Oxidative Conversion Research Articles

Urea Enzymolysis‐Induced Ions Replacing: A Promising Strategy for One‐Pot Loading of Core–Shell Heterojunction on 1D Catalyst Support

AbstractEven distribution of core–shell heterojunction on porous catalyst supports is promising to get the super‐catalysts, yet laborious preparation hinders the wide application. A novel strategy of urea enzymolysis‐induced ions replacement is proposed for one‐pot loading of Bi12O17Cl2@Bi48Al2O75 core–shell heterojunction onto porous Al2O3 nanorod (named as Al2O3‐Bi12O17Cl2@Bi48Al2O75). The clever combination of urea enzymolysis and precipitation reactions that consume the ions generated in urea enzymolysis can switch the “on‐off” of urease, and thus allow the precise controlling of the concentration and existence time of the ions, as well as ions replacement. It is the urea enzymolysis‐induced ions replacing strategy that can generate the unique structure of Al2O3‐Bi12O17Cl2@Bi48Al2O75, and it is the distinctive structure that can get the selectivity of 96% benzaldehyde with 90% benzyl alcohol (BA) conversion in the photocatalytic oxidation of BA. The ions replacement, the growth of Al2O3‐Bi12O17Cl2@Bi48Al2O75, and the photocatalytic mechanism are investigated in detail. This work highlights a novel and convenient strategy for one‐pot loading core–shell heterojunction onto porous nanorod support, unveils a fresh biosynthesis of nanomaterials with elaborate structure, and thus paves the way for wide application of elaborate nanomaterials.

Regulatory Mechanisms and Synergistic Enhancement of the Diiron YtfE Protein in Nitric Oxide Reduction.

The diiron-containing YtfE protein in Escherichia coli is pivotal in counteracting nitrosative stress, a critical barrier to bacterial viability. This study delves into the biochemical complexity governing YtfE's conversion of nitric oxide (NO) to nitrous oxide, a key process for alleviating nitrosative stress. Through site-directed mutagenesis, we explored YtfE's molecular structure, with a particular focus on two internal transport tunnels important for its activity. Our findings illuminate Tunnel 1 as the primary conduit for substrate transport, regulated by conformational shifts within the N-terminal domain that enable substrate access to the diiron core in the C-terminal domain. Tunnel 2 emerges as a secondary, supportive route, activated when Tunnel 1 is compromised. This result challenges a previous model of distinct tunnels for substrate entry and product exit, suggesting both tunnels are capable of transporting substrates and products. Our engineering efforts enhanced the role of Tunnel 2, enabling a synergistic operation with Tunnel 1 and tripling YtfE's enzymatic activity compared to its wild-type form. This research not only deepens our understanding of YtfE's regulatory mechanism for NO reduction but also introduces a strategy to amplify its enzymatic efficiency. The outcomes offer new ravenues for modulating bacterial stress responses.

Unraveling Urban NOx Emission Sources in Polluted Arctic Wintertime Using NO2 Nitrogen Isotopes

AbstractNitrogen (N) isotopic fractionation during nitrogen oxides (NOx) cycling and conversion into atmospheric nitrate alters the original N isotopic composition (δ15N) of NOx emissions. Limited quantification of these isotopic effects in urban settings hampers the δ15N‐based identification and apportionment of NOx sources. δ15N of nitrogen dioxide (NO2) measured during winter in downtown Fairbanks, Alaska, displayed a large temporal variability, from −10.2 to 24.1‰. δ15N(NO2) records are found to be driven by equilibrium isotopic fractionation, at a rate in very close agreement with theoretical predictions. This result confirms that N isotopic partitioning between NO and NO2 can be accurately predicted over a wide range of conditions. This represents an important step for inferring NOx emission sources from isotopic composition measurement of reactive nitrogen species. After correcting our δ15N(NO2) measurements for N fractionation effects, a δ15N‐based source apportionment analysis identifies vehicle and space heating oil emissions as the dominant sources of breathing‐level NOx at this urban site. Despite their large NOx emissions, coal‐fired power plants with elevated chimney stacks (>26 m) appear to make a small contribution to surface NOx levels in downtown Fairbanks (likely less than 18% on average). The combined uncertainties of the δ15N of NOx from heating oil combustion and of the influence of low temperatures on the δ15N of NOx emitted by vehicle exhaust prevent a more detailed partitioning of surface NOx sources in Fairbanks.

