Experimental determination of the equilibrium constant of the reaction CH₃ + O₂ ⇄ CH₃O₂ during the gas‐phase oxidation of methane

Abstract

For the experimental determination of the equilibrium constant of the reaction CH3 + 0 2 '5 CH302 (l), the process of methane oxidation has been studied over the temperature range of 706-786 K. The concentration of CH3O2 has been measured by the radical freezing method, and that of CH3 from the rate of accumulation of ethane, assuming that CzHs is produced by the reaction CH3 + CH3 -C2H6 (2). The equilibrium constant of reaction (1) has been obtained a t four temperatures. For the heat of the reaction the value AH& = -32.2 f 1.5 kcal/mol is recommended.

An Automated Thermochemistry Protocol Based on Explicitly Correlated Coupled-Cluster Theory: The Methyl and Ethyl Peroxy Families

“…This theoretical determination accounts for 41% of the variance and is consistent with a third-law analysis performed on the experimental data of Slagle and Gutman . A third-law analysis of Knyazev and Slagle yields a reaction enthalpy that is 2.3 kJ/mol above that reported by Slagle and Gutman and 4.3 kJ/mol above the HEAT345­(Q) value, but the statistical analysis carried out by ATcT increases the reported 2.1 kJ/mol error bar by a factor of 1.8 because it is mutually inconsistent with the HEAT345­(Q) determination, the earlier analysis of Slagle and Gutman, and two photoionization appearance energies of methylium from methyl peroxy. , Second-law analyses by Slagle and Gutman as well as Knyazev and Slagle yield values that are consistent with all three values, but their uncertainties are so large that these reactions do not appreciably contribute to provenance. , There is also a determination of the equilibrium constant of methyl peroxy and methyl from Khachatryan et al that is also consistent with these determinations . There are other theoretical determinations included in the network that are also consistent, but the distributed provenance of methyl peroxy across several consistent experimental determinations, in addition to the well-established enthalpy of formation of methyl and methylium, gives confidence that the heat of formation of methyl peroxy is well established in TN version 1.122q-pre.…”

“…59,60 There is also a determination of the equilibrium constant of methyl peroxy and methyl from Khachatryan et al that is also consistent with these determinations. 61 There are other theoretical determinations included in the network that are also consistent, but the distributed provenance of methyl peroxy across several consistent experimental determinations, in addition to the wellestablished enthalpy of formation of methyl and methylium, gives confidence that the heat of formation of methyl peroxy is well established in TN version 1.122q-pre. Our current computational results agree well with the HEAT-345(Q) results of Nguyen et al, 3 the ANL0 results of Klippenstein et al, 17 the CCSD(T) results of Shallcross et al, 53 and the results of ATcT TN version 1.122q-pre.…”

Thermochemical Properties (ΔfH°(298 K), S°(298 K), Cp(T)) and Bond Dissociation Energies for C1–C4 Normal Hydroperoxides and Peroxy Radicals

“…Matthews et al determined an enthalpy of formation of −30.1 ± 1 kcal mol –1 based on vibrational overtone excitation experiment. Enthalpy of methyl hydroperoxide from other studies is −30.7 ± 0.9 by Goldsmith et al, −30.95 ± 0.22 by Simmie et al, −31.8 by Lay et al, −30.67 by Sheng et al, −30.9 ± 0.7 Blanksby et al, and −33.0 by Khachatryan et al, (all in kcal mol –1 ). Overall the standard enthalpy data, between the respective stable molecules and radicals for the C 2 to C 4 hydroperoxides and radicals, shows better agreement.…”

Thermodynamic and Kinetic Study on Carbon Dioxide Hydrogenation to Methanol over a Ga3Ni5(111) Surface: The Effects of Step Edge

“…H 2 COO is the only species that adsorbs at a 4-fold hollow site containing three Ni atoms and one Ga atom. Hydroxymethoxy (H 2 COOH) has been observed experimentally as one of the products of methane oxidation 85 and was proposed as an intermediate in the process of CO 2 hydrogenation to CH 3 OH by Tang et al, 86 Grabow et al, 75 and Zhao et al 73 In this work, H 2 COOH is considered as an intermediate which prefers to adsorb at step edge bridge sites, with one O atom anchored to two Ni atoms. Dihydroxycarbene (COHOH), detected by spectroscopy in the process of oxalic acid dissociation, 87 was also proposed as one key intermediate in the process of CO 2 hydrogenation on YBa 2 Cu 3 O 7 catalysts.…”