Liquid-phase Oxidation Research Articles

Enhanced mechanical property of continuous carbon fiber/polyamide thermoplastic composites by combinational treatments of carbon fiber fabric

To fabricate continuous carbon fiber (CF)/polyamide (PA 6) thermoplastic composites with high strength and stiffness, combinational treatments of liquid phase oxidation, coupling agent, and coating were adopted to improve the surface activity of CF fabric and interfacial bonding with PA 6 matrix. The mechanical properties, dynamic thermomechanical properties, microstructure, and hydrothermal aging behavior of the CF/PA 6 composites were studied. The XPS results showed the N, O, and Si elements as well as the C–O, CO, and C–Si groups were significantly increased on the CF surface, indicating the improvement of chemical activity and KH550 effectively grafted. The tensile strength significantly increased from 396 MPa to 480 MPa, by 21.2%, and Young's modulus increased from 38.6 GPa to 47.9 GPa, by 24.1%, respectively. The result of the damp heat aging test in 240 h showed the retention rate of flexural strength and ILSS were 66% and 67%, respectively.

Cu2O@TiO2 core-shell microspheres for naphthalene oxidation

New Cu2O@TiO2 core-shell microspheres were successfully prepared for the first time in this paper. The XRD, N2 adsorption-desorption, SEM, TEM, EDX and XPS characterizations were utilized to investigate the physical and chemical properties. The liquid phase oxidation of naphthalene was also carried out to test their catalytic performance. The characterization results indicating that the Cu2O microspheres were firstly formed by hydrothermal treatment and the rutile TiO2 coating on the surface would be formed by the hydrolysis of tetrabutyl titanate. The Cu2O@TiO2-5.0 catalyst with the molar ratio of copper to titanium species as high as 5.0 has the largest surface area and maximum pore volume resulting from the integrated microspheres with rougher surface thickness of about 6.3 nm, and it showed higher catalytic performance in the liquid phase oxidation of naphthalene. Naphthalene conversion of 43.2%, 1, 4-naphthoquinone selectivity of 26.7% and phthalic anhydride selectivity of 53.4% can be obtained, and it only slightly decreased even after repeated use for 5 times. The method would provide a valuable theoretic reference for the hindrance of Cu2O rapid deactivation and the industrial application of the naphthalene oxidation to produce high valuable chemicals.

5,8-Di-tert-butyl-2-hydroxy-1H-benzo[de]isoquinoline-1,3(2H)-dione—A New Lipophilic N-oxyl Radical Precursor

N-hydroxyimides are widely known as organocatalysts for aerobic oxidation and oxidative coupling reactions, in which corresponding imide-N-oxyl radicals play the role of catalytically active hydrogen atom abstracting species. The drawbacks of many N-hydroxyimides are poor solubility in low polarity solvents and limited activity in the cleavage of unactivated C–H bonds. To overcome these shortcomings, we have synthesized a new lipophilic N-hydroxyimide, 5,8-di-tert-butyl-2-hydroxy-1H-benzo[de]isoquinoline-1,3(2H)-dione, with high solubility in low-polarity solvents such as DCM. According to the EPR study, the stability of the corresponding imide-N-oxyl radical is comparable to that of the non-tert-butylated analogue, naphthalimide-N-oxyl radical. DFT calculations showed that the NO–H bond dissociation enthalpy (BDE) in the synthesized tert-butylated-N-hydroxynaphthalimide is one of the highest in N-hydroxyimide series, which corresponds to high hydrogen atom abstracting reactivity and may be useful in catalysis of strong C–H bond oxidative cleavage. The synthesized compound can be considered as catalyst for liquid-phase free-radical oxidation and oxidative coupling reactions in non-polar media where solubility was previously the limiting factor.

Near Infrared Light-to-Heat Conversion for Liquid-Phase Oxidation Reactions by Antimony-Doped Tin Oxide Nanocrystals.

Effective utilization of the sunlight for chemical reactions is pivotal for dealing with the growing energy and environmental issues. So far, much effort has been focused on the development of semiconductor photocatalysts responsive to UV and visible light. However, the near infrared and infrared (NIR-IR) light occupying ∼50 % of the solar energy has usually been wasted because of the low photon energy insufficient for the band gap excitation. Antimony doping into SnO2 (ATO) induces strong absorption due to the conduction band electrons in the NIR region. The absorbed light energy is eventually converted to heat via the interaction between hot electrons and phonons. This Concept highlights the photothermal effect of ATO nanocrystals (NCs) on liquid-phase oxidation reactions through the NIR light-to-heat conversion. Under NIR illumination even at an intensity of ∼0.5 sun, the reaction field temperature on the catalyst surface is raised 20-30 K above the bulk solution temperature, while the latter is maintained near the ambient temperature. In some reactions, this photothermal local heating engenders the enhancement of not only the catalytic activity and selectivity but also the regeneration of catalytically active sites. Further, the photocatalytic activity of semiconductors can be promoted. Finally, the conclusions and possible subjects in the future are summarized.