Universal high-efficiency electrocatalytic olefin epoxidation via a surface-confined radical promotion

Production of epoxides via selective oxidation of olefins affords a fundamental source of key intermediates for the industrial manufacture of diverse chemical stocks and materials. Current oxidation strategy generally works under harsh conditions including high temperature, high pressure, and/or request for potentially hazardous oxidants, leading to substantial challenges in sustainability and energy efficiency. To this end, direct electrocatalytic epoxidation poses as a promising solution to these issues, yet their industrial applications are limited by the low selectivity, low yield, and poor stability of the electrocatalysts. Here we report a universal electrochemical epoxidation approach via a kinetically confined surface radical pathway. High epoxidation efficiency can be achieved under mild working conditions (e.g., >99% selectivity, >80% yield and >80% Faraday efficiency for cyclohexene-to-cyclohexene oxide conversion), which can be extended to broad scope of olefin substrates. The catalytic performance originated from a surface bimolecular (L-H) reaction mechanism involving formation and surface confinement of bromine radicals due to kinetic restriction, which effectively activates inert C=C bonds while avoiding the homogenous radical side reactions. With the use of renewable energy and water as green oxygen source, successful implementation of this approach will pave the way for more sustainable chemical production and manufacturing.

Perfluoroalkyl acid precursor or weakly fluorinated organic compound? A proof of concept for oxidative fractionation of PFAS and organofluorines.

Organofluorine mass balance approaches are increasingly applied to investigate the occurrence of per- and polyfluoroalkyl substances (PFAS) and other organofluorines in environmental samples more comprehensively. Usually, complex samples prevent the identification and quantification of every fluorine-containing molecule. Consequently, large unidentified fractions between fluorine sum parameters such as extractable organic fluorine (EOF) and the sum of quantified analytes are frequently reported. We propose using oxidative conversion to separate (unidentified) weakly fluorinated compounds (e.g., pesticides, pharmaceuticals) from PFAA-precursors (perfluoroalkyl chain lengths ≥ C6). We show with three organofluorine model substances (flufenamic acid, diflufenican, pantoprazole) that CF3-groups or aromatic fluorine can be quantitatively converted to inorganic fluoride and trifluoroacetic acid (TFA) by applying PhotoTOP oxidation (UV/TiO2). The principle of fluorine separation in mixtures is demonstrated by the oxidation of the three weakly fluorinated compounds together with the PFAA-precursor 6:2/6:2 fluorotelomer mercaptoalkyl phosphate diester (FTMAP). After oxidation, the products F- and TFA were separated from PFCAs (> C4) by SPE, and the fractions were analyzed individually. Closed mass balances both with and without the addition of organic matrix were achieved. Eventually, the fluorine balance was verified by total fluorine measurements with combustion ion chromatography (CIC). The proposed methods should be considered a proof of concept to potentially explain unidentified fractions of the EOF, especially if compounds with low fluorine content such as pesticides, pharmaceuticals, and their transformation products contribute largely to the EOF. Future studies are needed to show the applicability to the complexity of environmental samples.

