Catalytic Oxidation System Research Articles

Study of Neat and Mixed Sn(IV) and Mo(VI) Oxides for Transesterification and Esterification: Influence of the Substrate on Leaching

Tin and molybdenum oxide catalytic systems were employed in transesterification and esterification reactions using methanol. In the presence of the molybdenum-based catalysts, low activity was observed in the methanolysis of soybean oil. However, high activity was attained in the case of ethyl acetate transesterification (conversion of 75% at 1 h, using SnMo50 as catalyst) and oleic or propionic acid esterification (conversion of 48% at 1 h, in the case of propionic acid, using SnMo50 as catalyst). This result may be associated with the formation of molybdenum carboxylates that are soluble in more polar media and are responsible for the catalytic activity. These results suggest that the conversions observed with these systems can be related to the formation of homogeneous catalytic complexes, promoting better diffusion of the substrate and the acid sites of these systems.

Catalytic reaction system for rapid selective oxidation of alkyl sulphide

Highly efficient catalytic reaction systems are developed to rapidly and selectively oxidize 2-chloroethyl ethyl sulfide (CEES). In the systems, precursors containing bromide(s) and nitrate anions are chosen for the development of cyclic catalytic loop and the effect of acids on the selective oxidation of CEES are investigated by the addition of several homogeneous acid catalysts. The experimental results reveal that addition of acid results in a higher concentration of tribromide, which is reported as a key component for the observed activity in the catalytic solution. As a consequence, a dramatic improvement in catalytic activity is observed, especially when the molar amount of acid is controlled to be more than twice the initial concentration of tribromide. For the efficient design of a catalytic system, heterogeneous acid catalysts possessing different ratios of Brønsted to Lewis acid sites are also considered. Compared to reaction systems catalysed by homogeneous acids, similar reaction behaviour is observed for the reaction with Amerlyst-15, while those with other heterogeneous catalysts, containing Lewis or mixed acid sites in their structure, exhibits an adverse effect of selective sulfoxidation, mainly due to the adsorption of anions onto Lewis sites and consequential deconstruction of the catalytic loop.

Selective aerobic oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran catalyzed by Cu-based metal organic frameworks with 2,2,6,6-tetramethylpiperidin-oxyl

Abstract While Cu combined with 2,2,6,6-tetramethylpiperidin-oxyl (TEMPO) constitutes a novel oxidative catalytic system using O2 for oxidation of 5-hydroxymethylfurfural (HMF), few studies have been conducted to investigate Cu/TEMPO/O2 for oxidation of HMF to 2,5-diformylfuran (DFF). More importantly, existing studies employ homogeneous Cu species, which is difficult for recovery; thus it is crucial to develop heterogeneous Cu catalyst incorporated with TEMPO for oxidation of HMF. Herein, a Cu-based metal organic frameworks (MOFs), HKUST-1, is proposed and employed for the first time as a heterogeneous catalyst with TEMPO for oxidative conversion of HMF to DFF in the presence of O2. Although TEMPO and HKUST-1 are ineffective separately for oxidation of HMF to DFF, the combination of HKUST-1 and TEMPO successfully converts HMF to DFF without by-products. The reaction duration could be as short as 3 h at 120 °C to achieve > 96% of HMF conversion with a selectivity > 99% and a yield of 96%, demonstrating that this HKUST-1+TEMPO+O2 is certainly promising and highly selective for HMF conversion to DFF. HKUST-1 is also reusable for incorporating with TEMPO to oxidize HMF to DFF. These results indicate that HKUST-1 is an advantageous heterogeneous catalyst for HMF conversion using TEMPO as an oxidant catalyst.

Aerobic oxidative aromatization of Hantzsch 1,4-dihydropyridines via an anomeric-based oxidation in the presence of Laccase enzyme/4-Phenyl urazole as a cooperative catalytic oxidation system

Cooperative catalytic system of Laccase enzyme (from Trametes versicolor) and 4-phenyl urazole in phosphate buffer/acetonitrile solution at 40 °C has been applied for the biomimetic aerobic oxidative aromatization of Hantzsch 1,4-dihydropyridines (1,4-DHPs) with excellent yields.

