Liquid-phase Oxidation Research Articles

Selective Oxidation of p-Cymene over Mesoporous LaCoO3 by Introducing Oxygen Vacancies.

The liquid-phase catalytic oxidation of p-cymene to 4-methylacetophenone is an industrially significant reaction. However, the targeted oxidation of a specific C-H bond of p-cymene is extremely difficult due to there being many branched chains in p-cymene. In here, we designed a simple method to synthesize mesoporous LaCoO3 catalysts with rich oxygen vacancy (Oov) sites. The as-prepared mesoporous LaCoO3 after 550 °C calcination (mLaCoO3) exhibits remarkable catalytic activity for solvent-free oxidation of the p-cymene reaction, with a selectivity of over 80.1% selectivity for 4-methylacetophenone and a conversion of 50.2% for p-cymene (120 °C, 3 MPa). Besides, recycling studies have demonstrated that the mLaCoO3 catalysts can be reused ten times in the aerobic oxidation of the p-cymene reaction without significant catalytic activity reduce. The experimental and characterization results indicated that the mesoporous structure of the catalyst is conducive to the generation of surface Oov, which can properly facilitate ion spread during the catalytic process and afford enough O2 for intermediate species, thus is beneficial for the generation of 4-methylacetophenone. This work demonstrates that the selectivity oxide p-cymene with an O2 employing mLaCoO3 catalyst is highly promising for chemical industrial applications.

Modulating Carbon Fiber Surfaces with Vinyltriethoxysilane Grafting to Enhance Interface Properties of Carbon Fiber/Norbornene-Polyimide Composites.

In this study, vinyltriethoxysilane (TEVS) was introduced onto the surface of carbon fiber using liquid-phase oxidation and impregnation methods to incorporate vinyl groups onto the carbon fiber, thereby enhancing the chemical bonding between the carbon fiber and norbornene-polyimide (PI-NA). Through a systematic study of the hydrolysis conditions and concentration of the TEVS solution, the optimal modification conditions were determined. These conditions were used to graft TEVS onto the surface of oxidized carbon fiber to prepare carbon-fiber-reinforced PI-NA composites (CF/PI-NA). The results show that when carbon fiber was treated with a 0.4 wt% TEVS solution, the interlaminar shear strength (ILSS) of the composites reached 65.12 MPa, and the interfacial shear strength (IFSS) reached 88.58 MPa, representing increases of 27.58% and 35.62%, respectively, compared to the CF/PI-NA composite materials prepared from untreated carbon fiber. It is worth noting that the modification method described in the study is simple and easy to implement, and it has the potential for large-scale continuous production applications.

Liquid phase transformation mechanism of β-caryophyllonic acid initiated by hydroxyl radicals and ozone in atmosphere

β-caryophyllonic acid (BCA), as an important precursor of aqueous secondary organic aerosols (aqSOA), has adverse effects on the atmospheric environment and human health. However, the key atmospheric chemical reaction process in which BCA participates in the formation of aqueous secondary organic aerosols is still unclear. In this study, the reaction mechanism and kinetics of BCA with ·OH and O3 were investigated by quantum chemical calculations. The initiation reactions between BCA and ·OH include addition and H-abstraction reaction pathways, subsequent intermediates will also react with O2, ultimately undergo a cracking reaction to generate small molecular substances. The reaction of BCA with O3 can generate primary ozone oxides and the Criegee Intermediates oIM3, subsequent main reaction products include keto-BCA, as well as other small molecule aqSOA precursors. The entire reaction process increases the O/C ratio of aqSOA in the aqueous phase and generates products of small molecules such as 4-formylpropionic acid, which plays an important role in the formation of aqSOA. At 298K, the transformation rate constants of BCA initiated by ·OH and O3 are 1.47 × 1010 M−1 s−1 and 3.16 × 105 M−1 s−1, respectively, the atmospheric lifetimes of BCA reacting with ·OH range from 0.86 h–5.40 h, while the lifetimes of BCA reacting with O3 range from 0.44 h–10.04 years. This suggests that BCA primarily reacts with ·OH. However, under higher O3 concentrations, its ozonolysis becomes significant, promoting the formation of aqSOA. According to the risk assessment, the toxicity of most transformation products (TPs) gradually decreased, but the residual developmental toxicity could not be ignored. In this paper, the atmospheric liquid phase oxidation mechanisms of sesquiterpene unsaturated derived acid were studied from the microscopic level, which has guiding significance for the formation and transformation of aqSOA in atmosphere.

