Hydrocarbon Oxidation Reactions Research Articles

Synergetic effect of Pd addition on catalytic behavior of monolithic platinum–manganese–alumina catalysts for diesel vehicle emission control

The advanced diesel emission control catalyst Pt–Pd–MnOx–Al2O3 has been developed on the basis of the synergetic effect of Pt with Pd and manganese oxides observed in hydrocarbon and carbon monoxide oxidation reactions. This effect allows a decrease in the total loadings of Pt and Pd down to 0.52g/L in the monolithic catalyst, providing high activity in low temperature oxidation of light hydrocarbons and high thermal stability.The catalytic activity of Pt–Pd–MnOx–Al2O3 monolithic catalysts in butane oxidation and DIESEL tests depends on the Pt and Pd precursors, their individual loadings and their ratio (Pt/Pd). For a selected Pt precursor at its content 0.17g/L, the catalytic performance of Pt–Pd–MnOx–Al2O3 catalyst improves with an increase in Pd loading from 0 to 0.35g/L and is nearly constant at a higher Pd loading (0.70g/L). The most active monolithic Pt–Pd–MnOx–Al2O3 catalyst is prepared by using platinum-dinitrodiamine and palladium nitrate solutions as noble metal precursors.The catalytic activity in light hydrocarbon oxidation is shown to correlate with the RedOx properties of PdPt–MnOx–Al2O3 catalysts and the Pt–Pd particle size. The non-additive increase in the catalytic activity of bimetallic catalyst is suggested to connect with a formation of nanoscale PdO–PtOx particles on the surface of Mn3O4 and a modification of alumina structure by Mn3+ and PtPd clusters.

Novel nickel(II) and manganese(III) complexes with bidentate Schiff-base ligand: synthesis, spectral, thermogravimetry, electrochemical and electrocatalytical properties

An unsymmetrical bidentate Schiff base ligand, ethane 2-(4-methoxyphenyl)-1-iminosalicylidene, and its novel two mononuclear complexes, Nickel(II) [Ni(II)-2L] and Manganese(III) [Mn(III)Cl-2L] where L represents the ligand, have been synthesized and characterized by various physicochemical methods. The Ni(II) ion is coordinated by two nitrogen and two oxygen atoms with both the bidentate Schiff base ligands in an approximately square planar coordination geometry, while the manganese complex, the Mn(III) ion, is involved in an additional contact with one chloride anion for which the coordination sphere appears as a square pyramidal arrangement. The thermogravimetric analyses of the synthesized compounds revealed three different stages of decomposition for NONO bis-bidentate manganese and nickel complexes. The cyclic voltammetry studies of these complexes in N,N-dimethylformamide showed a redox couple for each one of them, such as Ni(II)/Ni(I) and Mn(III)/Mn(II), which are quasi-reversible. Their catalytic behaviors were tested showing that the nickel complex is an effective electrocatalyst in the reduction of bromocyclopentane. Regarding the manganese complex, it was revealed that it is an efficient catalyst in the activation of molecular dioxygen, currently applied in oxidation reactions of hydrocarbons according to the monooxygenase enzymes as those of cytochrome P450 model.

Structured woven glass-fiber IC-12-S111 catalyst for the deep oxidation of organic compounds

A platinum woven fiberglass supported IC-12-S111 catalyst whose preparation is based on pulsed surface thermosynthesis is developed. The IC-12-S111 catalyst contains small amounts of platinum (0.05–0.10 wt %), and cheap and commercially available types of fiberglass cloths are used in its production. The production technology is characterized by a small number of process stages and no wastes or platinum losses. The developed catalyst is superior to known platinum and oxide catalysts in its activity in the deep oxidation reactions of hydrocarbons, and exhibits high thermal and operational stability. IC-12-S111 based catalytic cartridges with regularly structured channels are characterized by low hydraulic resistance and minimize deposits of solid particles in a catalyst bed during operation in contaminated flows. The cartridges can be used to create beds of any size and configuration. The developed catalyst can be used for the afterburning of hydrocarbons and organic compounds in flue gases, the flameless oxidation of flare gases, and the catalytic combustion of hydrocarbon fuels in local power supply systems.

