Distribution Of Oxidation Products Research Articles

Hierarchical H-MOR Zeolite Supported Vanadium Oxide for Dimethyl Ether Direct Oxidation

A series of hierarchical H-MOR zeolites with different pore structure were designed and synthesized by alkaline and alkaline-acid post-synthesis methods. The catalytic performance of hierarchical H-MOR zeolite-supported vanadium oxide was investigated for dimethyl ether (DME) direct oxidation. Different pore structures apparently affect the distribution of oxidation product distribution, especially the selectivity of DMMx and CO. The formation of mesopores for 10%V2O5/deAlmm-H-MOR markedly improved the DMMx selectivity up to 78.2% from 60.0%, and more notably, CO selectivity dropped to zero compared to that of 10%V2O5/H-MOR. The hierarchical H-MOR zeolites were confirmed to be successfully prepared by the post-synthesis method. Due to the presence of mesoporous structure, the dispersion of vanadium oxide species was enhanced, which could improve the reducibility of vanadium oxide species and also make better contact with the acid sites of zeolite to exert the synergistic effect of the bifunctional active sites. More importantly, the creation of mesopores was proved to be favorable to the mass transfer of intermediate and products to avoid the occurrence of secondary reaction, which could effectively suppress the formation of by-products. This work is helpful for us to provide a novel insight to design the catalyst with suitable pore structure to effectively synthesize diesel fuel additives from DME direct oxidation.

Catalytic performance of TS-1 in oxidative cleavage of 1-alkenes with H2O2

Trace dimethoxymethane (DMM) was formed by aldol condensation of formaldehyde with methanol in industrial propene oxide production via a hydrogen peroxide (HPPO process). Probing the behaviour of catalytic action in oxidative cleavage reaction of CC bond of alkene is urgently needed for the development of production technology. Using 1-hexene as a probe, the oxidation of alkenes with H2O2 was investigated via titanium silicalite-1 (TS-1) catalysis. Influences of solvent, temperature, additives and H2O2/alkene molar ratio on alkene conversion and oxidation product distribution were studied. Interestingly, besides the epoxidation products, aldehydes were also produced by double-bond oxidative cleavage in this system. The results showed that ethyl acetate as solvent was favor for the generation of aldehyde, but the additives [Na2HPO4·12H2O (A) and NaH2PO4(B)] could significantly inhibit it. These phenomena indicated that the catalytic oxidative cleavage of 1-hexene in TS-1/H2O2 system was probably based on an addition and cleavage oxidation process in an acidic environment.

Correlation between Copper Oxide Particle Size and Selectivity towards Propylene Oxide in Selective Oxidation of Propene

AbstractCopper oxide catalysts supported on nanostructured silica SBA‐15 were synthesized with varying copper loadings in a range from 1.1 to 19.4 wt.%. Catalysts were structurally characterized by N2 physisorption, X‐ray diffraction and ex situ as well as in situ diffuse reflectance UV‐Vis spectroscopy. Copper oxide species contained Cu2+ in an octahedral configuration with a tetragonal distortion. Increasing the copper loading resulted in a decreasing optical band gap, which is associated with a growing particle size. Additionally, CuO/SBA‐15 samples were examined by temperature‐programmed reduction confirming a narrow particle size distribution. Structural evolution and catalytic activity were investigated during selective oxidation of propene focusing on product distribution of nucleophilic and electrophilic oxidation. Catalytic testing was carried out using an on‐line GC and MS coupled to a laboratory fixed‐bed reactor. All catalysts selectively oxidized propene to acrolein and propylene oxide (PO). With time on stream activity decreased while selectivity towards acrolein and PO increased. While selectivity towards PO increased with copper loading and, hence, copper oxide particle size, selectivity towards acrolein was largely independent of copper loading.