Study on Ship Exhaust Gas Denitrification Technology Based on Vapor-Phase Oxidation and Liquid-Phase Impingement Absorption

A system combining gas-phase oxidation and liquid-phase collision absorption for removing NO from marine diesel engine exhaust was proposed. This method was the first to utilize different physical states of the same mixed solution to achieve both pre-oxidation and impingement reduction absorption of exhaust gases. During the pre-oxidation stage, a mixture of (NH4)2S2O8 and urea solution was atomized into a spray using an ultrasonic nebulizer to increase the contact area between the oxidant and the exhaust gas, thereby efficiently pre-oxidizing the exhaust gas in the gas phase. In the liquid-phase absorption stage, the (NH4)2S2O8 and urea solution was used in an impingement absorption process, which not only enhanced gas–liquid mass transfer efficiency but also effectively inhibited the formation of nitrates. Experimental results showed that, without increasing the amount of absorbent used, the maximum NO removal efficiency of this method reached 97% (temperature, 343 K; (NH4)2S2O8 concentration, 0.1 mol/L; urea concentration, 1.5 mol/L; NO concentration, 1000 ppm; pH, 7; impinging stream velocity, 15 m/s), compared to 72% using the conventional liquid-phase oxidation absorption method. Additionally, this method required only the addition of a nebulizer and two opposing nozzles to the existing desulfurization tower to achieve simultaneous removal of sulfur and nitrogen oxides from the exhaust gas, with low retrofitting costs making it favorable for practical engineering applications.

Conceptual design of furfural extraction, oxidative upgrading and product recovery: COSMO-RS-based process-level solvent screening

Liquid phase oxidation of furfural using hydrogen peroxide offers a promising route for bio-based C4 furanones and diacids; however, only dilute water-based process designs have been previously suggested that have limited techno-economic potential. In this study, a conceptual process design is presented, where aqueous furfural is extracted using an organic solvent, coupled with peroxide oxidation and product recovery in the presence of the solvent. To address the problem of solvent selection, the COSMO-RS-based solvent screening framework is applied, where quantum mechanics-based thermodynamics are utilized in pinch-based process models. About 2500 solvent candidates were identified as feasible. Focusing on a set of 400 solvent candidates revealed energy consumption values (Qreb,tot/ṁprod recov) between approximately 2 MWh/tonne and 33 MWh/tonne, signifying the potential of the solvent-based process in outperforming the reference aqueous process (49.4 MWh/tonne). The study provides potential solvent candidates and future directions to consider in more costly computational and experimental efforts.

Mesoporous g-C3N4/ZnFe2O4/TCPP nanocomposite for selective liquid-phase oxidation of alcohols to aldehydes under visible light irradiation

This study provides a viable strategy for the production of aromatic benzaldehydes by a three-component magnetic recoverable photocatalyst. The novel photocatalyst was fabricated by modification of Graphitic carbon nitride (g-C3N4) using ZnFe2O4 magnetic nanoparticles and Tetrakis(4-carboxyphenyl)porphyrin (TCPP) and labeled as CFP where C is the carbonic substrate, F shows the magnetic component and P demonstrated TCPP porphyrin. The optimized CFP photocatalyst demonstrated approximately 96 % conversion and 99 % selectivity for the oxidation of benzyl alcohol to benzaldehyde. The photocatalytic reaction carried out in the presence of acetonitrile and H2O2 as solvent and oxidant under LED lamp (15 W) irradiation. The results reveal that the values of conversion and selectivity of various types of benzylic alcohols are attributed to the aromaticity and position of substituents on the benzene ring. The reusability of CFP photocatalyst was investigated up to the fourth cycle, and it revealed any significant loss of photocatalytic oxidation activity, which is related to high structural stability of photocatalyst.

