Structural and mechanistic insights into methane oxidation by particulate methane monooxygenase

Particulate methane monooxygense (pMMO) is an integral membrane copper-containing enzyme that converts methane to methanol. Knowledge of how pMMO selectively oxidizes methane under ambient conditions could impact the development of new catalysts. The crystal structure of Methylococcus capsulatus (Bath) pMMO reveals the composition and location of three metal centers. Spectroscopic data provide insight into the coordination environments and oxidation states of these metal centers. These results, combined with computational studies and comparisons to relevant systems, are discussed in the context of identifying the most likely site for O 2 activation.     

Controlled oxidation of methane doped catalysts irradiated by microwaves

The oxidative coupling of methane has been studied on a (SmLiO₂)_0.8(CaOMgO)_0.2 catalyst by using two different modes of heating: a conventional oven and a microwave irradiation set-up. The C₂ selectivity obtained with microwave heating was much higher than with conventional heating especially at low conversions. This difference could arise from the reduction of oxidation products (ethane, ethylene) in the gas phase under microwave irradiation.     

Mathematical modeling of the partial oxidation of hydrocarbons in a multiple-shelf reactor for the case of methylacrolein synthesis

A numerical study of the mathematical model of a multiple-shelf reactor in which the fixed beds of a porous catalyst alternate with built-in heat exchangers is performed. The possibility of carrying out the process of methylacrolein production by the partial oxidation of isobutylene by air oxygen is shown and the optimum conditions are determined.     

Modification of a mercury-catalyzed system for the oxidation of methane to methanol

The novel mercury-catalyzed system for the oxidation of methane to methanol was studied in both supercritical and non-supercritical reaction conditions. Systematic experimental design was applied to study the effect of temperature, pressure and mole ratio. Reaction conditions were selected by using three-level fractional factorial design. The runs were performed in a high-pressure autoclave. Temperature had the strongest effect on the methanol yield. The mole ratio had no clear effect in the studied region. Surprisingly, the role of pressure was not significant. However, the supercritical conditions seem to have some effect on the methanol yield.     

甲烷部分氧化过程的热力学

对杂多酸与醋酸混合溶剂体系,碘为催化剂的甲烷液相部分酯化过程进行了热力学计算。在298.15—1 000 K温度下,分别计算了甲烷部分氧化反应可能存在的4条反应途径的反应焓变,吉布斯自由能变及平衡常数。结果表明,甲烷液相部分氧化反应中,经由甲烷与碘生成中间物碘甲烷,碘甲烷再与醋酸酯化合成醋酸甲酯的过程是可以实现的,为提高甲烷转化率需改进控制步骤甲烷与碘生成碘甲烷的反应速率。     

Optimum washcoat thickness of a monolith reactor for syngas production by partial oxidation of methane

In this paper, syngas (hydrogen and carbon monoxide) production was investigated by a numerical model of an adiabatic monolithic reformer (e.g. for a micro fuel cell system). The study includes the thermal and diffusive properties of a washcoat of finite thickness that is modeled as a porous layer composed of a ceramic support containing catalytic active rhodium sites. It was combined with a two-dimensional radially symmetric model of a single tubular mini-channel, considering both the thermal and the diffusive transport phenomena in all domains. It was found that both the methane conversion and the hydrogen yield depended markedly on the washcoat thickness. An interesting result was obtained by implementing the common experimental conditions into the numerical model: if the inlet volume flow and the amount of catalyst per washcoat volume are constant, an optimum washcoat thickness of was found, where the hydrogen yield is maximal. For a thinner washcoat, the smaller amount of catalyst is limiting, leading to a low methane conversion. For a thicker washcoat, the limiting effect is the reduced residence time, which stems inherently from the constraint of constant volume flow, rather than the increased diffusive resistance.The demonstration of the existence of an optimum washcoat thickness is important, because it can have economic effects due to saving of the precious catalyst rhodium.     

Characterization of a nickel-strontium phosphate catalyst for partial oxidation of methane

A nickel-strontium phosphate catalyst was recently reported to exhibit high activity and selectivity in partial oxidation of methane (POM). Further characterizations have been performed in the present work in order to better understand the characteristics of this catalyst. TEM showed that very fine nickel particles of a few nanometers of the size were present in the needle shape in the sample after the reaction. TPR showed the presence of three nickel species, confirming that the nickel in the strontium hydroxyapatite and phosphate structures comes out as fine particles and is reduced during the reaction. As the calcination time during the preparation increased, the total re-oxidation temperature became higher. This is considered due to larger crystallite size owing to the longer calcination, which results in a smaller amount of nickel coming out of the matrix to the surface.     