Iron-catalysed cooperative redox mechanism for the simultaneous conversion of nitrous oxide and nitric oxide

Iron-catalysed cooperative redox mechanism for the simultaneous conversion of nitrous oxide and nitric oxide

Nano-MnOx prepared by redox method for toluene oxidation removal from air

Catalytic oxidation is an efficient VOCs removal technology with great potential and development advantages. The key to the oxidative elimination of VOCs lies in the development and application of the catalyst with high efficiency. In this work, the nano-MnOx catalysts were prepared by redox method and the catalytic oxidation performance of toluene was studied. The calcination temperature could effectively change the surface chemical composition and the nano-MnOx catalyst structures, which could effectively regulate the number of active centers on the catalyst surface to improve the adsorption, activation, and oxidation ability of the nano-MnOx catalysts for toluene molecules. The nano-MnOx catalyst dominated by the MnO2 phase, which was prepared at the calcination temperature of 400 °C, had a high specific surface area, developed porosity, abundant reactive oxygen species, and oxygen vacancies. The structural characteristics are conducive to the adsorption, activation, and oxidation of toluene molecules, and thus exhibited excellent toluene catalytic oxidation activity. At the reaction temperature of 140 °C, the toluene oxidation conversion was as high as 99.4 %, and the toluene conversion remained above 96.6 % after experiencing a 690 min stability test.

Insights into the mechanism of enhancing resistance of MnAlOx-Str NH3-SCR catalyst derived from streptomycin waste residue and LDHs

Streptomycin waste residue composited with Layered double hydroxides (LDHs) derived Mn1Al1Ox-Str-2 catalyst was proposed for NH3 selective catalytic reduction (NH3-SCR) denitration technology, which improved the overall catalytic performance. In the wide temperature range of 150-300℃, the preferred Mn1Al1Ox-Str-2 catalyst had Nitrogen oxides (NOx) conversion of exceeded 96%, which was higher than that of the control Mn1Al1Ox and Mn/Al2O3 catalysts. In addition, Mn1Al1Ox-Str-2 catalyst had better resistance to SO2 and/or H2O, as well as good regeneration ability. Various analytical techniques had confirmed that the Mn1Al1Ox-Str-2 catalyst derived from streptomycin residue composite LDHs precursor had better surface properties with more active species, abundant surface oxygen, higher reduction capacity and better adsorption of NOx and NH3. Analytical techniques revealed that the Lewis acid site on the surface of Mn1Al1Ox-Str-2 catalyst was involved in SCR reaction and both the Eley-Rideal mechanism and Langmuir-Hinshelwood mechanism existed simultaneously in the NH3-SCR reaction, and SO2 had a weak effect on the adsorption of reactants with fewer sulfate species formation. This work provided feasible strategies for efficient and stable SCR technology and efficient utilization of streptomycin residue waste resources, which was significant for the design and application of SCR technology in the future.

Influence of water vapor partial pressure on self-healing and oxidation of SiC-dispersed yttrium silicate composites

The self-healing and oxidation behavior of SiC-dispersed Y2Si2O7-Y2SiO5 composites were elucidated under various water vapor partial pressures PH2O. Samples were exposed in a furnace for self-healing experiments at 1100–1300°C and for high-temperature oxidation at 1200–1400°C, both for 1–24 h, under PH2O ranging from 2×104 to 5×104 Pa, while keeping PO2constant at 2×104 Pa. Water vapor promoted the self-healing effectiveness of the composites. A mechanism contributing to the closure of surface cracks was consistent with volume expansion derived from the oxidative conversion of SiC into SiO2 and the outward diffusion of yttrium cations. The formation of the internally oxidized zone signifies oxidation behavior, resulting from the inward diffusion of oxygen ions. Growth of the internally oxidized zone obeys the parabolic pattern. The influence of PH2O on the high-temperature oxidation of SiC/Y2Si2O7-Y2SiO5 is discussed in this study.

Evaluation of 3β-hydroxysteroid dehydrogenase activity using progesterone and androgen receptors-mediated transactivation.

