Coupling reactions, of methane

Cerium oxides are outstanding oxide materials for catalytic purposes, and they are used in many catalytic applications, for example, for the oxidation of CO, the removal of SOx from fluid catalytic cracking flue gases, the water gas shift reaction, or in the oxidative coupling reaction of methane [155, 156]. Ceria is also widely used as an active component in the three-way catalyst for automotive exhaust pollution control,... 

Methane and Toluene to Styrene Basic catalysts in the presence of oxygen and/or air are reported to be attractive catalysts for this reaction. Most research was performed in the late 1980s and early 1990s. The fundamentals resemble the oxidative coupling reaction of methane to ethylene. 

A final example of the role of additives is that of Larkins and Nordin.25 L12CO3 when added to MgO catalysts increases the selectivity to C2 hydrocarbons in oxidative coupling reactions of methane as has been found by others. Catalytic, scanning electron microscopy, X-ray powder diffraction, temperature programmed reactions and electron microprobe studies have been used to show that additives of both Zn and Mn can enhance selectivity to C2 hydrocarbons in these systems. 

As can be seen from the above equation, formation of HCN is in reality a hetero-bimolecular oxidative coupling reaction of methane with ammonia. The ammoxidation reactor construction is a simple fixed-bed multi-tube and the catalyst is usually a platinum or sometimes a Group V or VI metal oxide on a silica or alumina support. The HCN product is recovered by condensation and fractionation. With the reaction simplicity and yield, and widespread availability of starting materials, in-situ HCN generation is an ideal industry solution to HCN supply. (See Chapter 29 for more details.)... 

Density functional theory and MP2 calculations of the transition states and reaction paths on coupling reaction of methane through plasma108... 

Other Selected Studies. In addition to the work by ARCO and UCC, numerous catalysts (mostly metal oxides of various groups, singly or mixed, promoted or unpromoted, with or without supports) have been explored for oxidative coupling reaction of methane by a number of researchers in different countries. To... 

Many metal oxides are able to perform the oxidative coupling reaction of methane molecules. Methane can also be directly converted with oxygen via oxidative coupling (OCM) into ethane and ethylene according to the following reaction ... 

The key intermediate in another total synthesis of secoquettamine (234), elaborated by Stevenson et al. (185), was 2-arylbenzofuran 241 prepared by a coupling reaction of the copper salt of 4-benzyloxyphenylacetylene with bromoisovanillin (Scheme 37). In the next step condensation with nitro-methane and reduction gave amine 242, which when N-methylated and debenzylated resulted in secoquettamine (234). 

H. Werner, M. E. Schneider, M. Bosch, J. Wolf, J. H. Teuben, A. Meetsma, and S. I. Troyanov, Cationic and Neutral Diphenyldiazomethanerhodium(I) Complexes as Cata-lytically Active Species in the C—C Coupling Reaction of Olefins with Diphenyldiazo-methane, Chem. Eur. J. 6, 3052-3059 (2000). 

Other applications have been proposed but as yet without success, like the direct coupling of methane to ethylene or the direct conversion of methane to methanol. Recently, some disclosures were made on the reaction of methane with alkanes to yield augmented alkanes. ... 

In the last decade attention has been paid to ethane ODH due to the interest in transforming an abundant component of natural gas into a more valuable product. It has been shown that catalysts based on Li and Mg mixed oxides, active in the reaction of methane coupling, are also active in ethane ODH [3-4], A similar behavior has been also found for various rare eairth oxides [5]. 

Recently we observed the effect which supports the conclusion about the substantial role of the radical reaction outside of the catalyst grains. When a very efficient OCM oxide catalyst (10% Nd/MgO) was placed into the reactor together with an inactive metal filament (Ni-based alloy) the sharp increase of conversion accompanied by the selectivity shift from oxidative coupling to the formation of CO and H2 was observed [19]. Since the metal component has a low activity also with respect to ethane oxidation, this behavior is not due to successive oxidation or decomposition of C2 hydrocarbons on the metal surface, but should be attributed to the reactions of methane oxidation intermediates. Almost total disappearance of ethane (which is a product of CH3 radicals recombination) and acceleration of the apparent reaction rate by the addition of an "inert material indicate that the efficiency of methane oxidative transformations can be substantially increased if the radicals have a chance to react outside the zone where they formed and the role of reaction (-1) decreases. Although the second (metal) surface is not active enough to conduct the reaction of saturated hydrocarbon molecules (methane and ethane), the radicals generated by the oxide can react further on the metal surface. As a result, the fraction of the products formed from methane activated in the reaction (1) increases, and the formation of the final reaction mixture of different composition takes place. 

Another reaction to be mentioned briefly is the Ta+-mediated coupling of methane and carbon dioxide to afford ketene the latter can serve as a precursor for acetic acid (Wesendrup and Schwarz 1995a,b). The rather attractive, yet hypothetical, coupling Reaction (7.11) is endothermic, however. In the mass spectrometric model study, the thermochemical driving force is provided by the oxidation of tantalum yielding the TaC>2 cation as the final product (Sandig and Koch 1998). Therefore, the coupled activation of methane and carbon dioxide so far remains stoichiometric ... 

On the other hand, the oxidative coupling reaction of CH4 in the presence of O2, even when performed in membrane type reactors,188 is mainly catalysed by metal oxides catalysts.185 Also, oligomerisation, aromatisa-tion, and the partial oxidation apply non-metallic heterogeneous catalysts (such as zeolites). The reader is therefore directed to some excellent reviews on these subjects.189,190 At this point, it is perhaps relevant to introduce the formation of carbon nanofibres or nanotubes from methane, these being catalysed by metal nanoparticles, but at this moment this is not considered as a Cl chemistry reaction. Again we direct the attention of the reader to some reviews on this type of process.191 192... 

Although gas-phase activation of methane by formaldehyde complexes has not yet been reported, transfer hydrogenations from several substrates to ketones and other coupling reactions of ligated formaldehyde have been observed [58]. 

Oxidative coupling of methane is the reaction of methane with an activated oxygen (active oxygen on a metal oxide catalyst in the present case) to form ethane and water. This reaction can occur in the absence of 02(g) with many reducible metal oxides 2-6,11,16... 

Thus, many groups have sought alternative oxidants. A polyoxometaUate (POM) has been shown to act as a mediator of oxidation by 0 (Equation 18.9). In this case, the reaction of methane with O in the presence of Periana s catalyst supported on HjPVjMOjjO j as acid and mediator of oxidation has been reported to form a mixture of methanol and acetaldehyde. The mechanism of the formation of the acetaldehyde product from methane is not firm, but is proposed to occur by oxidative coupling of methane with formaldehyde, which would be generated from methanol. These reactions occur with modest turnover numbers of about 30, but the use of and a POM is a clear advance over the original Shilov process with platinum(IV) as the stoichiometric oxidant. 

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