Analysis of the Fundamental Aspects of Oxidation of Rich Methane Mixtures in Matrix-Type Converters

Equilibrium distribution of oxidation products was calculated for the system СН4 + ψО2 → products at 0.5 0.6 and temperatures higher than 1000–1200 K (depending on ψ), when there is no Csolid in the system; and II, if this component is present in the system. The range of working temperatures and values of ψ, at which the matrix conversion process occurs, falls within region I. A nearly 100% conversion of oxygen and methane is reached within this region; there is no Csolid; and CO, H2, CO2, and H2O are products of the partial oxidation of methane in equilibrium. The temperature limits within which the system passes into region II and the formation of the synthesis gas is accompanied by the appearance of soot were determined. Formulas describing the dependence of the yield of oxidation products per mole of converted methane at various ratios between the methane and oxygen concentrations were derived. An expression was obtained on the basis of experimental data, which can be used to approximately calculate to within <6% the most important technological parameter of the matrix conversion process, [H2]/[CO] ratio.

Sustainable Conversion of Glycerol into Value‐Added Chemicals by Selective Electro‐Oxidation on Pt‐Based Catalysts

AbstractThe front cover artwork is provided by Shen's group from the South China University of Technology (China). The image shows glycerol electro‐oxidation over a series of Pt‐based catalysts in alkaline solutions. The activity and product distribution of glycerol oxidation could be optimized by tuning the catalyst composition and the applied potentials. Read the full text of the Article at 10.1002/celc.201800309.

Molecular Distributions of Soluble Oxidation Products from Coals Characterized by Mass Spectrometers.

Oxidation of three coals with rank from lignite to anthracite in NaOCl aqueous solution was investigated in this study. The oxidation products were characterized by using gas chromatography/mass spectrometry and direct analysis in real-time mass spectrometry. The results showed that most of organic compounds in coals were converted into water-soluble species under mild conditions, even the anthracite. Benzene polycarboxylic acids (BPCAs) and chloro-substituted alkanoic acids (CSAAs) were major products from the reactions. The products from lower rank coals consist of considerable CSAAs and most products from high rank coals are BPCAs. As coal rank increases, the yield of BPCAs with more carboxylic groups increases.

Oxidation of benzoic acid by heat-activated persulfate: Effect of temperature on transformation pathway and product distribution

Heat activates persulfate (S2O82−) into sulfate radical (SO4−), a powerful oxidant capable of transforming a wide variety of contaminants. Previous studies have shown that an increase in temperature accelerates the rates of persulfate activation and contaminant transformation. However, few studies have considered the effect of temperature on contaminant transformation pathway. The objective of this study was to determine how temperature (T = 22–70 °C) influences the activation of persulfate, the transformation of benzoic acid (i.e., a model compound), and the distribution of benzoic acid oxidation products. The time-concentration profiles of the products suggest that benzoic acid was transformed via decarboxylation and hydroxylation mechanisms, with the former becoming increasingly important at elevated temperatures. The pathway through which the products were further oxidized was also influenced by the temperature of persulfate activation. Our findings suggest that the role of temperature in the persulfate-based treatment systems is not limited only to controlling the rates of sulfate and hydroxyl radical generation. The ability of sulfate radical to initiate decarboxylation reactions and, more broadly, fragmentation reactions, as well as the effect of temperature on these transformation pathways could be important to the transformation of a number of organic contaminants.

Isomerization of Second-Generation Isoprene Peroxy Radicals: Epoxide Formation and Implications for Secondary Organic Aerosol Yields