3β-Hydroxysteroid dehydrogenases (3β-HSDs) catalyze the oxidative conversion of delta (5)-ene-3-beta-hydroxy steroids and ketosteroids. Human 3β-HSD type 2 (HSD3B2) is predominantly expressed in gonadal and adrenal steroidogenic cells for producing all classes of active steroid hormones. Mutations in HSD3B2 gene cause a rare form of congenital adrenal hyperplasia with varying degree of salt wasting and incomplete masculinization, resulting from reduced production of corticoids and androgens. Therefore, evaluation of the HSD3B2 enzymatic activity in both pathways for each steroid hormone production is important for accurately understanding and diagnosing this disorder. Using progesterone receptor (PR)- and androgen receptor (AR)-mediated transactivation, we adapted a method that easily evaluates enzymatic activity of HSD3B2 by quantifying the conversion from substrates [pregnenolone (P5) and dehydroepiandrosterone (DHEA)] to (progesterone and androstenedione). HEK293 cells were transduced to express human HSD3B2, and incubated medium containing P5 or DHEA. Depending on the incubation time with HSD3B2-expressing cells, the culture media progressively increased luciferase activities in CV-1 cells, transfected with the PR/AR expression vector and progesterone-/androgen-responsive reporter. Culture media from human and other mammalian HSD3B1-expressing cells also increased the luciferase activities. HEK293 cells expressing various missense mutations in the HSD3B2 gene revealed the potential of this system to evaluate the relationship between the enzymatic activities of mutant proteins and patient phenotype.

Enhanced conversion of a magnetic oxide to metal using induction heating: Application for H2 production

In this study, a C–CoFe2O4 composite is proposed for reduction in an induction heating reactor with a continuous argon flow. An impressive conversion efficiency of 87% is achieved at a maximum temperature of 325 °C in just 8 min without the need for vacuum. The impact of the molar ratio of metal oxide to reducing agent (acetylacetone) is also examined. Results indicate that a 1:1 ratio favours the reduction towards cobalt and iron monoxides, while a 1:3 ratio yields a 31% metal phase. The highest conversion (87%) is seen with a 1:17 ratio, indicating the need for excess reducing agent for effective conversion of CoFe2O4 oxide. The molar ratio influences the induction heating temperature, with the 1:17 ratio having a lower temperature of 325 °C compared to 450 °C for other ratios. These operating temperatures (≤450 °C) are significantly lower than those reported in the literature for carbothermal reduction in an induction reactor (>1700 °C), which often requires vacuum and very high temperatures for high conversion efficiency. The proposed process offers advantages such as high conversion efficiency, fast processing, and simpler operational conditions. Additionally, the metallic phases produced are utilized for H2 production in thermochemical water splitting, showcasing these materials potential for energy generation applications.

Incorporation of Mg/Al metal oxide into ionic liquids for CO2 capture and conversion into cyclic carbonate under solvent-free conditions: effect of coordination ability, recyclability, and catalytic study

The direct conversion of carbon dioxide (CO2) and propylene oxide (PO) into propylene carbonate (PC) offers a green way to utilize anthropogenic CO2. However, this reaction is limited by low conversion of PO and harsh reaction conditions. In this study, we solve this problem using ionic liquids (ILs)/metal oxide composites (ILs@MAO). The catalytic activity of MAO-500 (500 = annealing temperature) is poor evidenced by its low conversion of PO (24.94%). However, ILs@MAO-500 has a high conversion of PO (97.54%) under similar reaction conditions (2 h at 1.5 MPa CO2 pressure, 90 oC, and 0.85 g catalyst). The ILs consist of imidazolium cation with weak coordinated [NTf2]- anion leading to outward movement of anion resulting in the formation of “heterodinuclear complex”. This complex generates an amorphous-crystalline intermediate with balanced acid-base sites that activate PO and stabilize the catalytic intermediate. The high PO conversion is theorized to be primarily due to in large part the abundant reactive sites in the ILs that are covalently immobilized on the MAO-500 carrier. Furthermore, even after multiple recycling, ILs@MAO-500 remains stable and exhibits high yield and selectivity. The proposed solvent-free catalytic system is mild, kinetically fast, and naturally safe for coupling CO2 and PO into PC synthesis.

Dual Modification Strategy: Passivation Layer and Cocatalyst on Hematite for Improved Photoelectrochemical Water Oxidation.