Practical hyperdynamics method for systems with large changes in potential energy.

A practical hyperdynamics method is proposed to accelerate systems with highly endothermic and exothermic reactions such as hydrocarbon pyrolysis and oxidation reactions. In this method, referred to as the "adaptive hyperdynamics (AHD) method," the bias potential parameters are adaptively updated according to the change in potential energy. The approach is intensively examined for JP-10 (exo-tetrahydrodicyclopentadiene) pyrolysis simulations using the ReaxFF reactive force field. Valid boost parameter ranges are clarified as a result. It is shown that AHD can be used to model pyrolysis at temperatures as low as 1000 K while achieving a boost factor of around 10(5).

Cofactor-free light-driven whole-cell cytochrome P450 catalysis.

Cytochromes P450 can catalyze various regioselective and stereospecific oxidation reactions of non-functionalized hydrocarbons. Here, we have designed a novel light-driven platform for cofactor-free, whole-cell P450 photo-biocatalysis using eosin Y (EY) as a photosensitizer. EY can easily enter into the cytoplasm of Escherichia coli and bind specifically to the heme domain of P450. The catalytic turnover of P450 was mediated through the direct transfer of photoinduced electrons from the photosensitized EY to the P450 heme domain under visible light illumination. The photoactivation of the P450 catalytic cycle in the absence of cofactors and redox partners is successfully conducted using many bacterial P450s (variants of P450 BM3) and human P450s (CYPs 1A1, 1A2, 1B1, 2A6, 2E1, and 3A4) for the bioconversion of different substrates, including marketed drugs (simvastatin, lovastatin, and omeprazole) and a steroid (17β-estradiol), to demonstrate the general applicability of the light-driven, cofactor-free system.

Oxygen-Nonstoichiometric YBaCo4O7+δ as a Catalyst in H2O2 Oxidation of Cyclohexene

Here we present oxygen-nonstoichiometric transition metal oxides as highly prominent candidates to catalyze the industrially important oxidation reactions of hydrocarbons when hydrogen peroxide is employed as an environmentally benign oxidant. The proof-of-concept data are revealed for the complex cobalt oxide, YBaCo4O7+δ (0 60 % conversion) than the commercial TiO2 catalyst (<20 %) even though its surface area was less than one tenth of that of TiO2. In the 7-h experiments with YBaCo4O7+δ, 100 % conversion of cyclohexene was achieved. Immersion calorimetry measurements showed that the high catalytic activity may be ascribed to the exceptional ability of YBaCo4O7+δ to dissociate H2O2 and release active oxygen to the oxidation reaction.

Effect of propene, propane, and methane on conversion and oxidation state of three-way catalysts: a microwave cavity perturbation study

This paper presents laboratory reactor measurements of the steady-state conversion of the pollutants CO, hydrocarbons and NO over a three-way catalyst containing ceria as an oxygen-storage component. It is shown that the presence of the saturated hydrocarbons C3H8 or CH4 causes a shift in the stoichiometry of optimal conversion (CO–NO crossover) to fuel-rich compositions. The shift was more pronounced at lower temperatures and can be explained by the kinetic limitation of the hydrocarbon oxidation reaction. A microwave cavity perturbation technique was used to measure in situ the oxidation state of the ceria. In a first step, titration experiments were performed. The oxygen-storage level was adjusted to a predefined level by equilibration with a H2/H2O mixture. The experiments showed that for a given temperature, the microwave-derived signal (here the resonance frequency) correlates well with the oxidation state of ceria. The microwave cavity perturbation technique was then applied simultaneously to steady-state performance tests in the presence of different hydrocarbons. It was found that if the exhaust stoichiometry is ramped from lean to fuel rich, the CO–NO crossover point in all cases coincides with a strong decrease in the oxidation state of ceria. The correlation between the oxidation state of the catalyst and the catalytic performance is found to be independent of the catalyst temperature and the nature of the hydrocarbon. The CO–NO crossover point can be precisely determined by the microwave cavity perturbation technique. The results suggest that a microwave-based measurement may, under some circumstances, allow for a more precise control of the catalyst performance than the conventional control by lambda sensors.