We report chamber measurements of secondary organic aerosol (SOA) formation from isoprene photochemical oxidation, in which radical concentrations were systematically varied and the molecular composition of semi- to low-volatility gases and SOA were measured online. Using a detailed chemical kinetics box model, we find that to explain the behavior of low-volatility products and SOA mass yields relative to input H2O2 concentrations, the second-generation dihydroxy hydroperoxy peroxy radical (C5H11O6·) must undergo an intramolecular H-shift with a net forward rate constant of order 0.1 s-1 or higher. This finding is consistent with quantum chemical calculations that suggest a net forward rate constant of 0.3-0.9 s-1. Furthermore, these calculations suggest that the dominant product of this isomerization is a dihydroxy hydroperoxy epoxide (C5H10O5), which is expected to have a saturation vapor pressure ∼2 orders of magnitude higher, as determined by group-contribution calculations, than the dihydroxy dihydroperoxide, ISOP(OOH)2(C5H12O6), a major product of the peroxy radical reacting with HO2. These results provide strong constraints on the likely volatility distribution of isoprene oxidation products under atmospheric conditions and, thus, on the importance of nonreactive gas-particle partitioning of isoprene oxidation products as an SOA source.

Effect of nitrogen doping on the catalytic activity of activated carbon and distribution of oxidation products in catalytic wet oxidation of phenol

AbstractNitrogen‐containing functional groups were introduced into activated carbon (AC) by amination at high temperatures to investigate their effects on the catalytic activity and distribution of products in the catalytic wet air oxidation (CWAO) of phenol at 120 and 160 °C. The results show that the catalytic activity of the nitrogen‐doped AC increases with amination temperature from 250 to 850 °C. The linear relationship between the quantity of nitrogen‐containing functional groups and the catalytic activity indicates that the enhanced activities are closely related to the amount of pyridinic and pyrrolic nitrogen groups on the surface of the AC. The parent and aminated AC exhibit distinct distributions of oxidation products. Oxalic acid is favourably degraded on the aminated AC, whereas the all‐carbon AC shows a similar ability for the removal of acetic acid.

The oxidative decomposition of natural bioactive compound rhamnetin

The oxidation of the natural bioflavonoid rhamnetin was studied by a multi-analytical approach. It was widely used as a dye for colouring tapestries, and it is known for degrading in the presence of atmospheric oxygen and light. The oxidation mechanism was studied by cyclic voltammetry and UV–Vis spectroelectrochemical methods in aqueous solution on glassy carbon and platinum electrodes. Two-electron and two-proton oxidation proceeds in acidic solution, while two-electron and one-proton oxidation was found for a dissociated molecule of rhamnetin, and one electron oxidative process was obtained for the dianion present in alkaline solution. The complicated oxidation mechanism involves not only electron transfer, but also several coupled chemical reactions. The products were identified by HPLC-DAD and HPLC-ESI-MS/MS techniques. The distribution of oxidation products was strongly dependent on the duration of exposure to atmospheric oxygen. The main oxidation product was identified as 2-[(3,4-dihydroxyphenyl)carbonyl]-2,4-dihydroxy-6-methoxy-1-benzofuran-3(2H)-one. Because rhamnetin in solution was fully degraded by oxygen in 6min, it was necessary to prepare its solutions under argon atmosphere prior any electrochemical measurement.

Characterisation of two self-sufficient CYP102 family monooxygenases from Ktedonobacter racemifer DSM44963 which have new fatty acid alcohol product profiles