One-Pot Synthesis of Photoluminescent Self-Assembled Carbon Dot Monolayer Films

We propose a facile and simple synthesis of photoluminescent (PL) carbon dot self-assembled monolayer films (CD-SAMFs) at oil-water interfaces. By using styrene both as the carbon source and the oil phase medium, we got our amazing CD-SAMFs under the copper acetate and hydrogen peroxide (Cu(Ac)2-H2O2) catalytic-oxidation system. Without any surface modification, the spontaneously formed CD-SAMFs exhibit ultrathin thickness (<10 nm), bright luminescence, high transparency, and hydrophobicity, which have the potential as a new alternative to be used on multifunctional coating films, anticounterfeiting, displays, sensors, and optical devices.

Synthesis and characterization of TBA-PV2Mo10@PVA as an efficient and reusable heterogeneous catalyst for oxidative desulfurization of gasoline

To prepare ultra-clean gasoline fuel, a new nanocomposite TBA-PV2Mo10@PVA was introduced as an efficient and green catalyst for oxidative desulfurization (ODS) process. The nanocomposite was successfully prepared by reaction of tetrabutylammonium bromide (TBA), H5PMo10V2O40, and poly vinyl alcohol (PVA) at room temperature via sol–gel method under oil-bath condition. The synthesized TBA-PV2Mo10@PVA was characterized by FT-IR, XRD, UV-vis, SEM and 31P NMR spectroscopy. The catalytic activity of catalyst was tested on the ODS of gasoline in the presence of CH3COOH/H2O2 (1/1 volume ratio) as oxidant system and results were compared with model sulfur compounds (MSCs). After 2 h, the results were shown that the removal of total sulfur content could be reduced to 97% at the temperature of 35 °C. The main factors affecting the desulfurization efficiency, including catalyst dosage and temperature were investigated in detail. In addition, the kinetic parameters of oxidation of MSCs, reaction mechanism, and reusability of catalyst were discussed. The TBA-PV2Mo10@PVA nanocatalyst was separated and reused conveniently at the end of the reaction for five times. The excellent performance of this catalytic oxidation system can be a promising rout to achieve ultra-clean gasoline.

Steady state isotopic transient kinetic analysis of the combustion of CH4 over Co-Mn-O catalysts

The main objective of the research was the analysis of the number and intrinsic activity of active sites present on the surface of working cobalt-manganese-based catalytic systems for complete methane oxidation. The obtained values of these parameters strongly depend on the reaction temperature and chemical composition of studied catalysts. The highest number of active sites is present on the surface of the cobalt-manganese catalyst, which demonstrates the best catalytic activity in methane oxidation. Nevertheless, in some temperature ranges intrinsic activity of its active sites is lower than that of the active sites present on the surface of other catalysts.

A Study of Catalytic Oxidation of a Library of C₂ to C₄ Alcohols in the Presence of Nanogold.

The classical stoichiometric oxidation of alcohols is an important tool in contemporary organic chemistry. However, it still requires huge modifications in order to comply with the principles of green chemistry. The use of toxic chemicals, hazardous organic solvents, and the large amounts of toxic wastes that result from the reactions are a few examples of the problems that must be solved. Nanogold alone or conjugated with palladium were supported on different carriers (SiO2, C) and investigated in order to evaluate their catalytic potential for environmentally friendly alcohol oxidation under solvent-free and base-free conditions in the presence H2O2 as a clean oxidant. We tested different levels of Au loading (0.1–1.2% wt.) and different active catalytic site forms (monometallic Au or bimetallic Au–Pd sites). This provided new insights on how the structure of the Au-dispersions affected their catalytic performance. Importantly, the examination of the catalytic performance of the resulting catalysts was oriented toward a broad scope of alcohols, including those that are the most resistant to oxidation—the primary aliphatic alcohols. Surprisingly, the studies proved that Au/SiO2 at a level of Au loading as low as 0.1% wt. appeared to be efficient and prospective catalytic system for the green oxidation of alcohol. Most importantly, the results revealed that 0.1% Au/SiO2 might be the catalyst of choice with a wide scope of utility in the green oxidation of various structurally different alcohols as well as the non-activated aliphatic ones.

Catalytic Wacker‐type Oxidations Using Visible Light Photoredox Catalysis

AbstractA combined palladium/photoredox catalytic system for the efficient oxidation of terminal olefins to the corresponding methyl ketones is presented. The interplay of air, water, and light leads to a protocol in which the stoichiometric oxidants required for oxidative palladium catalysis are substituted with catalytic, single‐electron transfer processes. Detailed mechanistic investigations revealed the role of the key components, in situ generated species, and catalysts. A broad range of substrates was examined in homogeneous as well as heterogeneous photoredox protocols, delivering the desired products in good yields.

