Effect of carbon dioxide on the activation energy for methyl radical generation over Li/MgO catalysts
- Texas A&M Univ., College Station, TX (United States); and others
The apparent activation energies for both the generation of CH{sub 3}{sup {sm_bullet}} radicals and the overall consumption of CH{sub 4} during the oxidative coupling reaction are strongly influenced by the presence of CO{sub 2}. The intrinsic activation energy for the information of CH{sub 3}{sup {sm_bullet}} radicals over Li/MgO catalysts is 26 {plus_minus} 2 kcal/mol, a value that increases to 37 {plus_minus} 3 kcal/mol upon the addition of only 0.04 Torr of CO{sub 2} to the reagents. The activation energy approaches a limiting value of ca. 50 kcal/mol at a CO{sub 2} partial pressure of {ge}1 Torr. Thus, under typical catalytic reaction conditions for the oxidative coupling of methane (e.g., 190 Torr of CH{sub 4}, 95 Torr of O{sub 2}), sufficient CO{sub 2} would be produced to attain this limiting value of E{sub a}. However, by operating at sufficiently low partial pressures and conversion levels, an E{sub a} of 32 kcal/mol was obtained during the oxidative coupling reaction. Temperature-programmed desorption of CO{sub 2} from Li/MgO produces a peak at 630{degrees}C, which is consistent with the role of CO{sub 2} as a poison for the catalytic reactions. 15 refs., 4 figs.
- OSTI ID:
- 554927
- Journal Information:
- Journal of Physical Chemistry, Vol. 96, Issue 15; Other Information: PBD: 23 Jul 1992
- Country of Publication:
- United States
- Language:
- English
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