Liquid-phase Oxidation Research Articles

Interchain-expanded extra-large-pore zeolites.

Stable aluminosilicate zeolites with extra-large pores that areopen through rings of more than 12 tetrahedra could be used to process molecules larger than those currently manageable in zeolite materials. However, until very recently1-3, they proved elusive. In analogy to the interlayer expansion of layered zeolite precursors4,5, we report a strategy that yields thermally and hydrothermally stable silicates by expansion of a one-dimensional silicate chain with an intercalated silylating agent that separates and connects the chains. As a result, zeolites with extra-large pores delimited by 20, 16 and 16 Si tetrahedra along the three crystallographic directions are obtained. The as-made interchain-expanded zeolite contains dangling Si-CH3 groups that, by calcination, connect to each other, resulting in a true, fully connected (except possible defects) three-dimensional zeolite framework with a very low density. Additionally, it features triple four-ring units not seen before in any type of zeolite. The silicate expansion-condensation approach we report may be amenable to further extra-large-pore zeolite formation. Ti can be introduced in this zeolite, leading to a catalyst that isactive in liquid-phase alkene oxidations involving bulky molecules, which shows promise in the industrially relevant clean production of propylene oxide using cumene hydroperoxide as an oxidant.

Tert-butyl hydroperoxide decomposition as a descriptor for liquid-phase hydrocarbon oxidation over transition metal oxide-based catalysts: a screening study

Tert-butyl hydroperoxide decomposition as a descriptor for liquid-phase hydrocarbon oxidation over transition metal oxide-based catalysts: a screening study

Low-temperature aerobic oxidation of alcohols to aldehydes over La1-xKxMnO3 nanofiber tubes: Issues on O2 adsorption and activation

Aerobic oxidation of alcohols to aldehydes is a green and prospective route to synthesize fine chemicals, but the high activation barrier and low solubility in organic solvents of O2 make this technology a challenge. Herein, we report an electrospinning synthesis of K doped LaMnO3 perovskite (La1-xKxMnO3), with nanofiber tube (NFT) structure, for efficient liquid-phase aerobic oxidation of alcohols to aldehydes at low temperature. The NFT structure improves the capacity of material to capture O2, the generated oxygen vacancy, caused by K doping, increases the sites to adsorb O2, and the evolved (110) lattice plane promotes the ability to activate O2. The optimized La0.95K0.05MnO3 shows above 93 % conversion and selectivity, even is conducted at 50 °C, for 3 h, which is the lowest temperature reported for aerobic oxidation of alcohols using noble metal-free catalysts. Simulated calculations suggest that the O-O bond can be automatically ruptured if O2 is adsorbed on the (110) lattice plane of the material.

Liquid phase oxidation enables stable soft carbon anodes for potassium-ion batteries

Soft carbon has been recognized as a promising anode material for potassium-ion batteries (PIBs), due to low cost, high conductivity and low voltage platform. However, their practical application is hampered by slow storage kinetics and unsatisfactory cycle life. In this work, pitch-derived needle coke, a typical soft carbon, was incorporated with oxygenated functional groups through liquid phase oxidation by using H2O2 oxidant. When used as anode materials for PIBs, the oxidized needle coke delivers a high reversible capacity of 322.7 mAh g−1, significantly superior to that of the needle coke (237.9 mAh g−1). The enhanced electrochemical performance can be attributed to the abundant oxygenated functional groups and resultant defects on the surface of oxidized needle coke, which not only serve as extra active sites for potassium storage, but also provide sufficient pathways for K+ migration across the adjacent carbon layers. Moreover, the expanded interlayer spacing derived from H2O2 oxidation facilitates rapid K+ intercalation and deintercalation. This work offers an effective modification strategy for the fabrication of high-performance pitch-based soft carbon anodes for PIBs.Graphical

Streamlined synthesis of iron and cobalt loaded MCM-48: High-performance heterogeneous catalysts for selective liquid-phase oxidation of toluene to benzaldehyde