Iron-Decorated, Guanidine Functionalized Metal-Organic Framework as a Non-heme Iron-Based Enzyme Mimic System for Catalytic Oxidation of Organic Substrates

A novel porous functionalized metal-organic framework (MOF) as a non-heme iron-based enzyme mimic system was achieved via two-step post-synthetic modification of the MIL-101(Cr)-NH2, and characterized by FT-IR, PXRD, TGA, SEM, EDS, CHN, BET surface area, and ICP-OES analyses. This new modified MOF (MIL-101(Cr)-guanidine-Fe) has been demonstrated to be a highly efficient, active, and reusable catalyst for oxidation of various organic substrates, including alcohols, alkenes and alkyl arenes at room temperature using H2O2 as an oxidant.

Green Synthesis of 2‐Substituted Imidazolines using Hydrogen Peroxide Catalyzed by Tungstophosphoric Acid and Tetrabutylammonium Bromide in Water

Various 2‐substituted imidazolines were constructed from aromatic aldehydes with ethylenediamine using hydrogen peroxide as an oxidant in water. Tungstophosphoric acid (HPW) was found to be active for this transformation due to its ubiquitous catalytic and oxidative nature, and further combination of tetrabutylammonium bromide (TBAB) made this transformation more efficient and attractive. It was found that the yields of the corresponding 2‐substituted imidazolines were markedly influenced by the position and nature of the substituents on the phenyl ring. A plausible mechanism was also proposed to clarify this catalytic oxidative system.

DIFFERENTIAL AND THERMAL ANALYSIS OF COMPLEX CATALYTIC SYSTEM OF TYPE хСrРО4уNi3(РО4)2

Individual phosphates of cobalt and nickel and seven new complex oxide catalytic systems based on chromium phosphate were synthesized by modifying it with ions of Nі2+ type xCrPO4´yNi3(PO4)2 with different content of both phosphates having acidic surface properties. The modern methods of analysis have studied the composition, structure and some physical and chemical parameters of all synthesized samples. The influence of the synthesis conditions on the nature of the formation of their structure and the corresponding physico-chemical and catalytic properties was studied with the help of differential-thermal analysis. It is established that for synthesized binary samples, various forms of water that are part of their composition are characteristic: adsorbed, structural, crystallization, constitutional, etc. Allocating them from the structure of catalysts in the process of heat treatment is accompanied by various effects and corresponding endo-effects. In this case, the kinetics of water thermosorption from the surface and from the volume of internal pores depends on the nature of the interaction between the molecules in the adsorption layers and water molecules on the surface. In the allocation of adsorbed water from phosphate catalysts, the change in the type of anion is not observed. However, the elimination of crystallization, and especially constitutional water, is accompanied by a rupture of chemical bonds, intense diffusion of water vapor from the lattice and rearrangement of phosphate anion. All synthesized phosphates have different curves of DTA, which are different from individual phosphates of cromium and nickel, and with each other. After calcining at 700°C and at higher temperatures, all synthesized complex catalytic phosphate systems exist in the form of anhydrous salts, which is confirmed by the data of X-ray diffraction, IR spectroscopic and chemical analyzes. Thus, the results obtained are in good agreement with [24, 25] and show that, as it was predicted, when changing the composition of the chromium-nickel-phosphate system, it was possible to obtain catalysts, on the surface of which formed certain chemical structures that could form the corresponding optimal surface complexes and detect special catalytic properties in the processes of partial oxidation of n-alkanes in valuable products.

Heme and Nonheme High-Valent Iron and Manganese Oxo Cores in Biological and Abiological Oxidation Reactions.

Utilization of O2 as an abundant and environmentally benign oxidant is of great interest in the design of bioinspired synthetic catalytic oxidation systems. Metalloenzymes activate O2 by employing earth-abundant metals and exhibit diverse reactivities in oxidation reactions, including epoxidation of olefins, functionalization of alkane C–H bonds, arene hydroxylation, and syn-dihydroxylation of arenes. Metal–oxo species are proposed as reactive intermediates in these reactions. A number of biomimetic metal–oxo complexes have been synthesized in recent years by activating O2 or using artificial oxidants at iron and manganese centers supported on heme or nonheme-type ligand environments. Detailed reactivity studies together with spectroscopy and theory have helped us understand how the reactivities of these metal–oxygen intermediates are controlled by the electronic and steric properties of the metal centers. These studies have provided important insights into biological reactions, which have contributed to the design of biologically inspired oxidation catalysts containing earth-abundant metals like iron and manganese. In this Outlook article, we survey a few examples of these advances with particular emphasis in each case on the interplay of catalyst design and our understanding of metalloenzyme structure and function.