Carbon nanotubes as catalyst for the aerobic oxidation of cumene to cumene hydroperoxide

The effective oxidation reaction system using the commercial carbon nanotubes (CNTs) as catalysts for the liquid aerobic oxidation of cumene to cumene hydroperoxide (CHP) under low temperature is reported in this paper. Several reaction parameters, including the temperature, catalyst content, oxygen flow rate and reaction time were carefully studied. Under optimal conditions, cumene conversion of 24.1% with CHP selectivity of 88.4%, close to that of metal catalyst, was obtained. Cumene oxidation catalyzed by CNTs was proved a radical-involved reaction, and the outstanding catalytic performance was attributed to CHP decomposition catalyzed by CNTs to produce free radicals. Oxygenated functional groups on the surface of catalyst showed a negative effect on cumene oxidation due to the localization of electrons after the introducing of defects and oxygenated functional groups. CNTs as catalysts also showed desirable recyclability after five cycling tests. This study not only provides an applicable method for selective oxidation of cumene to CHP, but also gives some useful information on catalytic role of CNTs-catalyzed liquid-phase oxidation reactions of aromatic hydrocarbons.

Low-temperature speciation and chemical kinetic studies of n-heptane

Although there have been many ignition studies of n-heptane—a primary reference fuel—few studies have provided detailed insights into the low-temperature chemistry of n-heptane through direct measurements of intermediate species formed during ignition. Such measurements provide understanding of reaction pathways that form toxic air pollutants and greenhouse gas emissions while also providing key metrics essential to the development of chemical kinetic mechanisms. This paper presents new ignition and speciation data taken at high pressure (9atm), low temperatures (660–710K), and a dilution of inert gases-to-molecular oxygen of 5.64 (mole basis). The detailed time-histories of 17 species, including large alkenes, aldehydes, carbon monoxide, and n-heptane were quantified using gas chromatography. A detailed chemical kinetic mechanism developed previously for oxidation of n-heptane reproduced experimentally observed ignition delay times reasonably well, but predicted levels of some important intermediate chemical species that were significantly different from measured values. Results from recent theoretical studies of low temperature hydrocarbon oxidation reaction rates were used to upgrade the chemical kinetic mechanism for n-heptane, leading to much better agreement between experimental and computed intermediate species concentrations. The implications of these results to many other hydrocarbon fuel oxidation mechanisms in the literature are discussed.

Reaction Kinetics of C3H6 Oxidation for Various Reaction Pathways Over Diesel Oxidation Catalysts

Reaction kinetics studies of C3H6 oxidation over Pt/Al2O3 and Pt/SiO2 catalysts were characterized using temperature-programmed oxidation with different oxidants: O2, NO2 and surface nitrates. Activation energies and conversion performance were compared in order to determine which hydrocarbon oxidation reaction pathway(s) is relevant in diesel exhaust gas aftertreatment applications. NO x adsorption did not occur on the SiO2 surface so the reaction between C3H6 and NO2 could be isolated, i.e. no nitrate effect would complicate the analysis and their significance could be decoupled. These results were then compared with Pt/Al2O3 where surface nitrates did form upon exposure to NO x . The onset of C3H6 oxidation was observed at a lower temperature with O2 than with NO2, but the activation energy was lower with NO2. This apparent discrepancy is related to the different oxidant concentrations used and the different adsorption pathways. The results indicate that hydrocarbons must be activated first for oxidation to begin, for either NO2 or O2. In analyzing the reaction between C3H6 and nitrates, the reaction did not occur until NO x started to desorb from the catalyst at higher temperatures, i.e. when nitrates became unstable and decomposed, thus providing a readily available oxidant source. However, when O2 was added to the nitrate/C3H6 system, the reaction began at even lower temperature than with just C3H6 and O2. Nitrate consumption was also observed once oxidation began. The presence of the combination of nitrates and O2 resulted in a lower C3H6 oxidation activation energy.

