Utilizing bimetallic catalysts to mitigate coke formation in dry reforming of methane

Dry reforming of methane(DRM) involves the conversion of carbon dioxide(CO₂) and methane(CH₄) into syngas(a mixture of hydrogen, H₂, and carbon monoxide, CO), which can then be used to produce a wide range of products by means of Fischer–Tropsch synthesis. DRM has gained much attention as a means of mitigating damage from anthropogenic greenhouse gas(GHGs) emissions to the environment and instead utilizing these gases as precursors for value-added chemicals or to...     

Catalytic conversion of methane to methanol over Cu-mordenite

Methane can be converted to methanol over copper-exchanged mordenite at 200 °C. Methanol could be recovered at the end of the reactor. This multi-step reaction opens the possibility for methane to methanol conversion in a closed catalytic cyclic reaction system.     

Catalytic oxidative coupling of methane

The catalytic oxidative coupling of methane was studied over alkali, alkaline-earth and rare-earth metal oxides at 973 K under atmospheric pressure in a continuous flow fixed bed reactor. The catalysts used were prepared by impregnation method. Four alkaline-earth metal oxides were used as support. The temperature dependence of the catalytic properties and the phase composition of the catalysts were also detected.

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, 973 - . . . .

     

Catalytic decomposition of methane to produce hydrogen: A review

The increasing demands of hydrogen and the recent discovery of large reserves of methane have prompted the conversion of methane to hydrogen.The challenges rais...     

Catalytic effect of zinc oxide on the reduction of barium sulfate by methane

Reduction of barium sulfate by methane was investigated in this work. The thermogravimetric method was used to obtain kinetic parameters of the reaction in the temperature range of 900–975 °C at atmospheric pressure. The kinetics of the reaction has been studied both in the absence and presence of zinc oxide as a catalyst. The conversion–time data have been interpreted by using the grain model, and the effect of catalyst on the kinetic parameters has been elucidated. It was found that zinc oxide acted as fairly strong catalyst for the reaction, especially at higher temperatures. At about 975 °C the reaction rate constant was increased more than 7 times by using 2% of zinc oxide. This enhancement in the rate constant is valuable for industries.     

Catalytic reaction of methane with carbon dioxide

High activities and selectivities of Ni on SiO₂ catalysts producing CO in the reaction of CH₄ with CO₂, have been obtained at relatively low temperatures. These aspects are considerably different from the activities or selectivities of other catalysts, and have been explained by assuming that the Ni on SiO₂ catalyst markedly suppresses carbon deposition.

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CO Ni SiO₂ CH₄ CO₂. , Ni SiO₂.

     

Catalytic carbon dioxide hydrogenation to methane: A review of recent studies

Recently,various efforts have been put forward on the development of technologies for the synthesis of methane from CO₂ and H₂,since it can offer a solution for renewable H₂ storage and transportation.In parallel,this reaction is considered to be a critical step in reclaiming oxygen within a closed cycle.Over the years,extensive fundamental research works on CO₂ methanation have been investigated and reported in the literatures.In this updated review,we present a comprehensive overview of recent publications during the last 3 years.Various aspects on this reaction system are described in detail,such as thermodynamic considerations,catalyst innovations,the influence of reaction conditions,overall catalytic performance,and reaction mechanism.Finally,the future development of CO₂ methanation is discussed.     

甲烷催化裂解制氢技术研究进展

综述了甲烷催化裂解制氢的机理、影响因素以及催化剂的失活与再生,对影响甲烷催化裂解活性的因素如催化剂种类、载体种类、反应条件等方面进行了详细的论述。     

Catalytic selective oxidation or oxidative functionalization of methane and ethane to organic oxygenates

Selective oxidation or oxidative functionalization of methane and ethane by both homogeneous and heterogeneous catalysis is presented concerning: (1) selective oxidation of methane and ethane to organic oxygenates by hydrogen peroxide in a water medium in the presence of homogeneous osmium catalysts, (2) selective oxidation of methane to formaldehyde over highly dispersed iron and copper heterogeneous catalysts, (3) selective oxidation of ethane to acetaldehyde and formaldehyde over supported molybdenum cat...     