Hydrothermal synthesis of MCM-48 molecular sieves featuring the incorporation of both iron and cobalt with Si/M ratios of 20, 40 and 80 (where M represents either iron or cobalt) was performed using tetraethyl orthosilicate as the silica source and cetyltrimethylammonium bromide as a template. To gain a comprehensive understanding of the synthesized materials, these were thoroughly characterized using various techniques, including XRD, XPS, UV–Vis (DRS), FT-IR, N2 adsorption-desorption analysis, SEM with EDX, TEM, TGA and NH3-TPD analysis. XRD analysis revealed the presence of well-ordered MCM-48 structure in the metal-incorporated materials, while XPS and UV–Vis DRS confirmed the successful partial incorporation of metal ions precisely in their desired tetrahedral coordination within the framework. To assess their catalytic performance, we studied the activity and selectivity of these catalysts in liquid phase oxidation of toluene using tert-butyl hydroperoxide as the oxidant. Under optimized conditions, employing a 6% (w/w) Fe-MCM-48 (40) catalyst and maintaining a toluene to oxidant molar ratio of 1:3 at 353 K in a solvent-free environment for 8 h, the oxidation reaction resulted in the formation of benzaldehyde (88.1%) as the major product and benzyl alcohol (11.9%) as the minor product.

Liquid-Phase Selective Oxidation of Methane to Methane Oxygenates

Methane is an abundant and relatively clean fossil fuel resource; therefore, its utilization as a chemical feedstock has a major impact on the chemical industry. However, its inert nature makes direct conversion into value-added products difficult under mild conditions. Compared to the gas-phase selective oxidation of methane, there have been several recent advances in the liquid-phase conversion of methane. This review categorizes the reports on the liquid-phase selective oxidation of methane according to the solvent and oxidant used. The advantages and disadvantages of each approach are discussed. High yields of methyl bisulfate as a methanol precursor can be achieved using SO3 in sulfuric acid; however, more attention should be paid to the separation process and overall economic analysis. However, the aqueous-phase selective oxidation of methane with in situ generated H2O2 is quite promising from an environmental point of view, provided that an economical reducing agent can be used. Based on the current state-of-the-art on this topic, directions for future research are proposed.

Microbubble-assisted liquid oxidation for efficient one-step phase decomposition and recovery of V and Cr from vanadium slag

Oxidation roasting is an effective way to recover vanadium (V) and chromium (Cr) from vanadium slag but is severely limited by carbon reduction and energy conservation. Herein, a novel method is proposed employing a microbubble-assisted liquid phase oxidation technique , the recovery efficiencies of V and Cr reached 94.11 % and 80.27 %, respectively. The decomposition and oxidization mechanisms of low-valent V and Cr spinels were investigated. Leaching kinetics analyzes demonstrated that microbubbles effectively enrich hydroxide ions on the solid surface and disrupt diffusion resistance, promoting adequate exposure of spinel. The UV and XPS results revealed that the Cr(VI) proportion increased to 12.30 % and 97.2 %, respectively, in tailings and leachate. More importantly, hydroxyl radicals (·OH) were detected during the leaching process, confirming the performance of the self-catalytic oxidation reaction. These discoveries offer a novel pathway with high oxidation efficiency, low energy consumption, and more environmental friendliness for recycling valuable metals from amphoteric mineral resources.

Enhanced Catalytic Activity of a Copper(II) Metal-Organic Framework Constructed via Semireversible Single-Crystal-to-Single-Crystal Dehydration.