Preliminary investigation of the degradation mechanism of o, m and p-cresol using sludge-derived carbon nanosheets by catalytic oxidation based on quantum chemistry

Advanced oxidation technology is widely used to oxidize organic compounds in the liquid phase by OH conventionally. Here, we prepared a sludge-derived carbon nanosheets, which was applied in the catalytic wet air oxidation (CWAO), catalytic wet peroxide oxidation (CWPO) and catalytic wet ozone oxidation (CWOO) systems. Because of its abundant oxygen-containing functional groups, the catalytic activity of nanosheets was much higher than some conventional catalysts. It was found that the first-order reaction model did not have similar characteristics as expected. Combining with molecular descriptors calculated by the DFT method and PLS analysis, we try to explain this phenomenon for the first time and proposed possible mechanisms for the three advanced oxidation technologies.

Peroxymonosulfate activation by iron(III)-tetraamidomacrocyclic ligand for degradation of organic pollutants via high-valent iron-oxo complex

Herein, we proposed a new catalytic oxidation system, i.e., iron(III)-tetraamidomacrocyclic ligand (FeIII-TAML) mediated activation of peroxymonosulfate (PMS), for highly efficient organic degradation using p-chlorophenol (4-CP) as a model one. PMS/FeIII-TAML is capable of degrading 4-CP completely in 9 min at the initial 4-CP of 50 μM and pH = 7, whereas the recently explored system, H2O2/FeIII-TAML, could only result in ∼22% 4-CP removal in 20 min under otherwise identical conditions. More attractively, inorganic anions (i.e., Cl−, SO42−, NO3−, and HCO3−) exhibited insignificant effect on 4-CP degradation, and the negative effect of natural organic matters (NOM) on the degradation of 4-CP in PMS/FeIII-TAML is much weaker than the sulfate radical-based oxidation process (PMS/Co2+). Combined with in-situ XANES spectra, UV-visible spectra, electron paramagnetic resonance (EPR) spectra, and radical quenching experiments, high-valent iron-oxo complex (FeIV(O)TAML) instead of singlet oxygen (1O2), superoxide radical (O2•−), sulfate radicals (SO4•−) and hydroxyl radicals (HO•) was the key active species responsible for 4-CP degradation. The formation rate (kI) and consumption rate (kII) of the FeIV(O)TAML in PMS/FeIII-TAML were pH-dependent in the range of 6.0–11.5. As expected, increasing the FeIII-TAML and PMS dosage resulted in a higher steady-state concentration of FeIV(O)TAML and enhanced the 4-CP degradation accordingly. In addition, the oxidation capacity of PMS was almost totally utilized in PMS/FeIII-TAML for 4-CP oxidation due to the two-electron abstraction from 4-CP by one PMS. We believe this study will shed new light on effective PMS activation by Fe-ligand complexes to efficiently degrade organic contaminants via nonradical pathway.

Polyoxometalate-based ionic liquid catalyst with unprecedented activity and selectivity for oxidative desulfurization of diesel in [Omim]BF4

In this study, a novel Polyoxometalate (POM)-based ionic liquid (IL), [3-(pyridine-1-ium-1-yl)propane-1-sulfonate]3(NH4)3Mo7O24·4H2O, abbreviated [PyPS]3(NH4)3Mo7O24, was prepared and employed as a catalyst in the extraction and catalytic oxidative desulfurization (ECODS) of model and actual diesel. The catalyst was characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analyses (TG-DTA) and X-ray photoelectron spectroscopy (XPS). The [PyPS]3(NH4)3Mo7O24 catalyst demonstrates unprecedented activity in oxidative desulfurization system that the removal of dibenzothiophene (DBT) could reach 99% under quite mild conditions (T = 25 °C, n(catalyst) = 0.0056 mmol, t = 60 min, n(H2O2)/n(sulfur) = 3, VIL/VModel Oil = 1/10). Moreover, the catalytic oxidative desulfurization system can work under the extreme reaction condition, i.e., the DBT removal could reach 99% even at 0 °C. Some important parameters which affect the ODS process, such as temperature, hydrogen peroxide dosage reaction systems and different sulfur compounds, were systematically studied. In addition, the catalyst exhibits remarkable selectivity to the catalytic oxidation sulfides compared with monocyclic or di-aromatics. And this desulfurization system could be recycled for five times without significant reducing the desulfurization. Furthermore, the deep catalytic oxidative desulfurization of actual diesel could also be achieved with this oxidative desulfurization system.