Improving selectivity during methane partial oxidation by use of a membrane reactor

A reactant-swept catalytic membrane reactor for partial oxidation of methane to formaldehyde has been modeled. Kinetic parameters were taken from the literature for a V₂O₅/Sio₂ methane partial oxidation catalyst, and membrane parameters characteristic of commercially available materials were used. The models show that the selectivity for formaldehyde can be significantly improved by using a membrane reactor.     

Novel supports for nickel-based catalysts for the partial oxidation of methane

Zirconia-supported nickel catalysts with different amounts of aluminum (Al/Zr = 0.2, 1 and 2) were studied in this work in order to find alternative supports for nickel-based catalysts for the partial oxidation of methane. This reaction is a promising route for producing hydrogen and syngas for different applications. Samples were prepared by precipitation and impregnation techniques, characterized by several techniques and evaluated in the partial oxidation of methane in the range of 450–750 °C and 1 atm. It was found that aluminum affects the textural and catalytic properties of zirconia-supported nickel catalysts. The tetragonal phase of zirconia was stabilized by aluminum and gamma-alumina was also found in the aluminum-richest samples. Aluminum increased the porosity and the specific surface area of the solids. The catalytic activity also increased with the amount of aluminum in solids probably due to the stronger interaction of nickel with the support, which slowly generates active sites during the reduction step. The methane conversion and hydrogen selectivity increased with temperature, indicating no deactivation. The hydrogen to carbon monoxide molar ratio decreased due to aluminum but was not significantly affected by temperature. The coke produced was not harmful to the catalysts and aluminum affected its amount, although no simple relationship was found between these parameters. The most promising catalyst was the sample with aluminum to zirconium molar ratio of 2, which showed high activity and hydrogen selectivity and was stable under the reaction condition.     

Novel glass crystal catalysts for the processes of methane oxidation

Novel catalysts were prepared from magnetic microspheres and cenospheres recovered from fuel ashes being formed in combustion of Irsha-Borodinskii lignite and Kuznetskii coal. The specific features of microsphere formation in the coal combustion were discussed. The morphology as well as composition of different magnetic microspheres and cenospheres were studied by SEM, electron probe microanalysis and Mössbauer spectroscopy. The morphology of globules, crystallite size and defect structure of active phase was established to depend on the basicity of the glass phase. It was shown that catalytic activity of magnetic microspheres and cenospheres in the reaction of deep oxidation of methane is determined by the spinel phase and depends on the extent of its accessibility and type of defect structure.     

国内外甲烷催化部分氧化技术进展

介绍了国内外甲烷催化部分氧化制合成气技术的研究进展。主要工艺包括固定床工艺、流化床工艺和陶瓷膜工艺。此外，在反应器方面，还对两项最新专利技术进行了讨论。最后，提出了甲烷催化部分氧化制合成气技术的发展趋势，为我国在天然气利用方面的技术开发提供了参考和依据。     

Empirical model for methane oxidation using a composted pine bark biofilter

Methane concentration in the explosive range is of particular concern in the confined space of underground mining environments, where the hazards of accidental ignition of methane may be further compounded by coal dust explosions. The aim of this study was to determine whether composted pine bark, could be used as biofiltration support media for methane oxidation and to determine the degradation rates of methane concentrations approaching the explosive range (i.e. 5.5% v/v methane). Although of organic origin, composted pine bark is mainly composed of non-labile and recalcitrant large molecular weight molecules due to the fact that the labile organic compounds in the bark are oxidised during the composting process. Methane removal efficiencies in a composted pine bark biofilter were determined at methane concentrations ranging from 0.1 to 2.5% (v/v) and retention times of 20-400 min. Methane removal efficiencies exceeding 70% were obtained when the biofilter was subjected to gas retention times in excess of 30 min and methane concentrations up to 0.5% (v/v). The data obtained were used to develop an empirical model that successfully described the overall removal efficiency with an R² value of 0.97. It was concluded that composted pine bark could indeed be successfully utilised in passive gas-flow biofiltration for the attenuation of methane in worked underground coal mining chambers.     