Catalytic activity of Mn-substituted barium hexaaluminates for methane combustion

The catalysts of hexaaluminate (BaMnxAl12-xO19-δ , x = 1.0, 2.0, 3.0, 4.0) to be used in methane combustion have been successfully synthesized by co-precipitation method and supercritical drying. The crystalline structure and surface area of catalyst were characterized by X-ray diffraction (XRD) and nitrogen adsorption analysis of BET method. BET analysis revealed that the preparing and drying method proposed here provides stable materials with higher surface area of 51.4 m2/g in comparison to materials prepared using conventional ambient drying method for BaMnxAl12?xO19-δ calcined at 1200℃ under oxygen. XRD analysis indicated that formation of a pure single phase BaMnxAl12-xO19-δ occurred up to x = 3 in the case of Mn-substituted barium hexaaluminates. Incorporation of Mn in excess leads to BaAl2O4 phase formation. As far as the valence state of Manganese ions was concerned, the introduced Mn ions were either divalent or trivalent. The first Mn ions were introduced in the matrix essentially as Mn2 and only for BaMn3Al9O19-δ does manganese exist exclusively as Mn3 ; the higher the Mn concen- tration, the higher the proportion of Mn3 . Catalytic activity for methane combustion has been measured for Mn-substituted barium hexaaluminates, light-off temperature was observed in the 512-624℃ range. The highest activity was obtained for catalysts containing 3 Mn ions per unit cell, which reveals that the BaMnxAl12-xO19-δ catalyst was a promising methane combustion catalyst with high activity and good thermal stability. Temperature programmed reduction (TPR) under hydrogen has been used to correlate the catalytic activity with the amount of easily reducible species.     

Numerical study on soot removal in partial oxidation of methane to syngas reactors

The serious carbon deposition existing in catalytic partial oxidation of methane (CPOM) to syngas process is one of the key problems that impede its industrialization. In this study, 3-dimensional unsteady numerical simulations of the soot formation and oxidation in oxidation section in a heat coupling reactor were carried out by computational fluid dynamics (CFD) approach incorporating the Moss-Brookes model for soot formation. The model has been validated and proven to be in good agreement with experiment results. Effects of nozzle type, nozzle convergence angle, channel spacing, number of channels, radius/height ratio, oxygen/carbon ratio, preheat temperature and additional introduction of steam on the soot formation were simulated. Results show that the soot formation in oxidation section of the heat coupling reactor depends on both nozzle structures and operation conditions, and the soot concentration can be greatly reduced by optimization with the maximum mass fraction of soot inside the oxidation reactor from 2.28% to 0.0501%, and so that the soot mass fraction at the exit reduces from 0.74% to 0.03%.     

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.     

Catalytic activity of rare earth oxides in flameless methane combustion

The following rare earth oxides, which were prepared by the precipitation of hydroxides, were studied as catalysts for the reaction of complete methane oxidation: CeO₂, a hydrated phase of La₂O₃, Pr₆O₁₁, Tb₄O₇, and Gd₂O₃. The catalytic activities of the oxides were compared in terms of first-order reaction rate constants per unit surface area of the catalyst. With consideration for data on the reduction of CeO₂, Pr₆O₁₁, and Tb₄O₇, the previously proposed redox reaction mechanism on transition metal oxides was supported. The high activity of hydrated La₂O₃ was found, and it was hypothesized that, in this case, the process occurred by the mechanism of oxidative methane condensation followed by the rapid oxidation of the resulting intermediate products.     

Catalytic combustion of methane over iron- and manganese-substituted lanthanum hexaaluminates

A series of hexaaluminates, LaMnFe _x Al_11−x O_19−δ samples (x = 1, 2, 4, 6, 8) as new catalysts were prepared by carbonate precipitation and calcined at high temperature. Fe and Mn ions were used as active components to replace part of aluminum ions in the hexaaluminate lattices. The structures and properties of these samples were characterized by XRD, BET, and XPS. The series of hexaaluminates exhibited significant catalytic activity and stability at high temperature. The LaMnFe₂Al₉O_19−δ retains a larger surface area and shows a good activity in methane combustion.     

