Oxidative coupling, methane over

Most of the current results on the selective oxidation of methane over metal oxide catalysts may be interpreted in terms of methyl radical chemistry. These radicals may either react with the oxides themselves to form methoxide ions or they may enter the gas phase. The methoxide ions on supported molybdena decompose to form formaldehyde or they react with water to yield methanol. On the basic oxides methoxide ions result in complete oxidation. Those radicals which enter the gas phase undergo typical free radical chemistry which includes coupling reactions to give ethane and chain branching reactions to give nonselective oxidation products. Secondary surface reactions, particularly with ethylene, also may result in complete oxidation. If further improvements in yields of partial oxidation products are to be achieved, ways must be found to more efficiently utilize the methyl radicals, both with respect to surface reactions and to gas phase reactions. In addition, if ethylene is the desired product, catalysts must be fine-tuned to the point where they will activate methane, but not ethylene. 

An interesting approach to the oxidative coupling of methane to higher hydrocarbons is shown in Fig, 32. High-temperature one- or two-step oxidations of methane over reducible metal oxides produce methyl radicals which condense to C2 hydrocarbons in the gas phase [61-65], Recent work has demonstrated selectivities to C2 and higher hydrocarbons of greater than 70% from methane at conversions of nearly 20% [66-69], Reports of both moderate- and low-temperature oxidation of methane to methanol have appeared in the patent literature [70-7A],... 

S. Seimanides, P. Tsiakaras, X.E. Verykios, and C.G. Vayenas, Oxidative Coupling of Methane over Yttria-doped Zirconia Solid Electrolyte, Appl. Catal. 68, 41-53 (1991). 

Two conqiletely different behaviors of oxidative transformation of methane, namely the Oxidative Coupling of Methane to C2 Hydrocarbons(OCM) and the Partial Oxidation of Methane to Syngas(POM), were performed and related over the nickel-based catalysts due to different modification and different supports. It is concluded that the acidic property favors keeping the reduced nickel and the reduced nickel is necessary for POM reaction, and the bade property frvors keeping the oxidized nickel and the oxidized mckel is necessary for OCM reaction. POM and OCM reactions proceed at different active sites caused by different... 

Oxidative Coupling of Methane over Praseodymium Oxide in the Presence and Absence of Tetrachloromethane... 

Conversion and C2+ selectivity for oxidative coupling of methane over praseodymium oxide in the presence and absence of TCM. 

Oxidative Coupling of Methane over Alkali-Promoted Simple Molybdate Catalysts... 

Marafee, A., C.-J. Liu, G. Xu, R.G. Mallinson, L. Lobban. (1997). An experimental study on the oxidative coupling of methane in a direct current corona discharge reactor over Sr/La203 catalyst. Industrial Engineering Chemistry Research 36 632-637. 

Unfortunately, these requirements have not yet fully been met for any catalytic reaction, although for some simple catalytic reactions reasonable approaches are known. Such reactions are the oxidation of CO over a supported Rh catalyst [46,47], ammonia synthesis over iron [48, 49], and the HCN synthesis over a Pt gauze catalyst. More recently Wolf [50] carried out a micro-kinetic analysis of the primary reaction steps in the oxidative coupling of methane and also related the rate... 

The industrially important direct methane conversion processes comprise oxidative coupling, reductive coupling including pyrolysis reactions, partial oxidation, halogenation and oxyhalogenation,26 and ammoxidation. Other direct conversions include alkylation, electrophilic substitution, and C-H bond activation over various complex and super acid catalysts. Several of these direct conversion technologies remain to be exploited to achieve their full commercial potentials. 

Redox Cycle During Oxidative Coupling of Methane over PbO—MgO—AI2O3 Catalyst... 

Beside the benefit of having less mass transfer resistance from the catalyst particles to the membrane, attachment of catalyst to the membrane is also preferred over a bed of catalyst in certain reactions where the contact between the reactant(s) and the catalyst is controlled. An example is the partial oxidation or oxidative coupling of methane [Eng and Stoukides, 1991]. In this case, the reaction conversion and selectivity have been observed to depend on the chemical form of the reactant oxygen and its rate of delivery to the reaction zone through the membrane. This approach has also been demonstrated through an analysis for utilizing a catalytically impregnated porous membrane tube as a catalyst for gas-liquid reactions [Harold et al. 1989]. 

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