BackgroundTwo self-sufficient CYP102 family encoding genes (Krac_0936 and Krac_9955) from the bacterium Ktedonobacter racemifer DSM44963, which possesses one of the largest bacterial genomes, have been identified. MethodsPhylogenetic analysis of both the encoded cytochrome P450 enzymes, Krac0936 and Krac9955. Both enzymes were produced and their turnovers with fatty acid substrates assessed in vitro and using a whole-cell oxidation system. ResultsKrac0936 hydroxylated straight chain, saturated fatty acids predominantly at the ω-1 and ω-2 positions using NADPH as the cofactor. Krac0936 was less active towards shorter unsaturated fatty acids but longer unsaturated acids were efficiently oxidised. cis,cis-9,12-Octadecadienoic and pentadecanoic acids were the most active substrates tested with Krac0936. Unusually Krac9955 showed very low levels of NAD(P)H oxidation activity though coupling of the reducing equivalents to product formation was high. The product distribution of tridecanoic, tetradecanoic and pentadecanoic acid oxidation by Krac9955 favoured oxidation at the ω-4, ω-5 and ω-6 positions, respectively. ConclusionKrac0936 and Krac9955 are self-sufficient P450 monooxygenases. Krac0936 has a preference for pentadecanoic acid over other straight chain fatty acids and showed little or no activity with dodecanoic or octadecanoic acids. Krac9955 preferably oxidised shorter fatty acids compared to Krac0936 with tridecanoic having the highest levels of product formation. Unlike Krac0936 and P450Bm3, Krac9995 showed lower activities with unsaturated fatty acids. General significanceIn this study of two of the CYP enzymes from K. racemifer we have shown that this bacterium from the Chloroflexi phylum contains genes which encode new proteins with novel activity.

Degradation of cable insulation material by accelerated thermal radiation combined ageing

The degradation of ethylene propylene rubber (EPR) sheets as a cable insulation material for nuclear power plants (NPP) was studied by accelerated thermal ageing, radiation ageing and thermal – radiation combined ageing. The oxidation of EPR proceeded with ageing and the decay of mechanical property was closely related to the content of oxidation products. The antioxidant as a stabilizer in EPR was effective for the thermal oxidation, but not for the radiation oxidation. The distribution of oxidation products across the sheet was changed due to decay of antioxidant by evaporation during thermal ageing. The antioxidant was not effective for radiation oxidation, and it was decomposed by radiation. For the thermal and radiation combined oxidation, the mechanical property and the content of oxidation products were different among the treatment sequences, which was due to the decay of antioxidant. The lifetime of EPR cable is closely related to the remaining content of antioxidant, and the lifetime evaluation would be recommended by the reverse sequential combination (thermal ageing after radiation ageing).

A numerical procedure for simulating thermal oxidation diffusion of epoxy molding compounds

A new numerical procedure is developed for simulating the thermal oxidation diffusion of epoxy molding compounds (EMC). In this approach, the formal similarity of oxidation diffusion equation and the heat conduction equation is utilized to convert the oxidation diffusion issue to heat conduction issue, then a 2D finite element model of EMC is established, and the oxidation diffusion of EMC aged under 150°C is implemented with the thermal conduction modules of software ANSYS. The concentration distribution of oxidation products and the distribution of elastic modulus are calculated in ANSYS in the oxidized layer after 100h, 600h and 1000h of isothermal aging at 150°C under atmospheric air. The comparison between the calculated results and the simulated and experimental data obtained from literature is conducted. Moreover, the influence of silica filler in EMC on the oxidation diffusion is analyzed preliminarily. The results indicate that the oxidation diffusion can be effectively simulated, and the fillers in EMC probably affect the oxidation diffusion process. Evidently, the proposed procedure is effective for simulating the issues of thermal oxidation of EMC, while further experimental validations are needed.

Application of high-resolution time-of-flight chemical ionization mass spectrometry measurements to estimate volatility distributions of α-pinene and naphthalene oxidation products