Microwave Solid-Phase Synthesis of Ni-Co Ferrites and their Activities in Liquid-Phase Oxidation of m-Xylene

In this paper, the activity of mono- and di-substituted cobalt and nickel ferrites prepared by microwave solid-phase synthesis was studied in the reaction of liquid-phase oxidation of m-xylene to m-toluic acid. It was established that among the tested samples, the di-substituted ferrites of spinel structure with the composition of Ni0,6Co0,4Fe2O4 have the shortest induction period and the highest initial rate of oxygen absorption. In order to clarify the role of the active surface of the Ni0.6Co0.4Fe2O4 catalyst and the volumetric conversions of m‑xylene in the nucleation stage of primary xylyl radicals, the dependence of the induction period was studied. Furthermore the rate of oxygen absorption was investigated as a function of the time of introduction of the inhibitor into the oxidized m-xylene at different ratios of the total size of the heterogeneous surface to the volume of m‑xylene loaded into the reactor (S/V). The dependence of the selectivity of the process to the targeted product, m-toluic acid, on the specific surface area of the catalyst samples was established and it was shown that selectivity to the by-product, m-methylbenzyl alcohol, increased and selectivity to m-toluic acid decreased in the case of cobalt ferrite with a relatively low specific surface area.It was shown that at the first stage reaction (5–10 min.), ie., in conditions of an as yet undeveloped radical chain reaction, in the presence of disubstituted ferrites of the composition (Ni1–xCoxFe2O4), in comparison with monosubstituted ferrites, a higher initial rate of formation of the primary oxidation product of m-xylene — m-methylbenzylhydroperoxide (main intermediate product obtained during formation of m-toluic acid) is observed. The correlation of the activity of mono- and disubstituted Ni-Co ferrites, in the conditions of developed heterogeneous catalytic conversion of m‑xylene, disubstituted Ni-Co ferrites are also characterized by higher rate of heterogeneous nucleation of free radicals and heterogeneous catalytic conversion of the intermediate product — m-toluic aldehyde to m‑toluic acid. This, in turn, provides a high degree of selectivity for the targeted product with the yield of 79.8 %.

Polyaniline-coated flower-like iron oxide served as anode material for superior-performance lithium-ion batteries

Transition metal oxides applied in anode for lithium-ion batteries are susceptible to particle aggregation during the cycling test, resulting in a low capacity retention during cycling process. In this study, Fe2O3/polyaniline microflowers were prepared via a simple liquid-phase oxidation and calcination process followed by polyaniline coating. Several characterization techniques demonstrated their morphology and chemical composition. When applied in anode for lithium-ion batteries, Fe2O3/polyaniline microflowers exhibit an ultrahigh specific capacity of 1847.1 mAh g−1 over 100 cycles at 0.1 A/g. A high specific capacity of 619.8 mAh g−1 was achieved after 300 cycles at 1.0 A/g. The high performance is mainly due to the polyaniline coating and flower-like microstructures, which can mitigate the volume change, improve the electrical conductivity and cycling stability, and contribute to the rapid Li+ diffusion. This work provides a new route for synthesizing advanced-performance Fe2O3-based anode material.

Forecasting of catalytic activity of phthalimide compounds in the process of liquid-phase aerobic oxidation of alkylaromatic hydrocarbons

The authors calculated the single occupied molecular orbital energies of the substrate radical and the phthalimide catalyst radical by the Hartree-Fock quantum chemical method (PM7). According to the research, low numerical values of ∆Esomo characterise N-hydroxyphthalimide derivatives containing electron-donating substituents in their structure and possess high catalytic activity. Application of such compounds allows ones to intensify essentially the process of alkylaromatic hydrocarbons aerobic liquid-phase oxidation with preservation of feedstock conversion high parameters and selectivity of its hydroperoxide formation. The calculated data are in good agreement with the experimentally obtained data. Hence, the proposed method can be used to evaluate the catalytic activity of phthalimide compounds with respect to a wide range of aromatic hydrocarbons.