ChemInform Abstract: Theoretical Studies and Industrial Applications of Oxidative Activation of Inert C—H Bond by Metalloporphyrin‐Based Biomimetic Catalysis

AbstractReview: 162 refs.

Theoretical studies and industrial applications of oxidative activation of inert C-H bond by metalloporphyrin-based biomimetic catalysis

High costs and low catalytic efficiency of metalloporphyrins, which are an analogue of cytochrome P450 enzyme, are the bottlenecks in the industrialization of biomimetic hydrocarbon oxidation reactions. The basic principle and research technique of physical organic chemistry were applied to the process of biomimetic oxidation of hydrocarbon catalyzed by metalloporphyrins. This biomimetic technology could be adapted to bulk chemicals production by developing the new methods for efficient scale-up synthesis of metalloporphyrins, new pathways for molecular oxygen activation on an industrial scale and new approaches to elevate the catalytic efficiency of metalloporphyrins. This review mainly focuses on research carried out in our group.

Iron(III) porphyrin covalently supported onto magnetic amino-functionalized nanospheres as catalyst for hydrocarbon and herbicide oxidations

This work describes the covalent immobilization of an ironporphyrin, 5,10,15,20- tetrakis(pentafluorophenyl)porphyrin iron(III) chloride (FeTFPP), onto maghemite/silica magnetic nanospheres covered with aminofunctionalized silica. The resulting material (γ-Fe2O3/SiO2-NHFeP) was characterized by diffuse reflectance infrared spectroscopy (DRIFTS) and UV-Vis absorption spectroscopy. The catalytic activity of this magnetic ironporphyrin was investigated in the oxidation of hydrocarbons (styrene, (Z)-cyclooctene and R-(+)-limonene) and an herbicide (simazine) by hydrogen peroxide or 3-chloroperoxybenzoic acid. Hydrocarbon and simazine oxidation reaction products were analyzed by gas chromatography (GC) and high performance liquid chromatography (HPLC), respectively. This catalytic system proved to be efficient and selective for hydrocarbon oxidation, leading to high product yields from styrene (89%), cyclooctene (71%) and R-(+)-limonene (86%). Simazine oxidation was attained with 100% selectivity for a dechlorinated product (OEAT), while several oxidation products were obtained for the same catalyst in homogeneous media. The catalyst can be easily recovered through application of an external magnetic field and washed after reaction. Catalyst reuse experiments for R-(+)-limonene oxidation have shown that the catalytic activity is kept at 90% after 10 consecutive reactions.

Takovite–Aluminosilicate–Cr Materials Prepared by Adsorption of Cr3+ from Industrial Effluents As Catalysts for Hydrocarbon Oxidation Reactions

The catalytic efficiency of takovite-aluminosilicate-chromium catalysts obtained by adsorption of Cr(3+) ions from aqueous solutions by a takovite-aluminosilicate nanocomposite adsorbent is reported. The adsorbent was synthesized by the coprecipitation method. The catalytic activity of the final Cr-catalysts depended on the amount of adsorbed chromium. (Z)-cyclooctene conversion up to 90% with total selectivity for the epoxide was achieved when the oxidation was carried out with hydrogen peroxide, at room temperature. After five consecutive runs, the catalysts maintained high activity, although after the sixth reuse, the epoxide yields strongly decreased to 35%. The catalysts were also efficient for cyclohexane oxidation, reaching up to 18% conversion, with cyclohexanone/cyclohexanol selectivity close to 1.2. On the whole, their use as catalysts gives a very interesting application for the solids obtained by adsorption of a contaminant cation such as Cr(3+).