Abstract. Recent developments in high-resolution time-of-flight chemical ionization mass spectrometry (HR-ToF-CIMS) have made it possible to directly detect atmospheric organic compounds in real time with high sensitivity and with little or no fragmentation, including low-volatility, highly oxygenated organic vapors that are precursors to secondary organic aerosol formation. Here, using ions identified by high-resolution spectra from an HR-ToF-CIMS with acetate reagent ion chemistry, we develop an algorithm to estimate the vapor pressures of measured organic acids. The algorithm uses identified ion formulas and calculated double bond equivalencies, information unavailable in quadrupole CIMS technology, as constraints for the number of possible oxygen-containing functional groups. The algorithm is tested with acetate chemical ionization mass spectrometry (acetate-CIMS) spectra of O3 and OH oxidation products of α-pinene and naphthalene formed in a flow reactor with integrated OH exposures ranged from 1.2 × 1011 to 9.7 × 1011 molec s cm−3, corresponding to approximately 1.0 to 7.5 days of equivalent atmospheric oxidation. Measured gas-phase organic acids are similar to those previously observed in environmental chamber studies. For both precursors, we find that acetate-CIMS spectra capture both functionalization (oxygen addition) and fragmentation (carbon loss) as a function of OH exposure. The level of fragmentation is observed to increase with increased oxidation. The predicted condensed-phase secondary organic aerosol (SOA) average acid yields and O/C and H/C ratios agree within uncertainties with previous chamber and flow reactor measurements and ambient CIMS results. While acetate reagent ion chemistry is used to selectively measure organic acids, in principle this method can be applied to additional reagent ion chemistries depending on the application.

Direct catalytic oxidation of lower alkanes in ionic liquid media

Immobilization of rhodium (palladium)-copper-chloride catalytic systems in ionic liquids as high-boiling-point solvents affects the distribution of propane oxidation products: the acetone yield increases and the yield of alcohols decreases. Propane is oxidized to acetone, bypassing the isopropanol formation step. Methane is oxidized under more severe conditions than propane, giving methyl trifluoroacetate as the main product. Mechanisms of action of the catalytic systems based on rhodium and palladium are close to each other and likely include oxo or peroxo complexes as intermediates.

Hydroxyl-radical-induced oxidation of 5-methylcytosine in isolated and cellular DNA.

The methylation and oxidative demethylation of cytosine in CpG dinucleotides plays a critical role in the regulation of genes during cell differentiation, embryogenesis and carcinogenesis. Despite its low abundance, 5-methylcytosine (5mC) is a hotspot for mutations in mammalian cells. Here, we measured five oxidation products of 5mC together with the analogous products of cytosine and thymine in DNA exposed to ionizing radiation in oxygenated aqueous solution. The products can be divided into those that arise from hydroxyl radical (•OH) addition at the 5,6-double bond of 5mC (glycol, hydantoin and imidazolidine products) and those that arise from H-atom abstraction from the methyl group of 5mC including 5-hydroxymethylcytosine (5hmC) and 5-formylcytosine (5fC). Based on the analysis of these products, we show that the total damage at 5mC is about 2-fold greater than that at C in identical sequences. The formation of hydantoin products of 5mC is favored, compared to analogous reactions of thymine and cytosine, which favor the formation of glycol products. The distribution of oxidation products is sequence dependent in specific ODN duplexes. In the case of 5mC, the formation of 5hmC and 5fC represents about half of the total of •OH-induced oxidation products of 5mC. Several products of thymine, cytosine, 5mC, as well as 8-oxo-7,8-dihydroguanine (8oxoG), were also estimated in irradiated cells.

From multispectral imaging of autofluorescence to chemical and sensory images of lipid oxidation in cod caviar paste

The potential of multispectral imaging of autofluorescence to map sensory flavour properties and fluorophore concentrations in cod caviar paste has been investigated. Cod caviar paste was used as a case product and it was stored over time, under different headspace gas composition and light exposure conditions, to obtain a relevant span in lipid oxidation and sensory properties. Samples were divided in two sets, calibration and test sets, with 16 and 7 samples, respectively. A third set of samples was prepared with induced gradients in lipid oxidation and sensory properties by light exposure of certain parts of the sample surface. Front-face fluorescence emission images were obtained for excitation wavelength 382 nm at 11 different channels ranging from 400 to 700 nm. The analysis of the obtained sets of images was divided in two parts: First, in an effort to compress and extract relevant information, multivariate curve resolution was applied on the calibration set and three spectral components and their relative concentrations in each sample were obtained. The obtained profiles were employed to estimate the concentrations of each component in the images of the heterogeneous samples, giving chemical images of the distribution of fluorescent oxidation products, protoporphyrin IX and photoprotoporphyrin. Second, regression models for sensory attributes related to lipid oxidation were constructed based on the spectra of homogeneous samples from the calibration set. These models were successfully validated with the test set. The models were then applied for pixel-wise estimation of sensory flavours in the heterogeneous images, giving rise to sensory images. As far as we know this is the first time that sensory images of odour and flavour are obtained based on multispectral imaging.