α-Fe2O3 is a very attractive photoanode for photoelectrochemical (PEC) water decomposition. However, its short diffusion length, poor conductivity, and fast charge-carrier recombination severely limit device efficiency. Here, coloading an Al2O3 passivation layer and a CoOx cocatalyst onto Ti-doped α-Fe2O3 was carried out to promote PEC water oxidation by improving charge separation and transfer at the electrode/electrolyte interface and inhibiting photocarrier recombination. The optimized Ti:Fe2O3/Al2O3/CoOx photoanode shows a large photocurrent density of 1.41 mA cm-2 at 1.23 V vs reversible hydrogen electrode, which is 47 times greater than that of a pristine Ti:Fe2O3 photoanode. The dual modifications with a combined passivation layer and cocatalyst on the photoanode verify a valuable way for solar energy conversion in PEC water oxidation.

Comparing low-temperature NH3-SCR activity, operating temperature window and kinetic properties of the Mn-Fe-Nb/TiO2 catalysts prepared by different methods

In order to overcome the shortcomings of traditional V-based catalysts, such as poor low-temperature activity, narrow temperature window, and toxicity. Therefore, the Mn-Fe-Nb/TiO2 catalysts were prepared using impregnation (IM), citric acid complexation (CA), co-precipitation (CP), hydrothermal synthesis (HY), and sol–gel (SG) methods to develop novel NH3 selective catalytic reduction (NH3-SCR) catalysts with excellent low-temperature activity, a wide temperature window, and environmental friendliness. Their NH3-SCR catalytic activity was evaluated, followed by a detailed analysis of their morphology, structure, specific surface area, chemical state, redox properties, acidity, and interactions using X-ray diffraction (XRD), Bruaner-Emmet-Teller (BET), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), NH3 temperature-programmed desorption (NH3-TPD), and Fourier transform infrared spectroscopy (FTIR) techniques. The 5Mn-7Fe-4Nb/TiO2-SG catalyst, prepared via sol–gel, exhibited the highest denitrification (de-NOx) activity and the widest operating temperature window, achieving over 80% Nitric oxide (NO) conversion at 180–350 °C and a peak conversion of 97% at 250 °C. The XRD, BET, SEM, and HR-TEM characterization results showed that the catalyst prepared using the sol–gel method had the smallest particles, the highest specific surface area, and the greatest dispersion. XPS and NH3-TPD results revealed that the catalyst prepared using the sol–gel method possessed the highest surface adsorbed oxygen (Oα) content and the largest number of acidic sites. H2-TPR and FTIR analyses indicated that the catalyst prepared using the sol–gel method enhanced the reduction capacity and possessed the strongest interaction forces among support-active-promoter components. Steady-state kinetic tests confirmed that in the NH3-SCR reaction, the rate-determining step was the adsorption activation of NO on the catalyst surface. The sol–gel method reduced the activation energy for de-NOx reactions, enhancing the low-temperature activity of the catalyst.

Novel 3D printed bioactive SiC orthopedic screw promotes bone growth associated activities by macrophages, neurons, and osteoblasts.

Ceramic additive manufacturing currently relies on binders or high-energy lasers, each with limitations affecting final product quality and suitability for medical applications. To address these challenges, our laboratory has devised a surface activation technique for ceramic particles that eliminates the necessity for polymer binders or high-energy lasers in ceramic additive manufacturing. We utilized this method to 3D print bioactive SiC orthopedic screws and evaluated their properties. The study's findings reveal that chemical oxidation of SiC activated its surface, enabling 3D printing of orthopedic screws in a binder jet printer. Post-processing impregnation with NaOH and/or NH4OH strengthened the scaffold by promoting silica crystallization or partial conversion of silicon oxide into silicon nitride. The silica surface of the SiC 3D printed orthopedic screws facilitated osteoblast and neuron adhesion and extensive axon synthesis. The silicate ions released from the 3D printed SiC screws favorably modulated macrophage immune responses toward an M1 phenotype as indicated by the inhibition of TNFα secretions and of reactive oxygen species (ROS) expression along with the promotion of IL6R shedding. In contrast, under the same experimental conditions, Ti ions released from Ti6Al4V discs promoted macrophage TNFα secretion and ROS expression. In vivo tests demonstrated direct bone deposition on the SiC scaffold and a strong interfacial bond between the implanted SiC and bone. Immunostaining showed innervation, mineralization, and vascularization of the newly formed bone at the interface with SiC. Taken altogether, the 3D printed SiC orthopedic screws foster a favorable environment for wound healing and bone regeneration. The novel 3D printing method, based on ceramic surface activation represents a significant advancement in ceramic additive manufacturing and is applicable to a wide variety of materials.