Water-soluble arylhydrazone complexes based on Mn(II) and Cu(II) as catalysts for liquid-phase toluene oxidation

Novel hydrosoluble coordination compounds based on arylhydrazones of β-diketones and bearing first row transition metals, namely [Mn(μ-1κO1,2κO2-HL1)2(H2O)2]n (1) and [Cu(κO1O2N-L2)(DEA)] (2; DEA = diethanolamine), were synthesised and characterized. Their structural features were investigated using single crystal X-ray diffraction. The catalytic performance of the complexes was explored for liquid phase oxidation of toluene in homogeneous medium using aqueous tert‑butyl hydroperoxide (TBHP) and hydrogen peroxide (H2O2) as oxidants. Both catalysts demonstrated activity, producing a mixture of benzaldehyde, benzyl alcohol and benzoic acid. Under optimized conditions, in the presence of catalysts 1 and using an aqueous TBHP solution as oxidant, the oxidation of toluene yielded an overall 42.6 % of oxygenated products. Contrary to what has been regularly reported regarding selectivity for benzaldehyde, benzoic acid was the predominant product in this study (71 %).

Liquid phase oxidation of cyclopentanone over metal-free carbon catalysts

Oxidation of cyclopentanone (CPO) was studied over metal-free carbon catalysts in solvent-free conditions. Norit SX plus (900 m2 g−1) and Vulcan XC72 (240 m2 g−1) were used as pristine materials. Catalysts were prepared by activation in nitrogen and by treatment with urea, calcined in nitrogen at 500 °C and 950 °C. SEM, EDX, XPS, X-ray powder diffraction, nitrogen adsorption–desorption isotherms, acid–base titration, FTIR and Raman techniques were used for characterization. Catalytic tests carried out at 0.45 MPa and 80–110 °C enabled to find the best results: 30% selectivity to glutaric acid (GA) and 3% to succinic acid at 25% conversion of CPO, over Vulcan type catalysts. A low activity, selectivity and strong deactivation of Norit type catalysts can be ascribed to a higher specific surface in a disordered arrangement providing a high concentration of unselective catalytic sites. A higher extent of side reactions can yield in higher molar mass products, which stick on the surface and block catalytic sites. Optimum amount of accessible planar domains, represented by graphene and/or graphitic plates with some disorders present in Vulcan type catalysts classified them superior to Norit catalysts. A redox reaction scheme of oxidation of CPO to GA is also proposed.Graphical abstract

Soft-templating synthesis of mesoporous MnSiOx composites as catalytic supports for Pd nanoparticles towards solvent-free oxidation of benzyl alcohol under atmospheric pressure O2

Solvent-free and liquid-phase selective oxidation of aromatic alcohols using O2 as an oxidant is a green strategy for the synthesis of aromatic aldehydes and other carbonyl compounds. Wherein, the design and preparation of heterogeneous catalysts with high activity and selectivity is a hot topic in this process. Herein, a series of manganese oxide-silica (MnSiOx) composites were synthesized using cetyltrimethylammonium bromide as a soft template. During the preparation process, the amounts of tetraethyl orthosilicate and ammonia and the calcination temperature significantly affected the textural properties and Mn cation distributions of MnSiOx. The MnSiOx composites were then employed as catalysts for Pd nanoparticles. In the solvent-free and atmospheric conditions, Pd/MnSiOx materials showed high catalytic conversions of benzyl alcohol (BZA), and the catalytic activity thereof is related to the fractions of Pd0 and Mn3+. As the reaction time and temperature are 4 h and 90 °C, the conversion of BZA (feeding dosage: 4 mL) and the selectivity of benzaldehyde are 64.8 % and 94.9 %, respectively. The catalyst can be reused at least five times without any significant loss of activity. Furthermore, the correlation between physiochemical properties and catalytic activity of Pd/MnSiOx was analyzed.