Herein, we present a copper(II) metal-organic framework, [Cu2(btec)(OH2)4]·2H2O (1) [(btec)4- = 1,2,4,5-benzenetetracarboxylate], that undergoes single-crystal-to-single-crystal transformations into two anhydrous phases 2' and 2″ with the chemical formula [Cu2(btec)], triggered by two-step dehydration at 403 and 433 K, respectively. After immersion in water for 3 days at room temperature, 2' transformed into [Cu2(btec)(OH2)] (3), while both 2' and 2″ took 1 week to revert to 1. Dynamic vapor sorption studies validated water-induced reversible structural transformations at 70% relative humidity (RH). According to single-crystal X-ray diffraction (SC-XRD), the local coordination geometry of the Cu2+ ion in 2' changed from a saturated octahedron to a coordinatively unsaturated square-based pyramid in 3, manifested by changes in color and dimensionality. From a topological point of view, all of the scaffolds show a binodal (3,6)-connected kgd topology with the point symbol {43}2{46}. In addition, the materials were thoroughly characterized using routine spectroscopic data and various analytical techniques. The catalytic activity of the microporous materials in the liquid-phase oxidation of styrene in acetonitrile, using 30% (wt) H2O2 as the oxidant, was investigated. The excellent performance of the monohydrous phase 3 was shown to be superior to the pristine framework and the anhydrous counterparts, as evidenced by a good turnover number (TON) and turnover frequency (TOF) = 82.6 and 21.0 h-1, respectively. Within 4 h, the substrates were catalytically oxidized to the desired products with up to 67% conversion and 100% benzaldehyde selectivity. It is worth noting that the accessible active metal sites and higher surface area enhanced the catalytic properties of 3. Furthermore, the maintenance of catalytic efficiency over five cycles and reusability are illustrated and discussed in terms of the structural differences of the microporous frameworks. Thus, a preliminary reaction mechanism for the selective oxidation of styrene is proposed. This study not only provides a fascinating example of MOF chromism achieved by thermal activation and rehydration but also sheds some light on the relationship between pore-surface- or metal-engineered sites in MOFs and their heterogeneous catalytic performances.

Pollution Characteristics，Sources，and Secondary Generation of Organic Acids in PM2.5 in Zhengzhou

Organic acids in atmospheric particulate matter are widely involved in various physical and chemical reactions in the atmosphere and contribute greatly to the formation of secondary organic aerosols and haze pollutions. Therefore， the concentration distribution characteristics， sources， and secondary formation of organic acids in particulate matter are of great significance for further investigation of organic aerosols and their secondary transformation. Fine particulate matter （PM2.5） samples were collected in Zhengzhou， and three types of organic acids， including dicarboxylic acids， fatty acids， and resin acids， were analyzed to explore their species distribution， seasonal variations， source contribution， and secondary generation. Malonic acid （di-C3） and succinate acid （di-C4） were the most abundant in the identified dicarboxylic acids， which showed obvious seasonal variations in the order of summer > autumn > winter > spring. Fatty acids had the highest concentration in winter and the lowest concentration in spring， showing obvious bimodal advantages， with the most abundant compounds being palmitic acid and stearic acid （C18）. Principal component analysis and multiple linear regression （MLR） were used to analyze the source of organic acids in PM2.5 in Zhengzhou； the results showed that 35% of the organic acids came from combustion and traffic sources， 24% from cooking sources， 23% from secondary formation， and 17% from natural sources. The ratios of the selected marker species （i.e.， di-C3 / di-C4， F/M， and C18：1 / C18） were used as tracers for the secondary formation of the organic aerosol and its aging process. The results showed that the photochemical reaction was intense in summer， and the proportion of organic aerosol aging or secondary production was high， whereas the photochemical reaction was weak in winter， and the aging degree of organic aerosol was low. Correlation analysis and MLR were used in combination to quantify the relative contribution of gas-phase oxidation and liquid-phase oxidation to dicarboxylic acid formation， and the results showed that gas-phase oxidation played a dominant role in the sampling period （accounting for 58%）， especially in summer （61%）.

