Control of the directions of oxidative transformation of methane over nickel-based catalysts by acid-base properties

Two completely different directions of the oxidative transformation of methane (OTM) were performed on nickel-based catalysts due to the different acid-base properties of those catalysts. The relatively acidic LaNiO_x and LiNiLaO_x/Al₂O₃ catalysts exhibit excellent Partial Oxidation of Methane to Syngas (POM) performance. However, the relatively basic LiNiLaO_x catalyst has a good Oxidative Coupling of Methane to C₂ Hydrocarbons (OCM) activity. The basic properties of the catalyst makes it difficult to reduce nickel and keeps it in the oxidized state. Reduced nickel is necessary for POM and oxidized nickel for the OCM reaction.     

Partial oxidation of methane and ethane to oxygenates over silica supported rhenium oxide

Silica supported rhenium oxide has been studied for partial oxidation of methane and ethane with oxygen. Loading of rhenium oxide on silica remarkably increases the conversions of methane and ethane. The presence of rhenium oxide increases the selectivity to useful oxygenates, particularly in ethane oxidation. The results suggest that rhenium oxide not only activates methane or ethane but also enhances oxygen transfer to form oxygenates. This revised version was published online in June 2006 with corrections to the Cover Date.     

Oscillations during partial oxidation of methane to synthesis gas over Ru/Al2O3 catalyst (Special column of methane transformation, Article)

Oscillations in temperatures of catalyst bed as well as concentrations of gas phase species at the exit of reactor were observed during the partial oxidation of methane to synthesis gas over Ru/Al₂O₃ in the temperature range of 600 to 850 °C. XRD, H₂-TPR and in situ Raman techniques was used to characterize the catalyst. Two types of ruthenium species, i.e. the ruthenium species weakly interacted with Al₂O₃ and that strongly interacted with the support, were identified by H₂-TPR experiment. These species are responsible for two types of oscillation profiles observed during the reaction. The oscillations were the result of these ruthenium species switching cyclically between the oxidized state and the reduced state under the reaction condition. These cyclic transformations, in turn, were the result of temperature variations caused by the varying levels of the strongly exothermic CH₄ combustion and the highly endothermic CH₄ reforming (with H₂O and CO₂) reactions (or the less exothermic direct partial oxidation of methane to CO and H₂), which were favored by the oxidized and the metallic sites, respectively. The major pathway of synthesis gas formation over the catalyst was via the combustion-reforming mechanism.     

Effect of the oxidizing capacity of ceria-based support on the conversion of methane to syngas

Ceria-based solid solutions have been proposed as catalytic supports for the conversion of methane to syngas. Control of oxygen vacancies in vacancy-rich oxides represents a promising way to stable catalysts with improved activity.     

Synthesis of Ni/Al2O3 catalysts via alkaline polyol method and hydrazine reduction method for the partial oxidation of methane

Nickel catalysts supported on γ-Al₂O₃ were synthesized in the presence of polyvinylpyrrolidone (PVP) using both alkaline polyol method and hydrazine reduction method while fixing the weight ratio of [(PVP)]/[Ni(CH₃COO)₂·4H₂O] at 2. The effects of hydrazine [N₂H₅OH]/[Ni] and [NaOH]/[Ni] molar ratios on the structural properties of the catalysts were characterized by transmission electron microscopy (HRTEM) and by X-ray diffraction (XRD). The average of monodispersed Ni nanoparticles ranged between 8.0 and 13.0 nm. The catalytic tests were performed for the partial oxidation of methane in the temperature range of 600–800 °C under a flow rate of 157,500 L kg^–1 hr^–1 with CH₄/O₂= 2. At the molar ratio of [NaOH]/[Ni] = 2, the resultant nickel nanoparticles on alumina was established completely without impurities; thus, it demonstrated the highest catalytic activity, 88% for CH₄ conversion, and H₂ selectivity, 90.60%. The optimum [N₂H₅OH]/[Ni] ratio was determined as 4.1, which means a good catalytic performance and 89.35% selectivity to H₂ for the partial oxidation of methane.     