Study of the kinetic regularities of the process of liquid phase oxidation of sec-butylbenzene in the presence of N-hydroxyphthalimide

Study of the kinetic regularities of the process of liquid phase oxidation of sec-butylbenzene in the presence of N-hydroxyphthalimide

Effect of Ag Addition to Au Catalysts for the Oxidation of 5‐Hydroxymethylfurfural to 2,5‐Furandicarboxylic Acid

AbstractThe addition of Ag to Au nanocatalysts is known to improve several catalytic reduction and oxidation reactions. Until now, bimetallic AuAg catalysts have not been studied in detail in liquid phase oxidation reactions. We investigated the activity, selectivity, and stability of silica supported Au, Ag and AuAg catalysts in the oxidation of 5‐hydroxymethylfurfural (HMF) to 2,5‐furandicarboxylic acid (FDCA), an important reaction to produce bio‐based polymers. We demonstrate that addition of an optimum amount of inactive Ag to the active Au catalyst substantially increases the overall selectivity and yield of the desired FDCA. Interestingly, Ag addition decreased the conversion rate of the reactant HMF to the intermediate HMFCA, but improved (up to 10–20 % Ag addition) much the conversion of the intermediate product to the desired final product. This is probably due to tuning the electronic properties of the nanoparticles to achieve an optimum adsorption strength of the intermediate on the surface of AuAg catalysts. Moreover, particle growth was suppressed by the bimetallic AuAg catalyst, ultimately leading to superior stability compared to its monometallic counterparts.

A new Janus mesh membrane with ultrafast directional water transportation and improved fog collection

Fog collection materials have been intensively investigated and can potentially be used to alleviate freshwater shortages. However, developing highly efficient fog collection materials remains challenging. Requisite improvements in fog collection technology are the ultrafast transportation of captured water and the effective regeneration of fresh regions on the surfaces of fog collection materials. Herein, a novel Janus mesh membrane (JMM) with an alternating hydrophobic–superhydrophilic-patterned hydrophobic surface and asymmetric wettability interface is prepared by a selective liquid-phase surface oxidation strategy. The unique structure and high-contrast wettability of the JMM enable ultrafast directional transportation of tiny water droplets (< 0.1 µL), thereby achieving an excellent water collection efficiency of 15.28 g h−1 cm−2, which is much higher than those of conventional Janus membranes. The JMM functioned as a versatile fog collector and maintained continuous fog collection regardless of the fog flow direction. This study offers a novel approach for preparing innovative fog collection materials and establishes a foundation for developing advanced fog collection systems suitable for diverse applications.

Pollution characteristics and transformation mechanisms of secondary inorganic components during winter heavy pollution in Handan city in 2018–2020

The mechanism of secondary transformation of nitrate and sulfate under different relative humidity (RH), and different atmospheric oxidizing conditions is still controversial. This study focuses on the winter heavy pollution process in Handan city from 2018 to 2020, and the following results were obtained: The average concentration of PM2.5 showed a decreasing trend from year to year, but the SNA (SO42−, NO3− and NH4+) showed an increasing trend from year to year, and the concentration of nitrate exceeded that of sulfate. During the haze formation period from 2018 to 2020, a significant disparity was observed in NO2 and SO2 emissions, with NO2 emissions surpassing those of SO2. Mobile sources were found to contribute more emissions than fixed sources, particularly during the haze persistence period (HP). However, sulfate conversion outweighed nitrate conversion. HighRH and photochemical reactions induced by ozone favored the formation of nitrate and sulfate, which formated heavy haze. When 40% ≤ RH ≤ 70%, atmospheric oxidants (Ox = O3 + NO2) concentration was the highest, nitrogen oxidation ratio (NOR) and sulfur oxidation ratio (SOR) increased rapidly, and nitrate was mainly generated by photochemical reactions during daytime. When RH > 70% and the concentration of Ox was low, RH will weaken the photochemical intensity. Therefore, the liquid-phase oxidation reaction of N2O5 contributed significantly to atmospheric nitrate at night, and the liquid-phase oxidation reaction of sulfate was faster than the gas-phase one. Local emissions contributed significantly to particulate matter pollution during heavy pollution in 2018–2020, and the main sources were secondary conversion, coal combustion, biomass burning, and road dust.

