Methane dimerization

Jorgensen W L, J K Buckner, S Boudon and J Tirado-Reeves 1988. Efficient Computation of Absoluti Free Energies of Binding by Computer Simulations - Applications to the Methane Dimer ir Water. Journal of Chemical Physics 89 3742-3746. 

WL Jorgensen, JK Buckner, S Boudon, J Tirado-Rives. Efficient computation of absolute free energies of binding by computer simulations. Application to the methane dimer m water. J Chem Phys 89 3742-3746, 1988. 

Two series of catalysts were synthesized for subsequent evaluation as methane dimerization catalysts. The first series was alkali modified zinc oxide (6) and magnesium oxide catalysts (7), which were reported to be active for methane activation, while the second series was ion modified perovskites described by Machida and Enyo (8). The objective of the present study was to determine whether the aerosol technique could provide a wide range of ion substitutions as homogeneous solid solutions, and to determine whether moderately high surface area catalysts could... 

Methane dimerization catalysts in the perovskite substitutional series SrCe j. x)YbxO(3 x/2) where x was varied from 0.0 to 1.0 were synthesized by the HTAD process. These same catalysts were synthesized by Machida and Enyo (8) by fusion... 

Estimate the cost of nonbonded HH repulsion as a function of distance by plotting energy (vertical axis) vs. HH separation (horizontal axis) for methane+melham (two methanes approaching each other with CH bonds head on ). Next, measure the distance between the nearest hydrogens in eclipsed ethane. What is the HH repulsion energy in the methane dimer at this distance Multiplied by three, does this approximate the rotation barrier in ethane ... 

Pulse electron-beam mass spectrometry was applied by Kebarle, Hiraoka, and co-workers766,772 to study the existence and structure of CH5+(CH4) cluster ions in the gas phase. These CH5+(CH4) clusters were previously observed by mass spectrometry by Field and Beggs.773 The enthalpy and free energy changes measured are compatible with the Cs symmetrical structure. Electron ionization mass spectrometry has been recently used by Jung and co-workers774 to explore ion-molecule reactions within ionized methane clusters. The most abundant CH5+(CH4) cluster is supposed to be the product of the intracluster ion-molecule reaction depicted in Eq. (3.120) involving the methane dimer ion 424. 

Ravishanker G, Mezei M, Beveridge DL (1982) Monte Carlo simulation study of the hydro-phobic effect. Potential of mean force for aqueous methane dimer at 25 and 50 °C. Farad Symp Chem Soc 17 79-91... 

Sherrill, C. D. Takatani, T. Hohenstein, E. G. An assessment of theoretical methods for nonbonded interactions comparison to complete basis set limit coupled-clusta-potential enragy curves for the benzene dimer, the methane dimer, benzene—methane, and benzene—H2S, / Phys. Chem. A 2009,113,10146-10159. 

A wide variety of metal oxides were screened by Keller and Bhasin in their pioneering investigation into methane dimerization. Since then, many catalysts have been developed and tested (2-6). However, due to the thermal stability of methane, even in the presence of oxidizers, conversion is extremely low. To date, total yields of C2 products of 15 to 207. 2, 4) are considered high. 

Many different types of catalysts have been employed, including both metal oxides, such as PbO (5-7), which react in a redox cycle to Pb metal, and catalysts containing metals with fixed valence, such as Li promoted MgO (jg), which produce active Li 0" sites for methane dimerization. Such catalysts were discussed in four papers at the recent Ninth International Congress on Catalysis 8)- The most effective catalysts have several common traits. Low surface area has been found to be very important 2 9) in the conversion of methane. Also of importance is the basicity of the catalyst. (However, not every basic material causes C2 formation.)... 

E. Fraschini and A. J. Stone, /. Comput. Chem., 19, 847 (1998). H—H Model Potential for Exchange Repulsion Energy of Methane Dimer. 

The interest in the oxidative coupling reaction was initiated 10 years ago by the pioneering work conducted by Keller and Bhasin. Since then hundreds of papers have been published including review papers (references 2-4 to cite a few), proceedings from several synqx>sia on the subject, and a recent book which summarizes the state of research in several leading laboratories around the world. The objective of this survey is not to review the literature of methane coupling but rather to appraise certain aspects of methane dimerization that in the opinion of the authors are critical for the better understanding of the methane dimerization reacticm. As a result, the review is focused on selected topics and does not include many aspects which otherwise would have been included in broader literature review. The topics selected are as follows ... 

Morphological, kinetic, and thermodynamic aspects of catalytic methane dimerization. 

A general mechanism of the oxidative coupling of methane over reducible oxide catalysts has been proposed by Lee and Oyama. Their reaction sequence is based on the cracking mechanism suggested by Kolts and Delzer which was adapted to the methane dimerization process. The similarities between these two processes as indicated by Lee and Oyama were as follows (1) the same materials (Mn/MgO, Fe/MgO, LajOj, Ce02) are active in both reactions,... 

It is assumed that this is also a rate determining step for the overall reaction. The activation energy of reaction (4) and the site density of oxygen active centers were the only adjustable parameters of the model. In general, a C-H bond scission for reactants and products of the methane dimerization process occurs by an Eley-Rideal (E-R) type mechanism to form a gas-phase alkyl radical and a hydroxyl surface site (HO ) ... 

Other steps used in the model assume that the heterogeneous conversion of methane is limited to the gas-phase availability of oxygen, O2 adsorption is fast relative to the rate of methane conversion, and heat and mass transports are fast relative to the reaction rates. Calculations for the above model were conducted for a batch reactor using some kinetic parameters available for the oxidative coupling of methane over sodium-promoted CaO. The results of the computer simulation performed for methane dimerization at 800 °C can be found in Figure 7. It is seen that the major products of the reaction are ethane, ethylene, and CO. The formation of methanol and formaldehyde decreases as the contact time increases. 

Novoa, J. J., Whangbo, M.-H. and Williams, J. M. (1991) Interaction energies associated with short intermolecular contacts of C-H bonds. II Ab initio computational study of the C-H- - -H-C interactions in methane dimer, J. Chem. Phys. 94, 4835 841. 

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