Description
| Abstract: | The matrix isolation electron spin resonance (MIESR) technique was used to study the formation of gas phase CH₃[dot] radicals during the catalytic oxidative coupling of methane over metal oxides. The reactor system utilized in the study could be operated at low pressures (1 Torr) or at atmospheric pressure. The formation of CH₃[dot] radicals over Li/MgO catalyst was examined in detail. An apparent activation energy for CH₃[dot] radical formation over 7 wt % Li/MgO was determined to be between 24-28 kcal mol⁻¹. The CH₃[dot] radical formation rate exhibited zero order in oxygen pressure and 0.5-1.0 order in methane pressure when measured in the low pressure system. The abilities of the lanthanide oxides to generate CH₃[dot] radicals was also examined. The results showed that the catalytic activities for the abstraction of H-atoms were best related to the basicity of the oxides, with the most basic oxides being active. The low pressure MIESR results were in qualitative agreement with the flow reactor results which supports the role of gas phase CH₃[dot] radicals in the catalytic conversion of CH₄ to C₂H₆. For the alkali-doped MgO and CaO catalysts, the atmospheric results showed relatively good agreement between (relative C₂ yield)[superscript 1/2] and the relative CH₃[dot] production. This correlation suggests that under atmospheric conditions, gas phase CH₃[dot] radical coupling is an important pathway in the catalytic conversion of CH₄ to C₂H₆. Quantitative evidence for the importance of gas phase coupling of CH₃[dot] radicals during the oxidative coupling of CH₄ is presented. It is shown that at least 40% of the C₂H₆ produced over a 7 wt % Li/MgO catalyst could be accounted for by the coupling of gas phase CH₃[dot] radicals. A 2nd order rate constant for gas phase CH₃[dot] radical coupling of 1.1 X 10⁻¹¹ mL radical⁻¹s⁻¹ was measured at 670°C. |
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| Item Description: | Typescript (photocopy).
Vita. |
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| Physical Description: | xii, 130 leaves : illustrations ; 29 cm |
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| Bibliography: | Includes bibliographical references (leaves 122-129). |
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