Synthesis and DFT studies of robust heterogeneous Co(III) catalyst for liquid phase oxidation of tetralin

Synthesis and DFT studies of robust heterogeneous Co(III) catalyst for liquid phase oxidation of tetralin

Effect of purification methods on the quality and morphology of plastic waste-derived carbon nanotubes

Recent innovative research efforts on the usage of plastic wastes as a cheap carbon source for carbon nanotubes (CNTs) production have emerged as a low-cost and sustainable means of producing CNTs. However, plastic waste-derived CNTs are rarely used in some purity-sensitive and high-alignment needed applications due to the poor quality of CNTs resulting from the abundance of impurities such as non-crystalline amorphous carbon, metallic nanoparticles, and other impurities. Therefore, purification is a crucial issue to be addressed to fully harness all potential applications of CNTs derived from waste plastic materials. Here, the effect of employing different purification methods on the morphology and purity of waste plastic-derived CNTs was investigated. CNTs were synthesized using waste polypropylene plastic as carbon feedstock via a single-stage catalytic chemical vapour deposition (CVD) technique. As-produced CNTs were purified using liquid-phase oxidation (chemical oxidation in nitric acid), gas-phase oxidation in air, and a combination of both liquid- and gas-phase oxidation methods. The synthesized and purified CNTs were characterized for morphology, purity, surface functional groups, thermal stability, and crystallinity using Transmission electron microscopy (TEM), Raman spectroscopy, Fourier Transform Infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA), and X-ray diffraction (XRD), respectively. Results obtained showed that a combination of both liquid and gas phase oxidation purification techniques resulted in purer, better quality, and less defective CNTs with an IG’/IG value of 0.89 and ID/IG value of 0.86, while chemically treated CNTs (CNT-PC) presented more structurally defective CNTs and shortened nanotubes compared to other investigated treatment methods with an ID/IG value of 0.96. CNTs purified by a multi-step protocol (CNT-PAC) showed the highest weight loss of 72.3% indicating the highest quality and the presence of filamentous carbon. This study confirms that the choice of purification techniques influences the morphology and quality of plastic-derived CNTs.

Cobalt(II) mediated electro-oxidation of toluene and its derivatives

The oxidation of toluene and its derivatives is crucial for the chemical industry. Traditional liquid-phase oxidation technologies require high-temperature and high-pressure conditions, which causes high safety risks and urgently requires alternatives. This article reports an electrochemical oxidation method using cobalt acetate as a mediator, which successfully realizes the mild oxidation of toluene. The method turns toluene into highly active radicals by the electrochemically generated Co(III) from cobalt acetate, which significantly reduces the anodic potential in contrast to the direct electro-oxidation and the other reported mediated oxidation processes. The target products, benzaldehyde and benzoic acid, exhibit high yields at 85 °C as the ratio of AcO- to Co(II) is close to 2 in the homogeneous anhydrous electrolyte. A benzyl radical-centered mechanism for the Co(II) mediated electro-oxidation of toluene is proposed based on the cyclic voltammetry tests and a radical inhibiting experiment. The method has also been successfully applied to the derivatives of toluene.

Preparation of cobalt catalyst supported on perovskite-type oxide and application in liquid-phase selective oxidation reaction

Abstract Cobalt catalyst supported on the perovskite-type oxide sodium tantalate, NaTaO3 (NTO) was prepared by using the hydrothermal method and used in liquid-phase p-xylene oxidation, which led to p-methyl benzyl alcohol, p-tolualdehyde, and p-toluic acid. Investigation showed that the formation of alcohol and aldehyde was a competitive reaction. Further oxidation of the alcohol did not occur. On the other hand, the oxidation of p-tolualdehyde led to the formation of acid. Co-NTO catalyst showed higher selectivity toward the route of p-tolualdehyde than the p-methylbenzyl alcohol compared with the bulk Co3O4.