Reducing CO[formula omitted] emissions, energy consumption, and decarbonization costs in manganese production by integrating fuel-assisted solid oxide electrolysis cells in two-stage oxide reduction

Manganese is one of the most consumed metals due to its use in iron and steel making, which generates between 7%–9% of all CO2 emissions produced globally per annum. For the first time, this work explores the potential of a novel process concept to reduce CO2 emissions, energy consumption, and decarbonization costs in manganese production, which involves integrating fuel-assisted solid oxide electrolysis cells (FASOECs) in a two-stage scheme for the reduction of raw manganese ores. In this scheme, higher oxides that are present in raw manganese ores (MnO2, Mn2O3, Mn3O4) are pre-reduced using CO, yielding manganese monoxide (MnO) that is further reduced to Mn in a submerged arc furnace (SAF) using coke and electricity. In the proposed FASOEC integration concept, off-gas from the manganese ores after pre-reduction (a mixture of H2, CO, and CO2) is supplied to the FASOECs’ anode as fuel, in order to produce high-purity H2 in the cathode that is directed to the first stage of manganese reduction. H2 has enhanced reaction kinetics for reducing higher manganese oxides in comparison to CO; therefore, integrating FASOECs can improve manganese oxide conversion rates during pre-reduction, resulting in lower consumption rates of coke and energy in the SAF. The off-gas supplied to the FASOECs’ anode also lowers the amount of energy required for H2 production in the cathode (can also generate electricity, simultaneously) and produces anode exhaust gas containing only CO2 and steam. Since steam can be easily condensed from this stream, the integration of FASOECs also enables efficient decarbonization of the manganese production process, thus eliminating the need for a designated CO2 capture system. The techno-economic analysis performed herein demonstrates that directing the full supply of off-gas produced by the SAF to the FASOECs’ anode at 800 °C reduces the overall energy consumption of manganese production by up to 18% in comparison to conventional processes. This results in decarbonization cost reductions by as much as 3%–15% and a corresponding decarbonization price range of $4-32 per ton of manganese product for plant capacities of 50 and 200 kt, respectively.

Facile microwave synthesis of various-shaped magnetite/ reduced graphene oxide heterostructures and their magnetization properties

Heterostructures of magnetite (Fe3O4) nanoparticles and reduced graphene oxide (RGO) sheets are very common composite materials for different applications such as catalysis, energy storage, and biomedicine. Developing methods for the facile control of the size and shape of both freestanding Fe3O4 nanoparticles and those anchored onto RGO sheets is in demand. Herein, we report on the rapid and facile microwave synthesis (MWS) of Fe3O4 nanoparticles and Fe3O4/RGO with various sizes and shapes using the oleylamine (OAm)/oleic acid (OAc) ligand pair. The solvothermal synthesis using microwave irradiation (MWI) resulted in the concurrent conversion of graphene oxide (GO) into RGO and the in-situ formation of various-shaped Fe3O4 on RGO sheets. Freestanding Fe3O4 nanoparticles of various shapes were prepared using MWS for comparison. The morphological, structural, and surface properties of the samples were studied using different characterization techniques. The magnetization properties of the prepared samples were determined using a vibrating sample magnetometer. Various-shaped standalone and RGO-supported Fe3O4 nanoparticles including nanospheres, nanocubes, and nanotriangles were synthesized via MWI at 1000 W for 20 min by changing the ratios of the iron precursor and the OAm/OAc ligand pair. Interestingly, the MWI using OAm/OAc ligand pair of a molar ratio of 3:4 resulted in the in-situ formation of large hexagonal Fe3O4/RGO. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results confirm the crystallinity and spinel structure of the prepared Fe3O4 samples and prove the concurrent conversion of GO into RGO with assemblies of Fe3O4 nanoparticles. The magnetization measurements further emphasized the role of size and shape in affecting the magnetic properties of Fe3O4 and Fe3O4/RGO heterostructures. The results identify the qualities of the prepared samples and prove the MWS as a facile one-pot method for the preparation of Fe3O4 and Fe3O4/RGO heterostructures.