Synthesis and kinetic analysis of green AA-type monomers using linoleic acid through bromide promoted transition metal-catalyzed oxidation with air

The present study explores the renewable route to synthesize AA-type monomers for condensation polymerization, namely adipic and azelaic acid, from linoleic acid (LA) using a bromide-promoted transition metal catalyst. For this, liquid-phase catalytic oxidation of LA is carried out using a catalyst system involving the acetates of Cobalt(II) and Manganese(II) and hydrogen bromide in an acetic acid green solvent at temperature: 393–423 K and a pressure of 5.8–8.8 bar in the air. The oxidation products are confirmed by a gas chromatography-mass spectrometer and carbon dioxide analyzer. At the early stage of LA oxidation (i.e.,<5.0 h), the identified major products are malonic acid, azelaic acid, and adipic acid, whereas malonic acid decomposes to carbon dioxide after increasing oxidation time. The influence of process variables, i.e., (i) the loading of LA, bromide, Cobalt(II), and Manganese(II), (ii) temperature, and (iii) pressure on LA conversion and yield of adipic acid and azelaic acid have also been carried out, and the loading of catalyst, pressure, and temperature plays a vital role on the LA conversion and product yields. The temperature-dependent kinetic parameters are also determined, and the rate-controlling step for LA oxidation is analyzed and further extended by evaluating the Hatta number and enhancement factor. The lower values of the Hatta numbers and enhancement factors suggest that the oxidation using air is controlled by the diffusion of oxygen and reaction in the film, and adequate gas-liquid mixing will improve the rate of LA oxidation.

Liquid-phase oxidation synthesis of WS2 –WO3 particles with enhanced gas sensing performance

In this study, [Formula: see text] particles were successfully synthesized by a solvothermal liquid-phase oxidation process under various conditions and their gas sensing performance was evaluated at room temperature. The sample synthesized in ethanol-rich solvent at 210[Formula: see text]C showed excellent gas sensing performance. It is suggested that the crystalline phase and the particle morphology, which are essential for improving gas sensing performance, are effectively controllable by the present liquid phase oxidation process.

Influence of stabilisers on the catalytic activity of supported Au colloidal nanoparticles for the liquid phase oxidation of glucose to glucaric acid: understanding the catalyst performance from NMR relaxation and computational studies

Impact of stabilisers on the catalytic performance of supported Au colloidal nanoparticles for the liquid phase oxidation of glucose to glucaric acid.

A-site defective La2-xCuO4 perovskite-type oxides for efficient oxidation of cyclohexylbenzene.

Phenol production through the oxidation of cyclohexylbenzene (CHB) and the subsequent decomposition of tertiary hydroperoxide has attracted more and more attention. In this study, defective La2-xCuO4 perovskite-type oxide catalysts with tunable A-site deficient structures and abundant surface oxygen vacancies were developed for the liquid phase oxidation of CHB to produce cyclohexylbenzene-1-hydroperoxide (CHBHP). By tuning the amount of A-site La ions in the perovskite structure, more surface oxygen vacancies and Cu+ species were formed in catalysts. The A-site-deficient La1.9CuO4 catalyst achieved significant catalytic efficiency along with a high CHBHP yield of 27.6% at 48.6% CHB conversion under reaction conditions (i.e., 120 °C and 12 h), outperforming those of other transition metal-based catalysts previously reported in the literature. A series of structural characterization methods and catalytic reactions highlighted the crucial roles of surface oxygen vacancies and metal La and Cu ions in the oxidation process. It was revealed that metal ions favored CHB adsorption and activation, while surface oxygen vacancies facilitated the creation of active adsorbed oxygen species. The present study offers an opportunity for the future design of new high-efficiency heterogeneous catalyst systems for CHB oxidation to obtain phenol.

Zeolite encapsulated organometallic complexes as model catalysts.

