Showing papers in "Kinetics and Catalysis in 2009"

In Situ XRD Study of Nanocrystalline Cobalt Oxide Reduction

Abstract: The reduction of nanocrystalline cobalt oxide samples (single-phase and supported on γ-Al2O3) was studied using in situ X-ray diffraction (XRD) analysis. The atomic structures of single-phase and supported Co3O4 samples were refined, and the occurrence of cationic vacancies was demonstrated. A set of methods (XRD, temperature-programmed reduction, and differential dissolution) was used to find that the reduction of supported and unsupported model cobalt oxide was considerably different. The single-phase sample was reduced in undiluted hydrogen to cobalt metal with a hexagonal closely packed structure. The reduction of the supported sample (unlike the single-phase sample) occurred through the formation of a crystalline CoO phase to the formation of cobalt metal with a face-centered cubic structure. Interaction of cobalt oxide with the γ-Al2O3 support, which hinders the reduction to cobalt metal, was detected.

Physicochemical and catalytic properties of systems based on CeO2

Abstract: The effect of synthesis conditions, the nature of components, and the ratio between the components on the phase composition, the texture, and the redox and catalytic properties of the Ce-Zr-O, Ce-Zr-M1-O (M1 = Mn, Ni, Cu, Y, La, Pr, or Nd), N/Ce-Zr-O (N = Rh, Pd, or Pt), and Pd/Ce-Zr-M2-O/Al2O3 (M2 = Mg, Ca, Sr, Ba, Y, La, Pr, Nd, or Sm) was considered. A cubic solid solution with the fluorite structure was formed on the introduction of <50 mol % zirconium into CeO2, and the stability of this solid solution depended on preparation procedure and treatment conditions. The presence of transition or rare earth elements in certain concentrations extended the range of compositions with the retained fluorite structure. The texture of the Ce-Zr-O system mainly depended on treatment temperature. An increase in this temperature resulted in a decrease in the specific surface area of the samples. The total pore volume varied over the range of 0.2–0.3 cm3/g and depended on the Ce/Zr ratio. The presence of transition or rare earth elements either increased the specific surface area of the system or made it more stable to thermal treatment. The introduction of the isovalent cation Zr4+ into CeO2 increased the number of lattice defects both on the surface and in the bulk to increase the mobility of oxygen and facilitate its diffusion in the Ce1 − x Zr x O2 lattice. The catalytic properties of the Ce-Zr-M1-O or N/Ce-Zr-M2-O systems were due to the presence of anion vacancies and the easy transitions Ce4+ ai Ce3+, M 1 2+ ai M 1 + , and N δ+ → N 0 in the case of noble metals.

Platinum nanoparticle size effect on specific catalytic activity in n-alkane deep oxidation: Dependence on the chain length of the paraffin

Abstract: The specific activity of 0.8% Pt/Al2O3 catalysts in the deep oxidation of C1–C6n-alkanes increases with an increase in the Pt particle size from 1 to 3–4 nm. Further coarsening of the particles insignificantly changes the specific activity. The size effect was studied for a series of catalysts containing platinum nanoparticles 1 to 11 nm in diameter. The specific catalytic activity variation range depends on the size of the reacting hydrocarbon molecules. As the platinum particle size increases, the specific catalytic activity increases 3–4 times for the oxidation of CH4 and C2H6 and by a factor of 20–30 for the oxidation of n-C4H10 and n-C6H14.

Metalasiloxanes: New structure formation methods and catalytic properties

Abstract: This article is a review of present-day methods of the formation of the structure of various metalasiloxanes (MS’s). Methods of designing the structure of catalytically active MS’s are discussed. In the description of synthetic methods and catalytic properties, the MS’s are divided into two groups, namely, individual and oligomeric MS’s. The first section of the review is devoted to MS’s with coordinatively unsaturated metal sites and to cagelike MS’s. The methods of formation of MS-based catalytic surfaces are analyzed, and synthetic methods converting these surfaces into ordered inorganic catalytic systems are discussed. The second section of the review presents the methods of synthesis of MS oligomers, the ways of regulating the structure of these compounds, and the use of the MS’s as the basic component of catalytic systems for petrochemical syntheses and halohydrocarbon conversion.