Cobalt-nitrogen co-doped porous carbon sphere as highly efficient catalyst for liquid-phase cyclohexane oxidation with molecular oxygen and the active sites investigation

Cobalt-nitrogen co-doped porous carbon sphere as highly efficient catalyst for liquid-phase cyclohexane oxidation with molecular oxygen and the active sites investigation

Characterization of Organosulfates (OSs) in typical urban areas in Eastern China: Source, Process, and Volatility

Organosulfates (OSs) are an important component of secondary organic aerosols (SOA), accounting for ~30% of total organic aerosol. In this study, OSs in eastern China were investigated to understand their diurnal evolution, source, and volatility using high-resolution mass spectrometry. In polluted days, we identified a total of 5,147 organic molecules, including 1,206 OS molecules. The average molecular weight (m.w.) and carbon chain length of OSs in this study exceeded the commonly recognized range (500 Da). OSs were mostly composed of newly formed low oxidation state compounds as well as aged aliphatic and aromatic ones. The number and abundance of aromatic and aliphatic OSs with low saturation, volatility, O/Cw as well as H/Cw increased greatly with rising PM2.5 concentrations. The daytime photo-oxidation resulted in a large number of high m.w. (HMW, > 500 Da) OSs. OSs with m.w. <500 Da, and many oxygen atoms were newly generated during the nighttime, mainly dominated by liquid-phase oxidation processes. The result of OSs with higher m.w. and lower volatility was due to increased dimerization and oligomerization. During pollution formatting, OSs with small DBE values (between 0 and 6) appeared; meanwhile, the number of highly unsaturated OSs with DBE > 7 (mainly aromatic OSs) increased by about 34%. This study is useful for clarifying the secondary formation and properties of HMW OSs in a polluted environment in China.

Epoxidation of cyclohexene with cyclohexyl hydroperoxide

Objectives. To investigate the regularities of the process of joint production of epoxycyclohexane, cyclohexanol, and cyclohexanone using the cyclohexene epoxidation reaction with cyclohexyl hydroperoxide in the presence of an ammonium paramolybdate catalyst, representing an alternative to the method of cyclohexanol and cyclohexanone synthesis by alkaline catalytic decomposition of cyclohexyl hydroperoxide.Methods. The qualitative and quantitative analysis of the obtained intermediate and target compounds was determined using modern physicochemical research methods: gas–liquid chromatography using the Chromatec-Crystal 5000.2 hardware and software complex with a flame ionization detector and infrared spectroscopy on an RX-1 infrared Fourier spectrometer. The content of hydroperoxide in the oxidation products was determined using iodometric titration, while the carboxylic acid content was determined by the titrimetric method based on the neutralization reaction.Results. The presented method for obtaining cyclohexanol and cyclohexanone together with epoxycyclohexane by the reaction of cyclohexene epoxidation with cyclohexyl hydroperoxide containing cyclohexane in the products of high-temperature liquid-phase oxidation is experimentally substantiated. The influence of various technological parameters on the process of liquid-phase oxidation of cyclohexane to hydroperoxide is described. The conditions for carrying out this reaction are determined to ensure the achievement of a content of cyclohexyl hydroperoxide of 1.5 wt % in the products of oxidation. The regularities of the epoxidation reaction of the synthesized cyclohexyl hydroperoxide with cyclohexene in the presence of an ammonium paramolybdate catalyst are analyzed.Conclusions. Epoxidation of cyclohexene with cyclohexyl hydroperoxide produced epoxycyclohexane at a yield of 80–90% and a conversion of cyclohexane hydroperoxide of 85%.

On the effect of hafnium loading and location in mesoporous silica on the activity of catalysts in oxidation of dibenzothiophene

Oxidation of thiophenes to sulfones (easily extracted from fuel) is of crucial importance in petrochemical and automotive industry. The rational design and synthesis of stable catalysts of this process still remains one of the biggest challenges. In this work, a series of HfSBA-15 mesoporous materials with different hafnium content (3, 5 or 10 wt.%) has been prepared and studied in the liquid phase oxidation of dibenzothiophene (DBT) with H2O2. The activity of HfSBA-15 samples prepared by one-pot method was compared to that of Hf/SBA-15 synthesized by impregnation and that of HfMCF type of silica. It has been shown that hafnium loading and its location in the silica structure (framework and/or extra-framework positions) affect the efficiency of DBT oxidation. Moreover, the reaction conditions (i.e. oxidation temperature, reaction time, oxidant/sulfur ratio and catalyst amount) were optimized to achieve maximum conversion of dibenzothiophene (99 %). The location of hafnium species in SBA-15 and MCF materials was influenced by the loading of the metal and the type of silica structure (determined by the preparation method). Hafnium located in the framework of SBA-15 promoted generation of a higher number of active Lewis acid sites (LAS) and higher activity in oxidation of dibenzothiophene compared to extra-framework HfO2 species anchored in HfMCF material. It indicates that the location (framework vs extra-framework) and formation of isolated Hf4+ species are decisive for high activity of hafnium-doped mesoporous molecular sieves. This finding opens up a pathway for the development of highly efficient, stable and relatively cheap solid acid catalyst for oxidation of thiophenes to sulfones.