Heterogeneities in the structure of active centers in metal-containing porous materials are unavoidable and complicate the description of chemical events occurring along reaction coordinates at the atomic level. Metal containing zeolites include sites of varied local coordination and secondary confining environments, requiring careful titration protocols to quantify the predominant active sites. Hybrid organometallic-zeolite catalysts are useful well-defined platform materials for spectroscopic, kinetic, and computational studies of heterogeneous catalysis that avoid the complications of conventional metal-containing porous materials. Such materials have been synthesized and studied previously, but catalytic applications were mostly limited to liquid-phase oxidation and electrochemical reactions. The hydrothermal stability, time-on-stream stability, and utility of these materials in gas-phase oxidation reactions are under-studied. The potential applications for single-site heterogeneous catalysts in fundamental research are abundant and motivate future synthetic, spectroscopic, kinetic, and computational studies.

Исследование теплофизических процессов получения различных алюмоматричных композитов

The possibilities of obtaining aluminum matrix composite materials of the composition Al−Al2O3 are considered by the method of liquid-phase oxidation of aluminum by purging the melt with oxygen. The obtained materials are a two-phase system with different concentrations of the solid phase. An algorithm for calculating the kinetics of aluminum oxidation in obtaining the oxide phase of an aluminum matrix composite is proposed. It is established that the beginning and completeness of the reaction on the surface of the gas bubble determines the synthesis of the oxide phase and is determined by the functions T(t), h(t) in the region of dynamic time delay, which, in turn, the queue is revealed as a function of the temperature in the contact zone of the gas bubble with the melt, taking into account the duration of the heating of the bubble along the cross section and the radius of the bubble itself. The microstructures of the obtained materials with different structural-phase state with variations in the time of purging and oxygen supply to the aluminum melt are presented

Investigation of thermophysical processes of obtaining various aluminum matrix composites

The possibilities of obtaining aluminum matrix composite materials of the composition Al-Al2O3 are considered by the method of liquid-phase oxidation of aluminum by purging the melt with oxygen. The obtained materials are a two-phase system with different concentrations of the solid phase. An algorithm for calculating the kinetics of aluminum oxidation in obtaining the oxide phase of an aluminum matrix composite is proposed. It is established that the beginning and completeness of the reaction on the surface of the gas bubble determines the synthesis of the oxide phase and is determined by the functions T(t), h(t) in the region of dynamic time delay, which, in turn, the queue is revealed as a function of the temperature in the contact zone of the gas bubble with the melt, taking into account the duration of the heating of the bubble along the cross section and the radius of the bubble itself. The microstructures of the obtained materials with different structural-phase state with variations in the time of purging and oxygen supply to the aluminum melt are presented. Keywords: aluminum matrix composite material, high temperature oxidation, gas bubble.

Механизм реакции жидкофазного аэробного окисления углеводородов в присутствии металлсодержащих катализаторов

The review presents the mechanisms of the process of liquid-phase oxidation of hydrocarbons in the presence of catalysts of various structures. It has been determined that this area requires further study of the mechanism of hydrocarbon destruction processes, which is influenced by many reaction parameters.

An efficient and universal solar interfacial photothermal reactor toward liquid phase oxidation

AbstractPhotothermal catalysis has attracted great attention owing to high solar energy utilization efficiency, and great progress has been achieved in gas‐phase catalysis. However, photothermal catalysis in liquid‐phase shows a limited performance, due to high specific heat capacity of liquid. Herein, an interfacial photothermal catalytic (IPC) strategy applying an IPC leaf was designed for liquid‐phase catalysis using benzyl alcohol oxidation as the model reaction. On even ground, the benzaldehyde generation rate (8.7 mmol gcat−1 h−1) of the IPC system with Ce‐doped MnO2 as photothermal catalyst was almost 4.8 times and 3 times of bulk photothermal catalysis and the relative bulk thermal catalysis. Experimental results proved that this excellent catalytic performance could be attributed to both the high temperature achieved and the enhanced lattice oxygen activity by solar irradiation. This IPC system also exhibited good universality and long‐term durability. Our work innovatively created a green strategy to obtain fine chemicals with only solar irradiation.

Easy and Versatile Synthesis of Bulk Quantities of Highly Enriched 13C-Graphene Materials for Biological and Safety Applications.