抽放煤层气（CH4-CO2-Air）制合成气的研究——固溶体的形成对NiO/MgO催化剂性能的影响

采用浸渍法制备了NiO/MgO催化剂，用TPR、XRD、BET、H2(O2)化学吸附等技术对催化剂进行了表征，对催化剂在甲烷空气部分氧化与CO2重整耦合制合成气反应中的催化性能进行了评价。结果表明，在800 ℃焙烧的催化剂中，NiO完全与MgO形成NixMg1－xO固溶体。与低温焙烧的NiO/MgO催化剂相比，虽然NixMg1－xO固溶体催化剂的还原度较低，但可以获得较高的金属分散度和较小的金属粒径，能有效抑制积炭的生成，在反应过程中显示出良好的活性稳定性。对于900 ℃焙烧的催化剂，由于形成了更多难还原的体相固溶体，催化剂的初活性较低。     

Concerning the dependence of the selectivity of the formation of ethane and ethylene on the degree of methane conversion during its oxidative coupling

The dependences of the maximum selectivity and the limiting yield of C₂ hydrocarbons on the degree of methane conversion during its gas-phase oxidative coupling were calculated by means of kinetic simulation. The correlation between the results of the calculations and the rersults obtained in the experimental studies dealing with catalytic oxidative coupling of methane is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 568–570, March, 1995.     

The role of pressure in partial oxidation of methane

Analysis of experimental data and results of kinetic simulation throw light on the reasons for which the pressure exerts influence on the partial oxidation of methane to methanol. Among the most important factors are a crucial transition of the reaction to the steady-state chain-branched regime, an increase in the role of nonlinear gas-phase reactions, and a change in the relative contribution of heterogeneous transformations to the overall process.     

Microwave effect on partial oxidation of methane to syngas

In this paper the results of the partial oxidation of methane over Ni-based and Co-based catalysts activated by two different heating modes (conventional and microwaves) are reported. Compared with a conventional heating mode, the temperature of the catalytic bed is much lower and there is a higher selectivity of CO and H₂ with microwave irradiation.     

Self-organized nanotubular TiO2 matrix as support for dispersed Pt/Ru nanoparticles: Enhancement of the electrocatalytic oxidation of methanol

We explore oxidative electrocatalytic properties of a system consisting of bimetallic Pt/Ru nanoparticles dispersed over a nanotubular self-organized TiO₂ matrix. The nanotubular TiO₂ layers consist of individual tubes of 100 nm diameter, 500 nm length and 15 nm wall thickness. This nanotubular TiO₂ support provides a high surface area and it significantly enhances the electrocatalytic activity of Pt/Ru for methanol oxidation (relative to the performance of Pt/Ru at the same loading but immobilized on a conventional compact TiO₂ support). Annealed to anatase, the TiO₂ nanotubular support exhibits even higher enhancement effect during electrooxidation of methanol than when used in the “as-formed” amorphous structure. The overall electrocatalytic activity of the system can be further increased by illumination with UV-light (wavelength 325 nm).     

Low temperature catalytic conversion of methane to formic acid by simple vanadium compound with use of H2O2

Selective oxidation of methane with hydrogen peroxide was catalyzed by several simple vanadium compounds in CH3CN. The reaction could afford formic acid as the major product. Vanadyl oxysulfate (VOSO4) was found to be an efficient catalyst. Specifically, the selectivity to formic acid of 70% at a methane conversion of 6.5% could be achieved over the VOSO4 catalyst under the reaction conditions of methane pressure 3.0 MPa and temperature 333 K for 4 h. The UV-Vis spectroscopic measurements revealed that the formation of V5+ species during the reaction might be vital for the methane activation. The reaction probably proceeded via radical mechanism.     