Photoactivation of Chlorine and Its Catalytic Role in the Formation of Sulfate Aerosols.

We present a novel mechanism for the formation of photocatalytic oxidants in deliquescent NaCl particles, which can greatly promote the multiphase photo-oxidation of SO2 to produce sulfate. The photoexcitation of the [Cl--H3O+-O2] complex leads to the generation of Cl and OH radicals, which is the key reason for enhancing aqueous-phase oxidation and accelerating SO2 oxidation. The mass normalization rate of sulfate production from the multiphase photoreaction of SO2 on NaCl droplets could be estimated to be 0.80 × 10-4 μg·h-1 at 72% RH and 1.33 × 10-4 μg·h-1 at 81% RH, which is equivalent to the known O3 liquid-phase oxidation mechanism. Our findings highlight the significance of multiphase photo-oxidation of SO2 on NaCl particles as a non-negligible source of sulfate in coastal areas. Furthermore, this study underscores the importance of Cl- photochemistry in the atmosphere.

Heterogeneous H2O2-based selective oxidations over zirconium tungstate α-ZrW2O8.

Catalytic properties of a crystalline zirconium tungstate, ZrW2O8, the material known mainly for its isotropic negative coefficient of thermal expansion, have been assessed for the liquid-phase selective oxidation of a range of organic substrates comprising CC, OH, S and other functional groups using aqueous hydrogen peroxide as the green oxidant. Samples of ZrW2O8 were prepared by hydrothermal synthesis and characterised by N2 adsorption, PXRD, SEM, EDX, FTIR and Raman spectroscopic techniques. Studies by IR spectroscopy of adsorbed probe molecules (CO and CDCl3) revealed the presence of Brønsted acidic and basic sites on the surface of ZrW2O8. It was demonstrated that ZrW2O8 is able to activate H2O2 under mild conditions and accomplish the epoxidation of CC bonds in alkenes and unsaturated ketones, oxidation of thioethers to sulfoxides and sulfones, along with the oxidation of alcoholic functions to produce ketones and aldehydes. The oxidation of tetramethylethylene and α-terpinene over ZrW2O8 revealed the formation of peroxidation products, 2,3-dimethyl-3-butene-2-hydroperoxide and endoperoxide ascaridole, respectively, indicating the involvement of singlet oxygen in the oxidation process. The ZrW2O8 catalyst preserves its structure and morphology under the turnover conditions and does not suffer from metal leaching. It can be easily recovered, regenerated by calcination, and reused without the loss of activity and selectivity.

Exploring the oxidation chemistry of diethyl carbonate in lithium-ion battery thermal runaway using SVUV-PIMS

With the extensive applications of lithium-ion batteries and widespread concerns about their security, it is necessary to deeply understand the reaction mechanism of thermal runaway process of Li-ion batteries. Oxygen released from cathode and anode materials could react with electrolyte solvents with increased temperatures. However, the chemical mechanism remains elusive due to the complexity of the battery system. In this work, we developed a method to study the oxidation chemistry of electrolyte solvents and oxygen in lithium-ion battery thermal runaway process. The liquid phase oxidation of diethyl carbonate (DEC) with oxygen was studied in a closed autoclave with diverse oxygen concentrations, temperatures and reaction times. The samples were measured by synchrotron vacuum ultraviolet radiation photoionization mass spectrometry (SVUV-PIMS) to quantitatively analyze the oxidation products. It was found that the onset reaction temperature is less than 120 °C, which indicates that it maybe occurs in the early stage of Li-ion battery thermal runaway. Besides, the feasible reaction scheme is discussed to rationalize the formation of the primary products.