The preparation of bulk quantities of 13C-labeled graphene materials is relevant for basic investigations and for practical applications. In addition, 13C-labeled graphene materials can be very useful in biological and environmental studies, as they may allow the detection of graphene or its derivatives in cells or organs. In this paper, we describe the synthesis of 13C-labeled graphene materials (few-layer graphene, FLG, and graphene oxide, GO) on a tens of mg scale, starting from 13C-labeled methane to afford carbon fibers, followed by liquid-phase exfoliation (FLG) or oxidation (GO). The materials have been characterized by several analytical and microscopic techniques, including Raman and nuclear magnetic resonance spectroscopies, thermogravimetric analysis, X-ray photoelectron spectroscopy, and X-ray powder diffraction. As a proof of concept, the distribution of the title compounds in cells has been investigated. In fact, the analysis of the 13C/12C ratio with isotope ratio mass spectrometry (IRMS) allows the detection and quantification of very small amounts of material in cells or biological compartments with high selectivity, even when the material has been degraded. During the treatment of 13C-labeled FLG with HepG2 cells, 4.1% of the applied dose was found in the mitochondrial fraction, while 4.9% ended up in the nuclear fraction. The rest of the dose did not enter into the cell and remained in the plasma membrane or in the culture media.

CeO2–TiO2 Nanoparticle-Grafted gC3N4 Sheets as an Efficient Catalyst for the Oxidation of Cyclohexane to KA oil

Here, we report a sustainable catalytic process operating on CeO2–TiO2 nanoparticle-grafted gC3N4 sheets (gC3N4/CeO2–TiO2) in the presence of a H2O2 green oxidant for the liquid phase oxidation of cyclohexane to produce KA oil (cyclohexanone + cyclohexanol). The process achieved enhanced cyclohexane conversion (62%) toward 95% KA oil (cyclohexanone 83% + cyclohexanol 12%), which is the highest ever reported to the best of our knowledge. The excellent catalytic behavior of gC3N4/CeO2–TiO2 in the present study due to its enhanced active sites, that is, Ce3+ and Ti3+, is facilitated by the redox reaction between CeO2–TiO2 and gC3N4 sheets. The high stability of gC3N4/CeO2–TiO2 catalyst in the liquid phase reaction study indicates the robust nature of this catalyst facilitated by strong interactions between CeO2–TiO2 species and electron-rich sites (N and π) of gC3N4 sheets. The overall study suggests that the gC3N4/CeO2–TiO2 material can be a promising catalyst for the sustainable production of KA oil from cyclohexane oxidation in the presence of the H2O2 oxidant.

Kinetic Modeling of Homogenous Catalytic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

2,5-Furandicarboxylic acid (FDCA) is a valuable biomass-based monomer with broad market prospects that can replace terephthalic acid (TPA) in all kinds of polymer applications. In this work, the homogeneous catalytic oxidation of 5-hydroxymethylfurfural (HMF) to FDCA was investigated over a Co/Mn/Br catalyst with acetic acid/water as a solvent. On the basis of free radical oxidation reaction mechanisms, one simplified main reaction kinetic model for the oxidation of HMF with six parameters was proposed, which considered the formation of FDCA and the most important intermediates. The effects of catalyst, temperature, and water content on the liquid-phase oxidation kinetics of HMF were investigated. The model fitted the experimental data well, in which only the chain initiation rate constant was found to be dependent on experimental conditions, while other rate constants can be kept constant in the investigated range. Hopefully, the kinetic model in this work can provide valuable insights for the design and optimization of the industrial process of HMF oxidation to FDCA.

Investigation of the Adsorption Properties of a Nanodiamond Surface after Liquid-Phase Oxidation

Investigation of the Adsorption Properties of a Nanodiamond Surface after Liquid-Phase Oxidation

Enhanced Catalytic Performance of a Ce/V Oxo Cluster through Confinement in Mesoporous SBA-15.

To increase catalytic efficiency, mesoporous supports have been widely applied to immobilize well-defined metal oxide clusters due to their ability to stabilize highly dispersed clusters. Herein, a redox-active heterometallic Ce12V6-oxo cluster (CeV) was first presynthesized and then incorporated into mesoporous silica, SBA-15, via a straightforward impregnation method. Scanning transmission electron microscopy (STEM) and Fourier transform infrared spectroscopy (FTIR), in concert with scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS), verified the successful introduction of the CeV cluster inside the pore of SBA-15. The 51V magic angle spinning solid-state nuclear magnetic resonance (51V MAS NMR) spectroscopy and differential pair distribution function (dPDF) analysis confirmed the structural integrity of the CeV cluster inside the SBA-15. The composite was then benchmarked for liquid-phase oxidation of 2-chloroethyl ethyl sulfide (CEES) under mild conditions and gas-phase oxidative dehydrogenation (ODH) of propane under high temperatures (up to 550 °C). The catalytic reactivity results demonstrated 8- and 14-fold increase in turnover frequency (TOF) values of the composite (CeV@10SBA-2) than the bulk CeV cluster under the same conditions for CEES oxidation and ODH, respectively. These results highlight the improved reactivity of the catalytically active CeV cluster as attributed to the higher dispersion of the discrete cluster upon immobilization within the SBA-15 support.