Partial oxidation of methane to syngas catalyzed by a nickel nanowire catalyst

A nickel nanowire catalyst was prepared by a hard template method,and characterized by transmission electron microscopy (TEM),N2 physical adsorption,X-ray photoelectron spectrometry (XPS),X-ray diffraction (XRD) and H2 temperature-programmed reduction (H2-TPR).The catalytic properties of the nanowire catalyst in the partial oxidation of methane to syngas were compared with a metallic Ni catalyst which was prepared with nickel sponge.The characterization results showed that the nickel nanowire catalyst had high specific surface area and there was more NiO phase in the nickel nanowire catalyst than in the metallic Ni catalyst.The reaction results showed that the nickel nanowire catalyst had high CH4 conversion and selectivities for H2 and CO under low space velocity.     

Effect of Cu promoter on Ni-based SBA-15 catalysts for partial oxidation of methane to syngas

A series of Ni/SBA-15 catalysts with 5wt% to 15wt% Ni content as well as a series of 12.5%Ni/Cu/SBA-15 catalysts with 1% to 10% copper content were prepared by the impregnation method. The catalytic performance for partial oxidation of methane was investigated in a continuous flow microreactor under atmospheric pressure. The textural and chemical properties of the catalysts were characterized by XRD, TEM, BET and H2-TPR techniques. The results indicated that the catalysts modified with Cu promoter showed better performance than those without modification. For the 12.5%Ni/2.5%/Cu/SBA-15 catalyst, at 850 ◦C the conversion of CH4 reached 97.9% and the selectivity of CO and H2 reached 98.0% and 96.0%, respectively. In XRD patterns of the Ni/Cu/SBA-15 catalyst with 7.5 to 10% Cu contents there were CuO characteristic peaks beside NiO characteristic peaks. The mesoporous structure of SBA-15 was retained in all of the catalysts. TPR analysis of the catalysts revealed that a strong interaction between Ni, Cu promoter and SBA-15 support may be existed. This interaction enhanced significantly the redox properties of the catalysts resulting in the higher catalytic activity.     

Influence of the composition of composites based on Y-and Sc-stabilized zirconium dioxide on catalytic properties in the oxidative conversion of methane

The effect of the composition of composites based on Y-and Sc-stabilized zirconium dioxide doped with CeO₂ and transition metal (Cu, Co, Ni) oxides on catalytic properties in the oxidative conversion of methane was studied. The activity of the composites correlated with the quantity and mobility of oxygen in them. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 3, pp. 184–188, May–June, 2006.     

Direct oxidative esterification of toluene with 1,3‐dicarbonyl compounds catalysed by copper complex supported on magnetic nanoparticles

Toluene oxidation is one of the substantial industrial technologies since oxidized products are industrially very important intermediates. A Fe₃O₄@cysteine@Cu‐catalysed reaction that uses tert ‐butyl hydroperoxide as oxidant to produce esters from toluene and β‐diketones or β‐keto esters, enolate precursors, has been developed. Oxidative esterification of toluene with 1,3‐dicarbonyl derivatives led to C─O bond formation and direct C─H functionalization.     

Coke formation during high pressure catalytic partial oxidation of methane to syngas

Summary Carbonization of the surface of alumina-based catalysts has been studied with respect to the composition of the catalysts and conditions of the propionitrile ammonolysis. It was shown that the surface concentration of carbon increases with the increase in temperature and with time of the reaction and depends on the catalysts nature in the order: Al-Zr(5)-O < Al-Zr(40)-O < Al-O < Al-Mg-O. The surface concentration of the Brönsted acidic sites follows the same sequence.     

Direct partial oxidation of methane to methanol： Reaction zones and role of catalyst location

Direct partial oxidation of methane to methanol was investigated in a specially designed reactor. Methanol yield of about 7%-8% was obtained in gas phase partial oxidation. It was proposed that the reactor could be divided into three reaction zones, namely pre-reaction zone, fierce reaction zone, and post-reaction zone, when the temperature was high enough to initiate a reaction. The oxidation of methane proceeded and was completed mostly in the fierce reaction zone. When the reactant mixture entered the post-reaction zone, only a small amount of produced methanol would bring about secondary reactions, because molecular oxygen had been exhausted in the fierce reaction zone. A catalyst, if necessary, should be placed either in the pre-reaction zone, to initiate a partial oxidation reaction at a lower temperature, or in the fierce reaction zone to control the homogeneous free radical reaction.