Mechanism and kinetics of the thermal decomposition of 5-aminotetrazole

Abstract: The kinetics of 5-aminotetrazole thermal decomposition in the condensed phase at high heating rates (∼100 K/s) was studied by the dynamic mass spectrometric thermal analysis using a molecular beam sampling system, and the product composition was determined. Two routes of 5-aminotetrazole decomposition were distinguished, one yielding HN3 and NH2CN (route 1), and the other N2 and CH3N3 (route 2). The activation energy and rate constant of 5-AT decomposition were determined for each route.

Radical cations of aromatic molecules with high ionization potentials on the surfaces of oxide catalysts: Formation, properties, and reactivity

Abstract: The results obtained by the authors on the formation and properties of the radical cations of benzene and other molecules with high ionization potentials on the surfaces of ZSM-5 zeolites and sulfated zirconium dioxide are analyzed in this paper. It was found that radical cations of aromatic compounds can be obtained both by a thermal process and under illumination with visible light. Radical cations were found to be key intermediates in the low-temperature polycondensation of aromatic compounds on these catalysts. A possible mechanism of the formation of radical cations and the nature of the sites responsible for these processes are discussed.

The effect of spinel type support FeAlO3, ZnAl2O4, CrAl3O6 on physicochemical properties of Cu, Ag, Au, Ru supported catalysts for methanol synthesis

Abstract: The comparative study of the role of binary oxide support on catalyst physico-chemical properties and performance in methanol synthesis were undertaken and the spinel like type structures (ZnAl2O4, FeAlO3, CrAl3O6) were prepared and used as the supports for 5% metal (Cu, Ag, Au, Ru) dispersed catalysts. The monometallic 5% Cu/support and bimetallic 1% Au (or 1% Ru)-5% Cu/support (Al2O3, ZnAl2O4, FeAlO3, CrAl3O6) catalysts were investigated by BET, XRD and TPR methods. Activity tests in methanol synthesis of CO and CO2 mixture hydrogenation were carried out. The order of Cu/support catalysts activity in methanol synthesis: CrAl3O{ia6} > FeAlO3 > ZnAl2O4 is conditioned by their reducibility in hydrogen at low temperature. Gold appeared more efficient than ruthenium in promotion of Cu/support catalysts.

Nonoxidative conversion of methane into aromatic hydrocarbons on Ni-Mo/ZSM-5 catalysts

Abstract: The nonoxidative conversion of methane into aromatic hydrocarbons on high-silica zeolites ZSM-5 containing nanosized powders of molybdenum (4.0 wt %) and nickel (0.1–2.0 wt %) was studied. Data on the acid characteristics of the catalysts and the nature and amount of coke deposits formed on the surface of the catalysts were obtained using the thermal desorption of ammonia and thermal analysis. The microstructure and composition of Ni-Mo/ZSM-5 catalysts were studied by high-resolution transmission electron microscopy and energy-dispersive X-ray analysis. The formation of various chemical species in the samples was detected: oxide-like clusters of Mo within zeolite channels (∼1 nm), molybdenum carbide particles (5–30 nm) on the outer surface of the zeolite, and Ni-Mo alloy particles with different compositions (under reaction conditions, carbon filaments grew on these particles). It was found that, as the Ni content was increased from 0.1 to 2.0 wt %, the rate of deactivation of the catalytic system increased because of blocking pores in the zeolite structure by filamentous carbon up to the formation of condensed coke deposits.

Catalytic condensation of glycolaldehyde and glyceraldehyde with formaldehyde in neutral and weakly alkaline aqueous media: Kinetics and mechanism

Abstract: The kinetics of glycolaldehyde and glyceraldehyde condensation with formaldehyde in a neutral aqueous medium in the presence of homogeneous phosphates and in a weakly alkaline medium in the presence of MgO was studied. The temperature dependences of the observed kinetic constants and the apparent activation energies of the reactions were determined. A reaction scheme for the interaction of lower monosaccharides with formaldehyde was derived from analyses of the reaction products.