1O2 and Base Assisted Oxidative Conversion of β-Enaminoesters to α-Acyloxy-β-ketoesters under Visible Light Irradiation.

Singlet oxygen (1O2) and base assisted conversion of β-enaminoesters to α-acyloxy-β-ketoesters is demonstrated under visible light irradiation. The reaction involves formation of an imine intermediate via ene-type pathway initiated by 1O2 followed by base promoted dimerization and hydrolysis steps. The method is mild, environmentally friendly, requires air as the oxidant, and gives the products in moderate to high yields.

Methane capture, utilization, and sequestration technology based on biological ectoine production using Methylotuvimicrobium alcaliphilum 20Z

Methanotroph-based CH4 conversion technology is a promising alternative to conventional CH4 utilization methods that rely on energy-intensive CO2 capture processes. In this study, we introduce a novel CH4 capture, utilization, and sequestration (MCUS) technology as a proof-of-concept for eco-friendly CH4 conversion that is applicable to various methanotroph strains. We validated this hypothesis by evaluating ectoine production in Methylotuvimicrobium alcaliphilum 20Z. Cultivation experiments were conducted using pure O2 pulse injection to facilitate the separation of the CO2 generated during CH4 oxidation by concentrating it. To verify the MCUS concept systematically, we performed a model-based process analysis. The operational strategies for the reactors were developed using experiment-based kinetics and reactor models, followed by the design of a rigorous process flow diagram. Economic and environmental impact analyses were conducted to compare MCUS with air-based cultures and existing oxidative CH4 conversion technologies. The key advantage of MCUS is its significantly lower CO2 emissions (0.71 kg-CO2 eq/kg-CH4) than oxidative CH4 utilization (>2.75 kg-CO2 eq/kg-CH4). Moreover, the net present value per CH4 molecule was estimated at 0.7 $/kg-CH4, substantially higher than existing oxidative conversion methods (0.03 $/kg-CH4). Additionally, compared with air-based cultivation, the MCUS process exhibits superior economic and environmental performances. We used methanotrophs for CH4 “capture” and “utilization,” effectively leveraging “sequestration” to convert emissions into pure CO2. The proposed MCUS technology holds promise for practical applications of methanotrophs in producing various high-value-added products, emphasizing eco-friendly approaches.

Recent Advances in the Biosynthesis of Mid- and Long-Chain Dicarboxylic Acids Using Terminally Oxidizing Unconventional Yeasts.

As high-performance monomers for the manufacture of polyamide materials, mid- and long-chain dicarboxylic acids (DCAi, i ≥ 6) have received extensive attention from researchers. Biosynthesis is gradually replacing chemical synthesis due to its outstanding advantages in the industrial production of mid- and long-chain dicarboxylic acids, which is mostly achieved by using the strong terminal oxidation ability of nonmodel microorganisms such as Candida tropicalis to oxidize hydrophobic substrates such as alkanes. Here, we first summarize the metabolic pathways of oxidative alkane conversion into dicarboxylic acid by terminally oxidizing unconventional yeasts and the corresponding metabolic engineering strategies. Then, we summarize the research progress on new dicarboxylic acid production processes. Finally, the future development directions in the biosynthesis of mid- and long-chain dicarboxylic acids are prospected from synthetic biology and bioprocess engineering, which can also provide a reference for the synthesis of other biobased chemicals and biomaterials.