The formation and reactions of radicals on surfaces /
Surface-generated gas-phase radicals play an important role
| Main Author: | |
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| Format: | Thesis Book |
| Language: | English |
| Published: |
[Place of publication not identified] :
[publisher not identified] ;
1994.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=741966381&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Surface-generated gas-phase radicals play an important role in the partial oxidation of hydrocarbons. By monitoring these radicals using a matrix isolation electron spin resonance spectroscopy (MIESR) technique, the reaction mechanism and kinetics over metal oxides can be addressed. The correlation among CH4 conversion, CH3- radical production and lithium loading supports the conclusion that gas-phase CH3- radicals play a role in the oxidative coupling of methane (OCM) over Li'/MgO catalysts. There is no unique rate-limiting step in the formation of CH3- radicals over Li'/MgO using 02 as the oxidant. C02 was found to poison the basic oxygen ions that are responsible for the activation of methane over Li'/MgO and Sr/La2O3 catalysts. Modified catalysts, such as Cl/Li/MgO and Sb/Sr/La2Oi, were less subject to C02 poisoning. The presence of dopants, such as Cland Sb 31 ions, may modify the basicity of the catalysts so that they are no longer function as strong basic oxides. Considering the importance of CH3- radicals in the OCM reaction, the studies of their reactions with metal oxides provide not only an understanding of the catalytic oxidation process, but also information that will be useful for catalyst design and improvement. Methyl radicals were found to be highly reactive toward CeO2 and ZnO with or without the presence of 02, which is consistent with the fact that these are totally nonselective oxidative coupling catalysts. The addition of 02 or C02 to the reagent gases had a marked effect on the CH3radical reactivity for several selective oxidative coupling catalysts; whereas the addition of CH4 or N20 had little effect. CH3- radicals reacted extensively in porous materials, but no stable products were observed. Gas- phase benzyl radicals were produced during the reaction of toluene over Li'/MgO, Sr/La2o3 and SM203 catalysts. A selective cross-coupling catalyst, such as Li'/MgO, is a good benzyl radical generator, indicating the involvement of these radicals in the formation of C8 products. In the reaction of methane with propylene, both gas-phase methyl and allyl radicals were detected, and these are believed to be important intermediates for C4 formation. |
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| Item Description: | Vita. "Major Subject: Chemistry". |
| Physical Description: | xiii, 146 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references. |