Mechanistic Impacts of Metal Site and Solvent Identities for Alkene Oxidation over Carboxylate Fe and Cr Metal–Organic Frameworks

Isolated Fe(III) and Cr(III) sites contained in nanoporous voids of isoreticular carboxylate MIL-101(Fe) and MIL-101(Cr) are interrogated for their reactivity and selectivity of liquid-phase styrene oxidation by hydrogen peroxide (H2O2). Batch kinetic measurements in acetonitrile (MeCN) at 323 K showcase that both metal-normalized oxygenate production and H2O2 consumption rates are O(101) higher for MIL-101(Fe) than MIL-101(Cr). Thermodynamically consistent reaction pathways, constructed through spiking experiments, reveal complex interconnectivities between primary (styrene oxide, benzaldehyde) and secondary (styrene glycol, benzoic acid, phenylacetaldehyde) oxygenates. Though benzaldehyde is the majority product for both MIL-101(Fe) and MIL-101(Cr), isoconversion (Xstyrene = 7%) product distributions suggest intrinsic differences in preferred reaction pathways. Apparent energy barriers for all pathways are lower over MIL-101(Fe) than for MIL-101(Cr), conferred by metal electron affinity differences for primary oxygenate selectivity, while secondary (inter)conversion rates trend with acid site densities. Fitted rate laws, radical trapping, adsorption experiments, and complementary DFT calculations indicate surface-mediated reactions by H2O2-derived surface species that outcompete bound styrene, product oxygenate, solvent, and water molecules for both MIL-101(Fe) and MIL-101(Cr) in MeCN. Extracted enthalpic and entropic effects from temperature-dependent experiments (318–328 K) in MeCN and MeOH showcase the ability of hydrogen bonding solvents in locally hydrophilic environments to selectively stabilize primary oxygenate transition states and indicate additional confinement effects from microporous substructures in MIL-101(Fe) and MIL-101(Cr). Simplified rate expressions are expanded to encompass first-order catalyst deactivation rates through temporal metal leaching experiments and assert that metal leaching dominates MIL-101(Cr) catalyst inefficiencies, while a combination of metal leaching and other (ir)reversible site changes are present for MIL-101(Fe). Overall, this work combines kinetic, spectroscopic, numerical, and computational approaches to rigorously define reaction and deactivation mechanisms for styrene oxidation by H2O2 over isoreticular MIL-101(Fe) and MIL-101(Cr).

Catalytic properties of Ce-MCM-41 prepared with ceric ammonium nitrate in the liquid-phase oxidation of benzyl alcohol

This work reports the influence of microstructural features in the catalytic performance, reaction kinetics and stability of a cerium-modified MCM-41 material prepared with ceric ammonium nitrate (Ce-MCM-CAN) in the liquid-phase oxidation of benzyl alcohol with tert-butyl hydroperoxide (TBHP) as oxidant. All the mentioned features were compiled and compared to other two Ce-MCM-41 catalysts prepared with CeCl3·7H2O and Ce(NO3)3·6H2O (Ce-MCM-Cl and Ce-MCM-NO3, respectively). Ce-MCM-CAN sample has offered a unique catalytic profile and considerable resistance towards conversion of isomorphous cerium sites in inactive agglomerated CeO2. In a typical catalytic essay at 80 °C and 24 h, Ce-MCM-CAN sample attains 54.6% of conversion, with 47.4 and 25.9% of benzaldehyde selectivity and yield, respectively. Nonetheless, kinetic essays demonstrates that the reaction continues after 24 h, mainly by reducing the aldehyde's selectivity and favoring the formation of benzoic acid, whereas Ce-MCM-Cl and Ce-MCM-NO3 samples has product formation stagnated after 20 h. After four catalytic cycles, the deactivation of Ce-MCM-CAN sample occurs mainly after the first cycle (reduction of 19.8% in conversion) with little influence in TBHP efficiency, while the other two model catalysts deactivate progressively after each cycle (reduction of 33.3 and 23.6% in conversion for Ce-MCM-Cl and Ce-MCM-NO3 samples, respectively) with loss of oxidant usage. Overall, the long-range ordering and pre-existing non-framework CeO2 nanoparticles in Ce-MCM-CAN sample is responsible for decreasing the deactivation rate. Such properties emerge from the counterbalanced synergy between chaotropic nitrate anions and condensation between [Ce(OH)4] species with silicate anions.