Mechanism and Energetics of Secondary Oxidation Reactions in the Aerobic Oxidation of Hydrocarbons Catalyzed by Mn-Doped Nanoporous Aluminophosphates

Electronic structure calculations employing hybrid exchange DFT methods under periodic boundary conditions are applied to unravel the mechanism and energetics of the secondary oxidation reactions of hydrocarbons catalyzed by Mn-doped nanoporous aluminophosphates. Secondary oxidations are favored by the activated nature of the primary oxidative products, alcohols, which have weaker C–H bonds than the corresponding hydrocarbon molecules. Our model accounts for the secondary oxidations of terminal alcohols; a double H-abstraction from these compounds, first by MnIII complexes with radical-type oxo-based ligands, and then by framework O atoms nearest neighbor to Mn, yields aldehyde molecules or ketones if nonterminal alcohols are oxidized. These aldehydes are then transformed first into carbonyl-containing α-hydroperoxide derivatives through H-abstraction, addition of O2, and a subsequent H-transfer. These hydroperoxides can then only be decomposed by the action of MnII sites which, depending on the stereochemistry of the hydroperoxide adsorption onto the Mn sites, yield the carboxylic acid final products directly or after a new H-abstraction. The knowledge gained in our study allows us to propose a mechanism for the secondary oxidation of ketones to give carboxylic acids, a route that involves cleavage of C–C bonds adjacent to the carbonyl group and gives place to carboxylic acids of shorter chain-length than the initial hydrocarbon, products commonly found during the experimental reaction.

Thermal Degradation of Polyethylene Bags and Millet Stalks: Influence of the Temperature and the Local Concentration of Oxygen on the Conversion Rate of Carbon

This paper concerns the influence of temperature and local concentration of oxygen on the conversion efficiency of carbon into CO, CO2, CH4, C3H8, C2H4, C2H2, C2H6, C6H6, during the thermal degradation of plastic bags and millet stalks. The experimental device used is the tubular kiln, coupled to an analyzer Fourier Transform Infrared (FTIR) and a Non Dispersive Infrared analyzer (NDIR). Temperatures are considered between 800 and 1000°C. Local concentrations of oxygen during thermal degradation are 0%, 10% and 21%. On the one hand results obtained on the influence of temperature show that for each type of thermal degradation and whatever the temperature of the combustion, the rate of conversion of carbon remains substantially the same. In the case of plastic bags, the rate of carbon converted during pyrolysis is about 90% of carbon converted during reductive combustion. On the other hand, with millet stalks, the carbon converted represents only 60% of the rate of carbon converted during combustion to 10% oxygen. 1 to 2% of carbon not analyzed is in the form of aromatic compounds that are found most often in the soot and/or tar from this combustion system. Moreover, whatever the temperature, the overall efficiency of carbon conversion increases linearly with the local concentration of oxygen. During the thermal degradation of plastic bags, we see that the reducer environment has fostered the conversion of 7% of carbon more while the presence of oxygen in double proportion promotes the conversion of 27% carbon. Regarding the influence of the local content of oxygen, it is clear that for plastic bags, the reactions of oxidation of CO into CO2 tend to be favored for the benefit of those of hydrocarbons into CO. The formation of CO and CO2 by oxidation of light hydrocarbons is primarily from gaseous compounds CH4 and C2H4. At 950°C, we have also acetylene (C2H2) which is involved in the production of carbon oxides. At 1000°C, benzene (C6H6) heavily involved in the formation of CO and CO2. However, with millet stalks, more the local content of oxygen increases, more combustion is better, that is to say that the oxidation reactions producing CO2 are faster than the oxidation reactions of hydrocarbons into CO. The rate of carbon converted into CO and CO2 is higher for millet stalks than for plastic bags, due to this oxygen levels higher in millet stalks than in plastic bags. Similarly, for the millet stalks, from pyrolysis to combustion (at 10 and 21% oxygen), there is practically no hydrocarbon emitted.