New high-selectivity hydrogenation catalysts prepared from bimetallic acetate complexes

Abstract: The catalytic properties of new Pd-Zn/Al2O3 catalysts in selective acetylene hydrogenation in an acetylene-ethylene mixture at 30–120°C and atmospheric pressure are reported. The catalysts prepared from the bimetallic complex Pd-Zn(OOCMe)4(OH2) are much more selective than the catalysts prepared by simultaneously supporting the homonuclear complexes Pd3(OOCMe)6 and Zn(OOCMe)2 · 2H2O. It is demonstrated by diffuse reflectance IR spectroscopy of adsorbed CO that the heat treatment of the supported bimetallic complex at 250°C in flowing H2 yields a Pd-Zn alloy on the surface. It is this alloy that ensures the high selectivity of the Pd-Zn/Al2O3 catalysts.

Properties of surface compounds in methanol conversion on γ-Al2O3: Data of in situ IR spectroscopy

Abstract: In situ IR spectroscopic studies show that a formate, an aldehyde-like complex, and bridging and linear methoxy groups exist on the alumina surface involved in methanol conversion. In the absence of methanol in the gas phase, the interaction between two bridging methoxy groups yields dimethyl ether in the gas phase. When methanol is present in the gas phase, it interacts with methoxy groups on the surface. This reaction makes the main contribution to the formation of dimethyl ether. The linear methoxy group undergoes conversion via several routes. The main route is desorption with methanol formation in the gas phase, and no more than 10% of the linear methoxy groups are converted into formate and aldehyde, which are CO2 sources in the gas phase. In the absence of methanol in the gas phase, the conversion rate of the methoxy groups is independent of the presence of water and oxygen. A scheme of the surface reactions is suggested to explain the conversion of the methoxy groups.

“Salt in a porous matrix” adsorbents: Design of the phase composition and sorption properties

Abstract: This review formulates the concept of target-oriented synthesis of two-component “salt in a porous matrix” (SPM) adsorbents designed for processes such as gas dewatering, moisture control, heat conversion in adsorption heat pumps, and equilibrium shifting in catalytic reactions. In terms of this approach, the requirements imposed on an ideal adsorbent, which is optimal for a particular application, are initially formulated; then, a material with nearly optimal properties is synthesized. Methods for the target-oriented synthesis of SPM adsorbents with the required properties are considered. The effects of the nature of the salt and the matrix, the salt content, the pore size of the matrix, and the synthesis conditions on the phase composition and adsorption properties of the SPM adsorbents are studied.

Kinetics and mechanism of chemical reactions in the H2/O2/N2 flame at atmospheric pressure

Abstract: The kinetics and mechanism of chemical reactions in the H2/O2/N2 flame were studied experimentally and by simulating the structure of premixed laminar flat atmospheric H2/O2/N2 flames of different initial compositions. The concentration profiles for stable compounds (H2, O2, and H2O), H atoms, and OH• radicals in flames were measured by molecular-beam sampling mass spectrometry using soft electron-impact ionization. The experimental data thus obtained are in good agreement with the results of simulations in terms of three familiar kinetic mechanisms, suggesting that these mechanisms are applicable to the description of the flame structure in hydrogen-oxygen mixtures at atmospheric pressure.

Removal of dibenzothiophene in diesel oil by oxidation over a promoted activated carbon catalyst

Abstract: Oxidative removal of dibenzothiophene (DBT) in n-octane solution by H2O2 on a promoted activated carbon (AC) catalyst was studied. DBT adsorption and catalytic behaviors on AC were examined. Effects of pH in aqueous phase, amounts of AC and formic acid (HCOOH) for promotion as well as initial molar H2O2/S ratio were investigated. Experimental results led to conclusion that DBT was readily oxidized by H2O2 over an AC catalyst promoted by HCOOH. Suitable amount of AC can improve the activity of H2O2 resulting in a deeper extent of sulfur removal. A 100% conversion of DBT in an octane solution by H2O2 oxidation was attained on the HCOOH-H2O2/AC catalyst at 80°C for a reaction time of 30 min.

Effect of silicon dioxide on the formation of the phase composition and pore structure of titanium dioxide with the anatase structure

Abstract: The formation of the structure of titanium dioxide modified with silicon dioxide, which was introduced as tetraethyl orthosilicate, was studied. It was found that the formation of the nanocrystalline structure of TiO2 occurred upon the modification of titanium dioxide with silicon dioxide. This nanocrystalline structure of TiO2 was formed by highly dispersed anatase particles of size 6–10 nm stabilized by silicon oxide layers, which were formed upon the decomposition of tetraethyl orthosilicate. An increase in the modifier concentration resulted in a deceleration of the growth of anatase particles and an increase in the temperature of the phase transition of anatase to rutile. It was found that the anatase phase in the samples containing 5–15 wt % SiO2 was stable up to 1000°C. The stabilization of highly dispersed anatase particles facilitated the retention of the developed fine-pore structure of xerogels with a pore diameter of 4 nm up to 900°C.

