Catalysts for oxidative coupling

Challa, G., Meinders, H. C. Copper-polymer complexes as catalysts for oxidative coupling reactions. J. Mol. Catal. 1977, 3,185-190. 

Copper-Polymer Complexes as Catalysts for Oxidative Coupling Reactions... 

STUDY ON THE ACTIVE SITE STRUCTURE OF MgO CATALYSTS FOR OXIDATIVE COUPLING OF METHANE... 

The analysis of critical phenomena, such as hysteresis and self-oscillations, gives valuable information about the intrinsic mechanism of catalytic reactions [1,2], Recently we have observed a synergistic behavior and kinetic oscillations during methane oxidation in a binary catalytic bed containing oxide and metal components [3]. Whereas the oxide component (10% Nd/MgO) itself is very efficient as a catalyst for oxidative coupling of methane (OCM) to higher hydrocarbons, in the presence of an inactive low-surface area metal filament (Ni-based alloy) a sharp increase in the rate of reaction accompanied by a selectivity shift towards CO and H2 takes place and the oscillatory behavior arises. In the present work the following aspects of these phenomena have been studied ... 

Influence of Metal Oxide-Support Interactions in Supported La-Promoted CaO Catalysts for Oxidative Coupling of Methane... 

Surface composition and reactivity of lithium-doped magnesium oxide catalysts for oxidative coupling were studied recently by Peng et al. Two lithium phases were observed on the surface. Also, as noted by Lee and Oyama, this lithium-doped magnesium oxide catalyst appears to be the only one for which the methane activation sites have been identified. 

The Institute of Gas Technology recently patented a boron/alkali metal- promoted, metal oxide catalyst for oxidative coupling of methane. The catalytic studies were performed between 700 and 820 °C. The best activity (21%) and selectivity (86%) were achieved using 1% Li/0.2% B promoted on MgO. 

It has been known for some time that ligands 27, 35, and 36 can be used for direct synthesis of oxidized Cu(I) chloride solutions which are useful catalysts for oxidative coupling processes (26,27). Amide and lactam ligands contain the nitrogen atoms of amines (which generally promote Cu(I) oxidation, see above) and also serve as crude models for the peptide link of proteins, which is the general environment of copper found in oxidases (28). 

Ruthenium has a rich chemistry of hydroarylation reactions [22], but it has also been used successfully by Milstein and coworkers [23] as a catalyst for oxidative couplings of the Fujiwara-Moritani type (Figure 4.12). Under an atmosphere of carbon monoxide (6 bar), various ruthenium precursors effectively promoted the reaction of acrylates (e.g., 4g) with benzene (2a) to give a 1 1 ratio of the (E)-cinnamate 5i and methyl propionate 12, rather than the expected hydroarylation product methyl 3-phenylpropionate. Added oxygen (2 bar) could partly take over the role of the reoxidant from the alkene, resulting in an increase in the incorporahon of the alkene into the cinnamate product, giving a ratio of up to 3 1 of the arylated to the reduced acrylate. 

Khodadadian, M., Taghizadeh, M., and Hamidzadeh, M. (2011) Effects of various barium precursors and promoters on catalytic activity of Ba-Ti perovskite catalysts for oxidative coupling of methane. Fuel Process. Technol, 92 (6), 1164-1168. 

Techniques for attaching such ruthenium electrocatalysts to the electrode surface, and thereby realizing some of the advantages of the modified electrode devices, have been developed.512-521 The electrocatalytic activity of these films have been evaluated and some preparative scale experiments performed. The modified electrodes are active and selective catalysts for oxidation of alcohols.5 6-521 However, the kinetics of the catalysis is markedly slower with films compared to bulk solution. This is a consequence of the slowness of the access to highest oxidation states of the complex and of the chemical reactions coupled with the electron transfer in films. In compensation, the stability of catalysts is dramatically improved in films, especially with complexes sensitive to bpy ligand loss like [Ru(bpy)2(0)2]2 + 51, 519 521... 

In keeping with the earlier format we aim to provide the readership with sufficient practical details for the preparation and successful use of the relevant catalyst. Coupled with these specific examples, a selection of the products that may be obtained by a particular technology will be reviewed. In the different volumes of this new series we will feature catalysts for oxidation and reduction reactions, hydrolysis protocols and catalytic systems for carbon-carbon bond formation inter alia. Many of the catalysts featured will be chiral, given the present day interest in the preparation of single-enantiomer fine chemicals. When appropriate, a catalyst type that is capable of a wide range of transformations will be featured. In these volumes the amount of practical data that is described will be proportionately less, and attention will be focused on the past uses of the system and its future potential. 

Craq002+ also acts as a catalyst for oxidations with O2 in the presence of HNO2. Radical coupling, this time with NO, is again an essential mechanistic step. The catalysis takes advantage of the demonstrated preference for an intermediate, Craq02 +, to react in two-electron, hydride-transfer steps with organic materials. Reactivity studies of potential intermediates in other systems may uncover new catalytic powers of LMOO species. 

Later studies demonstrated that cyclic operation was not necessary for the attainment of high product selectivities. High selectivities could be obtained on suitable catalysts with contemporaneously fed methane and oxygen in the continuous, catalyst-mediated oxidative coupling of methane. A large-scale catalyst screening... 

Supported versions of such silver-catalyzed, three-component couplings have been recently reported. Silver oxide on multiwall carbon nanotubes or on alumina,102 as well as silver-doped zeolites,103 proved to be efficient and reusable catalysts for such coupling reactions. In the former, water was used as solvent, while in the latter, no solvent was required, making it a truly green process. 

Cu compounds in solution are usually active catalysts for oxidation reactions because of the favorable redox potential of the Cu(II)/Cu(I) couple. 

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