional phenol production process has many shortcomings, and the efficient and clean photocatalytic one-step oxidation to phenol is gradually attracting attention. Heteropolyacids (PMo10V2) with high-density Lewis acid active sites and excellent photoelectron transfer ability are ideal choices for catalytic reactions. In this study, a copper-modified isolated dimeric hybrid nanocluster, [Cu(pyim)2]2[Cu(pyim)2(P2MoVI20MoV2VIV4O82)]2·(H2O) (pyim = [2-(pyridin-2-yl)imidazole]), was synthesized by a convenient hydrothermal method. The structural analysis demonstrated that the compound was composed of metal-organic complexes containing pyim ligands, Keggin-type heteropolyacids, and transition metal copper ions. Remarkably, this not only solves the difficulty that the heteropolymeric acid cannot be recovered by dissolving in the solvent but also introduces the copper atom as a second active center. The catalyst exhibited a benzene conversion of 15.6% and a selectivity of 85.2% in a mixed solution of acetonitrile and acetic acid under optimal reaction conditions. After four catalytic cycles, the PXRD pattern proved that the catalyst was still stable. This study provides a good idea for photocatalytic reactions and other environmental applications.

Fast ammonium sulfate salt assisted roasting for selectively recycling degraded LiFePO4 cathode

Selectively recycling degraded cathode materials from retired lithium-ion battery is an efficient approach which could shorten recovery processes and reduce energy consumption and carbon emissions. Herein, we propose a fast ammonium sulfate ((NH4)2SO4) salt roasting method to extract Li and recycle FePO4 from commerical LiFePO4 cathode materials. Compared with the traditional hydrometallurgy recovery process, (NH4)2SO4 assisted roasting achieved the fast delithiation of LiFePO4 within 5 min at 300 °C, and converted LiFePO4 to FePO4 in air atmosphere. Almost 98% of Li was converted to soluble Li2SO4, and air acted as a clean and cheap oxidant. TG-DSC analysis in different atmospheres indicated that the whole reaction mainly consisted of two steps: (NH4)2SO4 firstly decomposed to NH4HSO4 and (NH4)2S2O7, and then the LiFePO4 reacted with O2, (NH4)2SO4 and (NH4)2S2O7 at ∼300 °C. Thermodynamic analysis also supported the above reaction mechanism. In a word, (NH4)2SO4 salt assisted roasting provides an effective approach to selectively extracting Li from polyanionic cathode materials.

Efficient bisphenol A removal by a photocatalyst-enzyme hybrid system: Horseradish peroxidase integrated with carbon vacancy-modified carbon nitride nanosheets

Peroxidase-based treatment that uses H2O2 as the clean oxidant appears promising for the removal of aqueous phenolic endocrine disrupting chemicals (EDCs). However, oxidative degradation of active heme species at high H2O2 concentrations leads to irreversible enzyme inactivation. The method of combining photocatalysis and enzyme biocatalysis could alleviate the issue by photocatalytic in-situ H2O2 production. In this study, we constructed a photocatalyst-enzyme hybrid system that integrated the horseradish peroxidase with carbon vacancy-modified carbon nitride nanosheets (HRP@ACNNs). Attributed to the modified carbon nitride, the HRP@ACNNs exhibited higher substrate affinity and comparable catalytic efficiency compared to free HRP. This photocatalyst-enzyme hybrid system could offer H2O2 continuously to sustain enzymatic catalysis without enzyme inactivation as well as stabilize the enzyme. The bisphenol A (BPA) removal experiments further confirmed the effectiveness in treating phenolic EDCs of the prepared HRP@ACNNs.

S-Scheme Heterojunction Photocatalyst for Photocatalytic H2O2 Production: A Review

Hydrogen peroxide (H2O2) is a clean and mild oxidant that is receiving increasing attention. The photocatalytic H2O2 production process utilizes solar energy as an energy source and H2O and O2 as material sources, making it a safe and sustainable process. However, the high recombination rate of photogenerated carriers and the low utilization of visible light limit the photocatalytic production of H2O2. S-scheme heterojunctions can significantly reduce the recombination rate of photogenerated electron–hole pairs and retain a high reduction and oxidation capacity due to the presence of an internal electric field. Therefore, it is necessary to develop S-scheme heterojunction photocatalysts with simple preparation methods and high performance. After a brief introduction of the basic principles and advantages of photocatalytic H2O2 production and S-scheme heterojunctions, this review focuses on the design and application of S-scheme heterojunction photocatalysts in photocatalytic H2O2 production. This paper concludes with a challenge and prospect of the application of S-scheme heterojunction photocatalysts in photocatalytic H2O2 production.

Poisoning of automotive methane oxidation catalysts by silicon compounds

Biomethane production offers a viable option to meet the growing demands of renewable energy sources in the transportation sector. However, biomethane contains trace amounts of impurities, such as siloxanes, that can potentially hinder the methane oxidation catalyst performance and lead to excessive greenhouse gas emissions. To investigate this potential problem, the commercial methane oxidation catalysts were poisoned in a laboratory setup with two common siloxanes found in biomethane and with their combustion product, silica. The performances of the clean and poisoned methane oxidation catalysts were measured under realistic lean-burn conditions, after which the catalyst structural changes were determined using XRD, BET and CO chemisorption. The results revealed two different possible poisoning mechanisms. First, both tested siloxanes poisoned the catalysts by migrating selectively on top of the active metal sites and became combusted to form amorphous silica. This caused the methane oxidation performance to drop rapidly with relatively small amounts of siloxane used. In contrast, a significantly higher dose of silica was required to produce a similar poisoning effect because its poisoning mechanism is based on nonselective deposition and physical blocking of the catalyst surface.