Methanol formation at high pressure by the catalyzed oxidation of natural gas and by the sensitized oxidation of methane

A three part study of the partial oxidation of natural gas or methane to methanol was carried out. In the first part, the effect of reactor wall composition on the homogeneous oxidation of natural gas was determined at a pressure of 30 atm (1 atm=1.01325·10⁵ Pa) and temperatures of 350–400°C. In the second part, the effect of solid catalysts on the oxidation of natural gas was determined in a heterogeneous system at 30 atm and various temperatures. Finally, the effect of various homogeneous 'sensitizers' on the oxidation of pure methane at 10 atm was evaluated.     

Ion oxide conductor as a catalytic membrane for selective oxidation of hydrocarbons

A catalytic membrane reactor using ion‐oxide conductors as catalysts is experienced in selective oxidative dimerization of propene to C₆‐dimers. Structural and textural properties, catalytic and non‐catalytic reactivities of M‐doped Bi₂O₃ (M = La, Ce, Eu, Er, V, Nb) are studied. TGA experiments show that dopants increase the rates of reduction and reoxidation of Bi₂O₃, but that the reoxidation of the catalysts is rate limiting. During catalysis, the best yields in 1,5‐hexadiene and benzene are obtained with cerium‐doped Bi₂O₃. This revised version was published online in July 2006 with corrections to the Cover Date.     

甲烷部分氧化制乙炔过程研究

The partial oxidation of hydrocarbons is an important technical route to produce acetylene for chemical industry.The partial oxidation reactor is the key to high acetylene yields.This work is an experimental and numerical study on the use of a methane flame to produce acetylene.A lab scale partial oxidation reactor was used to produce ultra fuel-rich premixed jet flames.The axial temperature and species concentration profiles were measured for different equivalence ratios and preheating temperatures,and these were compared to numerical results from Computational Fluid Dynamics(CFD)simulations that used the Reynolds Averaged Navier-Stokes Probability Density Function(RANS-PDF)approach coupled with detailed chemical mechanisms.The Leeds 1.5,GRI 3.0 and San Diego mechanisms were used to investigate the effect of the detailed chemical mechanisms.The effects of equivalence ratio and preheating temperature on acetylene production were experimentally and numerically studied.The experimental validations indicated that the present numerical simulation provided reliable prediction on the partial oxidation of methane.Using this simulation method the optimal equivalence ratio for acetylene production was determined to be 3.6.Increasing preheating temperature improved acetylene production and shortened greatly the ignition delay time.So the increase of preheating temperature had to be limited to avoid uncontrolled ignition in the mixing chamber and the pyrolysis of methane in the preheater.     

Partial oxidation of methane in a multistage-compression chemical reactor

A theory of noncatalytic partial oxidation of methane in a superadiabatic cyclic compression chemical reactor using the operating principle of internal combustion engine is developed. It is shown that in a two-stroke reactor the conversion of methane to syngas with a H₂/CO ratio equal to 2 reaches 0.95 to 0.99 at low mixture compression ratios of 10 to 15. The energy efficiency (product-yield-to-power ratio) reaches 3 m³ of syngas per 1 kWh of power consumed.     

甲烷偶联合成碳二烃反应研究进展

甲烷直接转化为烃类是天然气合理利用的趋势和资源优化配置的要求，近年来国内外的相关研究日新月异，本文综述了甲烷偶联制碳二烃反应中的催化剂和技术。     

Quantum-chemical description of the active sites for the selective oxidation of hydrocarbons

Different aspects of quantum chemical modelling of catalytic systems are discussed. Further, the electronic structure of various V_nO_m clusters representing the vanadium pentoxide (010) surface is studied and the reactivity of different surface oxygen sites with respect to adsorption of hydrogen as well as propylene is examined. Results of ab initio HF and DFT calculations are compared with those of the semiempirical INDO-type method. It is found that the different quantum chemical methods lead to the same qualitative results. Satisfactory convergence in cluster properties is achieved for clusters of ten vanadium atoms. The saturation of dangling bonds by hydrogen atoms does not influence the properties of the oxygen centers significantly. Among different oxygen centers the oxygens bridging two bare vanadium atoms are most negatively charged. Hydrogen binds to all inequivalent oxygen sites with the strongest binding occurring for oxygens bridging two vanadium atoms. INDO cluster studies for propylene adsorption/reaction on V₂O₅ (010) show that different approaches of the molecule to the surface yield different surface complexes which can then react to form different products.