Multifunctionality of Crystalline MoV(TeNb) M1 Oxide Catalysts in Selective Oxidation of Propane and Benzyl Alcohol

Propane oxidation at 653–673 K and benzyl alcohol oxidation at 393 K over phase-pure MoV(TeNb) M1 oxide catalysts were studied to gain insight into the multiple catalytic functions of the surface of the M1 structure. Electron microscopy and X-ray diffraction confirmed the phase purity of the M1 catalysts. Propane oxidation yields acrylic acid via propene as intermediate, while benzyl alcohol oxidation gives benzaldehyde, benzoic acid, benzyl benzoate, and toluene. The consumption rates of benzyl alcohol and propane level in the same range despite huge difference in reaction temperature, suggesting high activity of M1 for alcohol oxidation. Metal–oxygen sites on the M1 surface are responsible for the conversion of the two reactants. However, different types of active sites and reaction mechanisms may be involved. Omitting Te and Nb from the M1 framework eliminates acrylic acid selectivity in propane oxidation, while the product distribution in benzyl alcohol oxidation remains unchanged. The results suggest...

On the factors affecting product distribution in laccase-catalyzed oxidation of a lignin model compound vanillyl alcohol: experimental and computational evaluation

Laccases (EC 1.10.3.2) are multicopper oxidases, which can oxidize phenolic substrates by the concomitant reduction of oxygen to water. The phenolic substructures of lignin are also oxidized by laccases, resulting mainly in various polymerized products. Several model compound studies indicate that variations in the reaction media, such as the pH and the enzyme dosage used, have an impact on the observed product distribution of laccase promoted oxidation, but no detailed study has been reported to explain these results. In the present study, a monomeric lignin model compound, vanillyl alcohol, was oxidized in laccase-catalyzed reactions by varying the pH, enzyme dosage and temperature. The energies of all the observed products and potential intermediates were calculated by applying density functional theory (DFT) and the polarizable continuum solvation model (PCM). The observed predominant product at pH 4.5 to 7.5 was clearly the 5-5' dimer, although the thermodynamic product according to the calculated free energies was vanillin, the difference being 5.6 kcal mol(-1). The hydrogen bonding is shown to give an additional stabilizing effect on the transition state leading to the 5-5' dimer, but also a kinetic barrier reduces the formation of vanillin. Based on the calculated pKa-values of the proposed intermediates we suggest that the rearomatization reactions of the quinones formed in the radical reactions under mildly acidic and neutral conditions would preferentially occur through deprotonation rather than through protonation.

Distribution of Protein Oxidation Products in the Proteome of Thermally Processed Milk

During thermal milk processing, severe oxidation can occur, which alters the technological and physiological properties of the milk proteins. Due to differences in composition and physicochemical properties, it can be expected that the particular milk proteins are differently affected by oxidative damage. Therefore, the protein-specific distribution of oxidation products in the heated milk proteome was investigated. Raw and heated milk samples were separated by one-dimensional gel electrophoresis. Protein oxidation was visualized by Western blot after derivatization of protein carbonyls with 2,4-dinitrophenylhydrazine. Thus, α-lactalbumin displayed enhanced oxidation compared to β-lactoglobulin, despite its lower concentration in milk. Highly selective oxidation was detected for a previously unassigned minor milk protein. The protein was identified by its peptide mass fingerprint as a variant of α(S1)-casein (α(S1)-casein*). Similar oxidation patterns were observed in several commercial milk products.