Mineralization of quinoline in aqueous solution by microwave-assisted catalytic wet peroxide oxidation system: process optimization, products analysis and degradation route research.

The experimental design methodology was used to optimize the experimental parameters of quinoline mineralization by microwave-enhanced catalytic wet peroxide oxidation (CWPO). Initial pH value, temperature, H2O2 dosage, and microwave power were selected as independent variables. The mineralization efficiency approached 83.82% under the optimized conditions: initial pH 6.00, temperature 60 °C, H2O2 dosage 0.09 mol/L, and microwave power 565.10 W. Regression analysis with an R2 value of 0.9867 showed a good agreement between the experimental results and the predicted values. Furthermore, based on the detection and identification of products by gas chromatography mass spectrometry, the oxidation degradation pathways of quinoline were proposed. The energy balance and costs analysis indicated that the total cost of the microwave-enhanced CWPO process for wastewater treatment was 40.60 yuan/m3.

Substrate-Controlled Generation of 3-Sulfonylated 1-Indenones and 3-Arylated ( Z)-Indenes via Cu-Catalyzed Radical Cyclization Cascades of o-Alkynylbenzonitriles.

Substrate-controlled generation of 3-sulfonylated 1-indenones and 3-arylated ( Z)-indenes through radical cyclization cascades of o-alkynylbenzonitriles with sulfonyl hydrazides was established by combining copper(II) with tert-butyl hydroperoxide (TBHP) as a catalytic oxidative system. With the installation of the aryl group (R1) into the alkynyl unit, sulfonyl radicals triggered addition-cyclization cascades to access 3-sulfonylated 1-indenones with good yields by using a Cu/TBHP system, whereas a series of new functionalized 3-arylated ( Z)-indenes were obtained in good yields when o-alkynylbenzonitriles bearing the alkyl group in the alkynyl unit were subjected with arylsulfonyl hydrazides with an electron-rich nature under the above conditions.

Syntheses and ultra-deep desulfurization performance of sandwich-type polyoxometalate-based TiO2 nanofibres

The sandwich-type polyoxometalate-based TiO2 nanofibres were prepared successfully by electrospinning combining with chemical reaction and employed in ultra-deep desulfurization. OTA–CoVW–TiO2 nanofibres (OTA = CH3(CH2)17(CH3)3N, CoVW = [Co4(H2O)2(VW9O34)2]10−) confirmed the excellent desulfurization performance in extraction catalytic oxidative desulfurization system (ECODS). At 323 K, the 500 ppm DBT (dibenzothiophene) model oil was entirely removed within 20 min using 0.010 g 45 wt% OTA–CoVW–TiO2 nanofibres as catalyst when O/S molar ratio was 4:1 and the dosage of model oil was 5 mL. The catalysts could be recycled and reused at least five times without remarkable decrease in catalytic activity. The desulfurization efficiencies for different substrates were shown as following order: DBT > 4,6-DMDBT (4,6-dimethyl-dibenzothiophene) > BT (benzothiophene). Moreover, the possible mechanism was also elucidated.

Synthesis of 3-Sulfenylindoles from Indoles and Various Sulfenylation Agents through Aerobic Oxidative C–S Bond Coupling

A novel aerobic catalytic oxidation system for the sulfenylation of indoles with a variety of sulfenylation agents through oxidative C–S bond coupling has been successfully developed. The reactions were performed with potassium iodide as the catalyst, sodium nitrite as the co-catalyst, and molecular oxygen as the terminal oxidant in the presence of acetic acid. Under the optimal reaction conditions, a number of indoles could be sulfenylated with Bunte salts, thiols, or disulfides to generate 3-sulfenylindoles in good yields. This protocol provided an efficient and environmentally benign strategy for the synthesis of 3-sulfenylindoles.