Rate determining step methane

In a later publication, Kolbel et al. (K16) have proposed a less empirical model based on the assumption that the rate-determining steps for a slurry process are the catalytic reaction and the mass transfer across the gas-liquid interface. When used for the hydrogenation of carbon monoxide to methane, the process rate is expressed as moles carbon monoxide consumed per hour and per cubic meter of slurry ... 

At least when methane is the substrate, the rate-determining step is... 

Results discussed above show in several lines a distinct biomimetic-type activity of iron complexes stabilized in the ZSM-S matrix. The most important feature is their unique ability to coordinate a very reactive a-oxygen form which is similar to the active oxygen species of MMO. At room temperature a-oxygen provides various oxidation reactions including selective hydroxylation of methane to methanol. Like in biological oxidation, the rate determining step of this reaction involves the cleavage of C-H bond. 

The rate-determining step is the abstraction of the first hydrogen atom from molecu-larly adsorbed methane with the formation of an adsorbed methyl group. Based on this... 

The observation of extremely facile formation of an acetyl complex and the finding that oxidative addition is the rate-determining step are almost certainly related to the high selectivity observed in the reaction. Thus, the extremely short lifetime of any CH3—Rh species makes it unlikely that it would be reacted off to methane in the presence of hydrogen (and/or metal hydrides). 

Several authors have proposed that CH4 combustion over PdO occurs via a redox mechanism [82-85]. Methane activation through assisted hydrogen extraction is generally regarded as the rate-determining step, although there is not a general consensus on the nature of the adsorption sites. Further, desorption of H2O by decomposition of surface hydroxyls has been reported to play a key role in reaction kinetics at temperatures below 450 °C [67, 86]. 

Our presumption that the rate-determining step somehow produced a vacant coordination site led to our investigating the reaction in the presence of trieth-ylphosphine. Methane is still eliminated, Os(CO)4(Et3P) is formed, and the disappearance rate of Os(CO)4(H)CH3 is still first order in that material, but the rate constant (6.4 X 10-5 sec-1) is one-half that observed in the absence of Et3P. The rate is completely independent of the concentration of Furthermore,... 

Hence, (V111-58) is the rate-determining step for the ClO-Cl catalytic cycle. The chain-terminating step is the reaction with methane to form HCI... 

If the concerted four-center mechanism for formation of chloromethane and hydrogen chloride from chlorine and methane is discarded, all the remaining possibilities are stepwise reaction mechanisms. A slow stepwise reaction is dynamically analogous to the flow of sand through a succession of funnels with different stem diameters. The funnel with the smallest stem will be the most important bottleneck and, if its stem diameter is much smaller than the others, it alone will determine the flow rate. Generally, a multistep chemical reaction will have a slow rate-determining step (analogous to the funnel with the small stem) and other relatively fast steps, which may occur either before or after the slow step. 

In 1975 Vannice published a comprehensive study of the kinetics of the methanation of carbon monoxide over various metals.45 He analysed his results in terms of a rate-determining step for the reaction involving the interaction of adsorbed CHOH species and adsorbed H atoms ... 

Since the gas phase contains five components which should satisfy three elementary mass balances, two arbitrarily chosen, but independent,conversions are required to define its composition, e.g. the total methane conversion, Xqjj, and the conversion of methane into C02, Xco2 The prediction of these conversions in any point of the reactor therefore necessitates two rate equations, each derived under the assumption of at least one rate determining step (r.d.s.). A number of authors have used one rate equation only, thereby assuming the watergas shift reaction (CO+H2O Z C02+H2) to be at equilibrium at any point in the reactor (2, 3, 4), but others have contradicted this assumption (5, 6). From this mechanism and after discrimination between more than 150 rival models (1), the... 

In a related study, the complex Tp Pt (CH3)2H (TpMe2 hydridotris(3,5-dimethyl pyrazolyl)borate) undergoes reductive elimination of methane, but here labeling studies revealed that the rate-determining step is loss of methane from an intermediate methane a complex. Following loss of methane, the 16e intermediate complex can be... 

Examination of the power-law exponents presented here show that the rate of hydrogenation of CO to hydrocartx)ns and oxygenate is inhibited by CO over Rh/Al203 but not for methanol formation over Rh-Mo/Al203. Interestingly, the inhibition for CH4 and higher alcohols formation remains. The implication is that the mechanism of the rate determining step for methanol differs fiom methane and that the latter is dependent on the Rh. 

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