Competitive no, co and hydrocarbon oxidation reactions over a diesel oxidation catalyst

AbstractThe oxidation of NO, CO and hydrocarbons (HC) individually, in mixtures, and with NO2 were investigated over a monolith‐supported Pt/Al2O3 catalyst under oxidising conditions. Although competitive adsorption and inhibition by other species on oxidation reactions is a relatively well‐known phenomenon, this study represents a more comprehensive examination of such effects between key components in vehicle exhaust gases. NO2 was completely reduced by CO and C3H6, under NO2 limited conditions, at temperatures as low as 110°C and at temperatures above 140°C with dodecane and m‐xylene. NO2 was then again observed once the extent of oxidation of the other species by oxygen was significant. Under the conditions tested, NO, CO and HC oxidation was inhibited by NO2 in the feed gas mixture. HC were also found to inhibit the oxidation of NO and other HC species due to site adsorption competition. For CO, HC did not change the onset of oxidation, but did inhibit the extent after their light off began. At low temperatures, CO was initially found to inhibit NO oxidation, but at higher temperatures, once CO oxidation was significant, CO promoted NO conversion to NO2. The observed inhibition effects of the different gases on HC oxidation were not additive, indicating one species would cause inhibition, but once its inhibition ended, another species could still then cause inhibition. The combined effect of C3H6, NO and NO2 on CO conversion was found to be additive. This is because CO oxidation started prior C3H6. © 2011 Canadian Society for Chemical Engineering

ChemInform Abstract: Preparation and Reactivity of Polystyrene‐Supported Iodosylbenzene: Convenient Recyclable Oxidizing Reagent and Catalyst.

AbstractThe title compound is used in oxidation reactions of alcohols and aromatic hydrocarbons.

Mechanism and Site Requirements of Thiophene Hydrodesulfurization Catalyzed by Supported Pt Clusters

AbstractKinetic, isotopic, and chemical analysis methods are used to examine the identity and kinetic relevance of elementary steps and the effects of Pt cluster size on thiophene hydrodesulfurization (HDS) turnover rates. Quasi‐equilibrated H2 and H2S heterolytic dissociation steps lead to sulfur chemical potentials given by the prevalent H2S/H2 ratio and to cluster surfaces with a metallic bulk, but near‐saturation sulfur coverages, during steady‐state catalysis. Sulfur‐vacancies on such surfaces are required for η1(S) or η4 thiophene adsorption modes and for H2 and H2S dissociation steps. H‐assisted CS bond cleavage of η1(S) thiophene and H‐addition to η4 thiophene limits rates of direct desulfurization and hydrogenation sulfur removal pathways, respectively. These steps, their kinetic relevance, and the prevalent sulfur‐saturated surfaces resemble those on Ru clusters; they are also consistent with the observed kinetic effects of reactants and products on rates, with the rapid isotopic exchange in H2/D2/H2S mixtures during HDS catalysis, and with measured H2/D2 kinetic isotope effects. Small Pt clusters exhibit lower turnover rates, stronger inhibition by H2S, and a greater preference for desulfurization pathways than those of large clusters. These effects reflect the prevalence of coordinatively unsaturated corner and edge sites on small clusters, which bind sulfur atoms more strongly and lead to lower densities of vacancies and to a preference for η1(S)‐bound thiophene species. Sulfur binding energies and their concomitant effects on the number of available vacancies also account for the higher turnover rates measured on Pt clusters compared with Ru clusters of similar size. These data and their mechanistic interpretation suggest that the concepts and steps proposed here apply generally to hydrogenation and direct desulfurization of organosulfur compounds. Taken together with similar observed effects of oxygen binding strength, metal identity, and cluster size for oxidation reactions of NO, hydrocarbons, and oxygenates, which also require vacancies in their respective kinetically relevant steps, these data also indicate that low reactivity of small clusters may reflect in most instances their coordinative unsaturation and the concomitant kinetic and thermodynamic preference for low vacancy concentrations on nearly saturated surfaces.

Synthesis of mesoporous Fe-incorporated alumina particles with regular pores

The incorporation of iron species content up to 20at.% in the framework of alumina containing silica has been successfully synthesized by using citric acid and an ultrasonic spray method under high acidic condition. In general, it is difficult to introduce the Fe ions into the mesopore-framework directly because of a fast dimerization rate of Fe ions. Moreover, the mesoporous alumina particle incorporating iron up to 20 at.% has not been reported yet. In this work, the pore structure of the prepared samples is hexagonal with regular pores and no agglomeration of iron oxide particles shows in the samples. This material can be a potential catalyst for selective reduction, hydrocarbon oxidation and redox reaction at high temperature.