Unexpected participation of nucleophiles in the reaction of palladium(II) acetate with divalent 3d metals

Abstract: The kinetics of reactions of palladium(II) acetate with cobalt(II), nickel(II), and copper(II) acetates were studied by spectrophotometry. These reactions produce heterobimetallic complexes PdII(μ-OOCMe)4MII(OH2)(HOOCMe)2, where M = Co, Ni, or Cu. These reactions are very slow in carefully dehydrated (<0.01% H2O) acetic acid, but are considerably enhanced by water or acetonitrile. Our data indicate that the activation of the kinetically inert ring structure of the initial palladium complex Pd3(μ-OOCMe)6 by means of the nucleophilic attack of an H2O or acetonitrile molecule is the key step of the reaction mechanism.

Laser-induced luminescence associated with surface hydroxide groups in Al2O3

Abstract: Laser-induced luminescence of OHs groups for undoped Al2O3 oxides of various phase compositions was excited by pulsed nitrogen laser radiation at 337.1 nm. The luminescence band at 500–650 nm assigned to hydroxide groups of Al2O3, actually, consists of several lines at 500–515, 553, 567, 577, 607, and 633 nm; these constituent bands can be assigned to various types of OHs surface groups. In the low-temperature phases of the γ→δ→θ-Al2O3 series, excitation at a wavelength of 337.1 nm gave rise to a characteristic luminescence band associated with surface hydroxide groups of Al2O3 that appeared at 770 nm.

Effective and recoverable homogeneous catalysts for the transesterification of dimethyl carbonate with ethanol: Lanthanide triflates

Abstract: The catalytic activities of metal triflates were tested for the transesterification of dimethyl carbonate (DMC) with ethanol. It was found that yttrium triflate was the most efficient homogeneous catalyst. When the transesterification reaction was catalyzed by yttrium triflate at 76–80°C, 7 h, ethanol to DMC in 6: 1 molar ratio, 0.35 mol % of catalyst based on DMC, the conversion of DMC was 89.2%, the selectivities of diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) were 85.1 and 13.6%, respectively. Yttrium triflate was reused 5 times for the transesterification without loss of its catalytic activity.

Kinetics and mechanism of oxidation of L-Alanine by N-bromophthalimide in the presence of sodium dodecyl sulfate

Abstract: The kinetics of oxidation of L-Alanine (Ala) by N-bromophthalimide (NBP) was studied in the presence of an anionic surfactant, sodium dodecyl sulfate, in acidic medium at 308 K. The rate of reaction was found to have first-order dependence on [NBP], fractional order dependence on [Ala] and inverse fractional order dependence on [H+]. The addition of reduced product of the oxidant [Phthalimide] has decreased the rate of reaction. The rate of reaction increased with increase in inorganic salts concentration i.e., [Cl−] and [Br−], whereas a change in ionic strength of the medium and [Hg(OAc)2] had no effect on oxidation velocity. The rate of reaction decreased with a decrease in dielectric constant of the medium. CH3CN was identified as the main oxidation product of the reaction. The various activation parameters have been computed and suitable mechanism consistent with the experimental findings has also been proposed. The micelle-binding constant has been calculated.

Structural and functional design of catalytic converters for emissions from internal combustion engines

Abstract: We consider some features of technology for manufacturing advanced three-way (CO/NOx/CnHm) catalytic converters for emissions of internal combustion engines, namely, application, stabilization, and modification of γ-Al2O3 second supports on synthetic cordierite matrices and Pt, Pd, and Rh active components, as well as oxidation of finely divided carbon on the surface of soot filters coated with a catalyst coating in the form of binary oxide compositions (CuCr2O4 and CuCo2O4) using a number of oxidizers (O2, O3, NO, NO2, H2O, and CO2).