Mo@PANI-catalyzed oxidative deoximation reaction

Deoximation is an important transformation in synthetic industry. It can be employed in protection, characterization and purification of the carbonyls, and in the synthesis of ketones from non-carbonyl molecules. In the field, oxidative deoximation reaction can utilize the driving force caused by the oxidation process so that the reaction can occur under relatively mild conditions. Recently, we designed and prepared polyaniline-supported molybdenum (Mo@PANI) just by immersing PANI into the EtOH/H2O solution of MoCl5. The material was successfully applied as the efficient catalyst for oxidative deoximation reactions, which were performed in ethanol using H2O2 as the clean oxidant. The substrate scope of the reaction was wide. It could be applied on heterocycle-containing substrates, making this protocol preferable for pharmaceutical intermediate synthesis. Since Mo is a necessary trace element for both animals and plants, this method is environment-friendly and is suitable for large-scale preparation. This work as the first example of Mo-catalyzed oxidative deoximation reaction may inspire novel ideas for both catalyst design and synthetic process development.

Acid/base-co-catalyzed cyclization of ketones with o-amino-benzylamines: Direct synthesis of quinoline compounds

A novel acid/base-co-catalyzed tandem cyclization of various ketones with o-amino-benzylamines employing molecular oxygen as the clean oxidant has been described. The reaction provides an efficient and general strategy for the construction of fused N-heterocyclic compounds, such as dihydrobenzo[c]acridines, indeno[1,2-b]quinolines, dihydro-5H-benzo[6,7]cyclohepta[1,2-b]- quinolines and quinolones in a single step. The broad scope and the use of oxygen as the sole oxidant make this transformation an attractive approach for the synthesis of the above mentioned scaffolds.

Controlling the surface silanol density in capillary columns and planar silicon via the self-limiting, gas-phase deposition of tris(dimethylamino)methylsilane, and quantification of surface silanols after silanization by low energy ion scattering

Surface silanols (Si-OH) play a vital role on fused silica surfaces in chromatography. Here, we used an atmospheric-pressure, gas-phase reactor to modify the inner surface of a gas chromatography, fused silica capillary column (0.53 mm ID) with a small, reactive silane (tris(dimethylamino)methylsilane, TDMAMS). The deposition of TDMAMS on planar witness samples around the capillary was confirmed with X-ray photoelectron spectroscopy (XPS), ex situ spectroscopic ellipsometry (SE), and wetting. The number of surface silanols on unmodified and TDMAMS-modified native oxide-terminated silicon were quantified by tagging with dimethylzinc (DMZ) via atomic layer deposition (ALD) and counting the resulting zinc atoms with high sensitivity-low energy ion scattering (HS-LEIS). A bare, clean native oxide – terminated silicon wafer has 3.66 OH/nm2, which agrees with density functional theory (DFT) calculations from the literature. After TDMAMS modification of native oxide-terminated silicon, the number of surface silanols decreases by a factor of ca. 10 (to 0.31 OH/nm2). Intermediate surface testing (IST) was used to characterize the surface activities of functionalized capillaries. It suggested a significant deactivation/passivation of the capillary with some surface silanols remaining; the modified capillary shows significant deactivation compared to the native/unmodified fused silica tubing. We believe that this methodology for determining the number of residual silanols on silanized fused silica will be enabling for chromatography.

Performance evaluation of a solar nano-photocatalytic reactor for wastewater treatment applications: Reaction kinetics, CFD, and scale-up perspectives

The solar-driven photocatalytic process, as a clean and efficient advanced oxidation process (AOP), is widely operated in wastewater treatment applications. In the present work, a solar nano photocatalytic reactor is designed, manufactured, and tested under different operating conditions. The irradiation-dependence reaction kinetics is studied in a batch operation process. A comprehensive computational fluid dynamics (CFD) model taking into account realistic solar flux distribution is developed and validated using experimental data. Finally, the reactor scaling-up analysis for higher treatment capacities is performed with the aim of the design of industrial-scale solar photocatalytic reactors. The research results indicate that when the initial dye concentration is increased from 5 to 175 mg/L, the period required to achieve 95% pollutant removal in 20 L solution and 10 mg/L photocatalyst concentration boosts up to 2.2 times. When the photocatalyst concentration in the solution is increased from 5 to 20 mg/L, the time required to achieve 95% total removal is reduced to 35.7%. For the photocatalyst concentration of 75 mg/L compared to 20 mg/L, the time required for 95% degradation increases up to 16.7%. To treat 90% of the total pollutant in a 50 mg/L dye solution with an initial volume of 5 m3 and using 20 mg/L photocatalyst concentration under 11 h operation with an average solar irradiation intensity of 750.46 W/m2, a solar reactor with a surface area of 50.45 m2 is required, while for 10 m3 wastewater sample and the same conditions and 95% pollutant removal, the collector area is obtained to be 121.36 m2. A horizontal solar reactor compared to its optimal tilt angle can reduce the treatment capacity up to 55%.