Synthesis of diethylene glycol ester of synthetic fatty acids, obtained from liquid phase oxidation of paraffin hydrocarbons C11 and C14

Synthesis of diethylene glycol ester of synthetic fatty acids, obtained from liquid phase oxidation of paraffin hydrocarbons C11 and C14

Catalysts Based on Iron Oxides for Wastewater Purification from Phenolic Compounds: Synthesis, Physicochemical Analysis, Determination of Catalytic Activity

In this work, the synthesis of magnetite nanoparticles and catalysts based on it stabilized with silicon and aluminum oxides was carried out. It is revealed that the stabilization of the magnetite surface by using aluminum and silicon oxides leads to a decrease in the size of magnetite nanocrystals in nanocomposites (particle diameter less than ~10 nm). The catalytic activity of the obtained catalysts was evaluated during the oxidation reaction of phenol, pyrocatechin and cresol with oxygen. It is well known that phenolic compounds are among the most dangerous water pollutants. The effect of phenol concentration and the effect of temperature (303–333 K) on the rate of oxidation of phenol to Fe3O4/SiO2 has been studied. It has been determined that the dependence of the oxidation rate of phenol on the initial concentration of phenol in solution is described by a first-order equation. At temperatures of 303–313 K, incomplete absorption of the calculated amount of oxygen is observed, and the analysis data indicate the non-selective oxidation of phenol. Intermediate products, such as catechin, hydroquinone, formic acid, oxidation products, were found. The results of UV and IR spectroscopy showed that catalysts based on magnetite Fe3O4 are effective in the oxidation of phenol with oxygen. In the UV spectrum of the product in the wavelength range 190–1100 nm, there is an absorption band at a wavelength of 240–245 nm and a weak band at 430 nm, which is characteristic of benzoquinone. In the IR spectrum of the product, absorption bands were detected in the region of 1644 cm−1, which is characteristic of the oscillations of the C=O bonds of the carbonyl group of benzoquinone. The peaks also found at 1353 cm−1 and 1229 cm−1 may be due to vibrations of the C-H and C-C bonds of the quinone ring. It was found that among the synthesized catalysts, the Fe3O4/SiO2 catalyst demonstrated the greatest activity in the reaction of liquid-phase oxidation of phenol.

Catalytic properties of nanostructured graphene in liquid-phase oxidation of naphthene-paraffin hydrocarbons of petroleum mineral oils

Catalytic properties of nanostructured graphene in liquid-phase oxidation of naphthene-paraffin hydrocarbons of petroleum mineral oils

Intercalation of pyrazolone-based oxalamide metal complexes into Na-montmorillonite for catalytic liquid-phase oxidation of phenol using H2O2.

The intercalation of pyrazolone-based oxalamide metal complexes into Na-montmorillonite (Na-MMT) for catalytic liquid-phase oxidation of phenol using H2O2 was undertaken by a flexible ligand method using metal ions including Mn(II), Zn(II), and Sn(II). First, the metal ions were exchanged with the sodium ions of Na-MMT, and then these metal ions were complexed with a new pyrazolone-based oxalamide ligand. The intercalated metal complexes were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, elemental analysis, and thermogravimetric analysis. Phenol was successfully oxidized by heterogeneous catalysts based on Mn(II), Zn(II), and Sn(II) pyrazolone-based oxalamide complexes intercalated into Na-MMT. These heterogeneous catalysts catalyze the liquid-phase oxidation of phenol using H2O2 to catechol as the major product and hydroquinone and benzoquinone as the minor products. The Mn(II) and Zn(II) complexes intercalated into Na-MMT showed better activity than the Sn(II) complex intercalated into Na-MMT and the reaction without the catalyst. It has been shown that some metal ion complexes intercalated into Na-MMT are active catalysts for liquid-phase oxidation of phenol with hydrogen peroxide.