负载型Pd/SnO2催化剂低温催化甲烷燃烧

天然气储量巨大,被广泛应用于发电和工业窑炉等.甲烷作为天然气中最主要的成分,是氢碳比最高的碳氢化合物,其温室效应显著.因此,不完全燃烧所引起的CH4排放,不仅导致能源浪费,同时也可造成环境污染.与传统火焰燃烧相比,CH4催化燃烧具有更高的燃烧效率,并可显著地减少大气污染物(CO,NOx和未完全燃烧的烃类)的排放.贵金属Pd催化剂对CH4催化燃烧表现出优异的催化性能,其中Pd颗粒的尺寸、Pd的化学状态、载体性质及其与Pd之间的相互作用等对其活性有显著影响.本文以不同温度(600,800,1000和1200℃)焙烧所得SnO2为载体,通过等体积浸渍法制备了Pd/SnO2催化剂,研究了SnO2焙烧温度对CH4催化燃烧性能的影响.结果表明,所制备的SnO2均为锐钛矿结构,并且随着SnO2焙烧温度的升高,晶型愈加完美,晶粒尺寸显著增大.催化剂中引入的Pd以高分散形式存在,CH4催化燃烧反应活性随着载体SnO2焙烧温度的升高而显著提高,其中Pd/SnO2(1200)表现出最高的CH4燃烧活性,起燃温度和最低全转化温度分别为265和390℃.在反应温度为300℃时,Pd/SnO2(1200)上甲烷的反应速率是Pd/SnO2(600)的36倍.XPS等结果表明,随着SnO2焙烧温度的升高,Pd的化学状态也有所差异:对于低温焙烧的SnO2(<800℃),Pd以Pd4+的形式进入到SnO2晶格内;随着焙烧温度的升高(>1000℃),Pd以Pd2+物种的形式存在于载体表面.结合活性评价结果推测,Pd的化学状态可能并非是影响催化剂活性的最关键因素.TEM等结果表明,Pd/SnO2(1000)上PdO的(101)晶面与载体SnO2的(101)晶面相近,分别为0.2641 nm和0.2638 nm.O2-TPD和CH4-TPR结果表明,Pd/SnO2(1200)催化剂上单位Pd原子上O2的脱附量是Pd/SnO2(600)的3倍,单位Pd原子上CH4的消耗量比催化剂Pd/SnO2(600)高出45%.因此,PdO和SnO2在构型上存在的晶面匹配可提高催化剂对O2的活化能力.综上所述,SnO2和贵金属之间的晶格匹配有利于氧在Pd-SnO2界面的活化,同时载体SnO2中的晶格氧亦可以通过"氧反溢流机理"补充到表面PdO/Pd上,从而增强催化剂对O2的吸附和活化能力,并提高CH4催化燃烧反应性能.升高SnO2的焙烧温度可强化SnO2和贵金属之间的晶格匹配,从而使催化剂活性随着SnO2焙烧温度升高而增大.     

温和条件下甲烷在熔盐介质中的催化转化

利用硝酸根-硝酸钾(摩尔比0.62:0.38)的熔盐体系作反应介质,以CeO~2,Ce(SO~4)~2,Cu(CF~3CO~2)~2,Co(CF~3CO~2)等为催化剂,在160℃和6.0MPa条件下甲烷被氧化成丙酮和/或三氟醋酸甲酯。甲烷的氯化则可在含氯化铜的氯化铝-氯化钠(摩尔比1:1)的熔盐介质中进行,硫酸银的引入可提高甲烷转化率和一氯甲烷的选择性。     

Calcia-supported lanthanide oxides for methane oxidation II. Catalytic properties

Lanthanum and samarium oxides supported on CaO, prepared from lanthanide nitrates or oxides, have been tested for methane oxidation. Samples prepared from the oxides are more active for total oxidation. Those from nitrates lead mainly to C₂ and C₃.

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, CaO, , . , , , — C₂ C₃.