Reactions of arylnitroso oxides with substituted styrenes: Kinetics and products

Abstract: The kinetics of the reactions of phenylnitroso oxide and 4-CH3O- and 4-Cl-phenylnitroso oxides with a series of substituted styrenes (4-X-C6H4-CH=CH2; X = H, CH3O, Cl, CN) in acetonitrile at 22 ± 2°C was studied using the flash photolysis technique. It was shown for 4-CH3O-C6H4NOO as an example that only the trans isomers of the nitroso oxides are involved in the reaction. There is a linear correlation between the logarithm of the rate constant and the electronic properties of the substituent in the nitroso oxide aromatic ring on the Hammett scale: ρ = 2.3 ± 0.3 (r = 0.993) for 4-CH3O-styrene ρ = 2.03 ± 0.07 (r = 0.995) for styrene, and ρ = 1.77 ± 0.05 (r = 0.9996) for 4-Cl-styrene. Both the electron-donating and electron-withdrawing substituents in the aromatic ring of styrene increase its reactivity toward a given nitroso oxide. An analysis of the products of phenyl azide photooxidation in the presence of styrene showed that the product of phenylnitroso oxide [3+2]cycloaddition to the double bond of the olefin decomposes into benzalaniline and carbonyl oxide.

Vibrational nonequilibrium of the HO2 radical in the reaction between hydrogen and oxygen at 1000 < T < 1200 K

Abstract: A theoretical model of the chemical and vibrational kinetics of high-temperature hydrogen oxidation is presented. The central feature of this model is that it consistently takes into account the vibrational nonequilibrium of the HO2 radical as the most important intermediate. The basic distinction between the model and the conventional kinetic schemes is that the former does not consider the reaction H + O2 → O + OH as an elementary event. Calculated data are presented for 1000 < T < 1200 K and 0.9 < P < 2.0 atm, the conditions typical of shock tube experiments. The calculated data show that the nonequilibrium character of the process is the cause of the observed dependence of the “effective rate constant” of the overal reaction H + O2 → O + OH on experimental conditions. It is demonstrated that this approach is promising from the standpoint of reconciling the predictions of the theoretical model with experimental data obtained by different authors for various compositions and conditions using different methods.

Reduction of nitrogen oxides in diesel exhaust: Prospects for use of synthesis gas

Abstract: Already commercialized and some of the most promising technologies of nitrogen oxide reduction in automotive diesel exhaust are compared. The Boreskov Institute of Catalysis (Siberian Branch, Russian Academy of Sciences) is developing an advanced method for the selective catalytic reduction of NO x with synthesis gas produced on board by the catalytic conversion of diesel fuel. The activity of the Ag/Al2O3 catalytic system in NO x reduction by H2 + CO admixtures is studied for both a model composition of the exhaust gas and under real diesel operation conditions.

Kinetics and mechanism of catalytic acetylene hydrochlorination with gaseous HCl on the surface of mechanically activated K2PdCl4

Abstract: The catalyst for acetylene hydrochlorination with gaseous HCl at room temperature is prepared by mechanical pretreatment of K2PdCl4 in an acetylene atmosphere. The rate-determining step of the reaction is the chloropalladation of π-coordinated acetylene involving an HCl molecule. As a consequence, the replacement of HCl with DCl brings about a kinetic isotope effect of 2.8 ± 0.4, which differs substantially from that observed in the protodemetalation of the intermediate palladium(II) chlorovinyl derivative yielding vinyl chloride (6.8 ± 0.6).

Spectroscopic study of the properties of surface compounds in methanol conversions on Cu/γ-Al2O3

Abstract: The reactions of methanol on the (10% Cu)/γ-Al2O3 surface were studied by the spectrokinetic method (simultaneous measurements of the conversion rates of surface compounds and the product formation rates). Bridging and linear methoxy groups result from the interaction of methanol with surface hydroxyl groups. Formate and aldehyde-like complexes form by the oxidative conversion of the linear methoxy groups. Hydrogen forms via the recombination of hydrogen atoms on copper clusters, and the hydrogen atoms result from interconversions of surface compounds. The source of CO2 in the gas phase is the formate complex, and the source of CO is the aldehyde complex. In the absence of methanol in the gas phase, dimethyl ether forms by the interaction between two bridging methoxy groups. When present in the gas phase, methanol reacts with methoxy groups on the surface. The roles of oxygen and water vapor in the conversions of surface compounds are discussed.

Reactivity of Arylnitroso Oxides to Triphenylphosphine

Abstract: The kinetics of reactions between phenylnitroso oxide, 4-CH3O-, 4-CH3-, or 4-Br-phenylnitroso oxide and triphenylphosphine in acetonitrile at 295 ± 2 K were studied using pulsed photolysis. Only trans-nitroso oxides enter this reaction. The rate constants of the reaction increase with increasing electron-acceptor properties of the substituent in the aromatic ring of nitroso oxide; they are on the order of 105 to 106 l mol−1 s−1. The extinction coefficient for trans-4-methylphenylnitroso oxide at 420 nm was estimated at 3.9 × 103 l mol−1 cm−1.

Kinetics of the Oxidation of N-Aminopiperidine with Chloramine

Abstract: The kinetics of the oxidation of N-aminopiperidine with chloramine was studied at different temperatures, with variable concentrations of the two reactants and at a pH ranging between 12 and 13.5. The reaction showed to be involving two steps: the first corresponded to the formation of a diazene intermediate, the second to the evolution of this intermediate into numerous compounds within a complex reactional chain. The rate law of the first step was determined by the Ostwald method and found to be first order with respect to each reactant. The rate constant was determined at pH 12.89 and T = 255°C: k2 = 1.15 × 105 exp(−39/RT) l mol−1 s−1 (E2 in kJ/mol). With decreasing pH value, the first exhibited acid catalysis phenomena, and diazene was converted into azopiperidine particularly faster. This created overlapping UV-absorptions between chloramine and azopiperidine, also observed in HPLC. GC/MS analyses were used to identify some of the numerous by-products formed. Their proportions are dependent of both pH and the reactants’ concentrations ratio. A reaction mechanism taking this relationship into account was suggested.

Regulating the Physicochemical and Catalytic Properties of Layered Aluminosilicates

Abstract: Basic methods of the introduction of metal ions into the interlayer space of natural layered aluminosilicate (LAS) are considered. The physicochemical and structural properties of pillared LAS’s depend on the nature of the cation, as well as on the cation intercalation method and conditions. The catalytic properties and stability of an LAS in acid-catalyzed and oxidation reactions may depend on its textural and physicochemical properties.

Henry and Knoevenagel reactions catalyzed by methoxyl propylamine acetate ionic liquid

Abstract: Henry reactions and Knoevenagel reactions, used to prepare substituted olefins, have been limited by complex catalyst separation. In this article, methoxyl propylamine acetate ionic liquid was used as an environmentally benign catalyst for these reactions under solvent-free condition for the first time. This ionic liquid was shown to effectively catalyze Henry reactions and Knoevenagel reaction of active nitromethane compounds with various aldehydes. Yields from the catalyzed reactions were over 99% under solvent free condition. The process is highly effective, environmentally benign, and very selective. Furthermore, methoxyl propylamine acetate ionic liquid was conveniently separated with the products and easily recycled to catalyze Knoevenagel reaction again with excellent yields.

Nickel-copper-chromium catalyst for selective methane oxidation to synthesis gas at short residence times

Abstract: Data on the selective oxidation of methane to synthesis gas on a 9% NiCuCr/2% Ce/(ϑ + α)-Al2O3 catalyst in dilute mixtures with Ar at short residence times (2–3 ms) are presented. The composition, structure, morphology, and adsorption properties of the catalyst with respect to oxygen and hydrogen before and after reaction were studied using XRD, BET, electron microscopy with electron microdiffraction, TPR, TPO, and TPD of oxygen and hydrogen. The following optimum conditions for the preparation and pretreatment of the catalyst for selective methane reduction were found: the incipient wetness impregnation of a support with aqueous nitrate solutions; drying; and heating in air at 873 and then at 1173 K (for 1 h at either temperature) followed by reduction with an H2-Ar mixture at 1173 K for 1 h. At a residence time of 2–3 ms (space velocity to 1.5 × 106 h−1) and 1073–1173 K, the resulting catalyst afforded an 80–100% CH4 conversion in mixtures with O2 (CH4/O2 = 2: 1) diluted with argon (97.2–98.0%) to synthesis gas with H2/CO = 2: 1. The selectivity of CO and H2 formation was 99.6–100 and 99–100%, respectively; CO2 was almost absent from the reaction products. The catalyst activity did not decrease for 56 h; carbon deposition was not observed. A possible mechanism of the direct oxidation of CH4 to synthesis gas is considered.