Title page for ETD etd-09182006-091123


Type of Document Dissertation
Author Minton, Mary Amanda
URN etd-09182006-091123
Title Reactions of Halogenated Ethylenes on the alpha-Cr2O3 (1012) Surface
Degree PhD
Department Chemical Engineering
Advisory Committee
Advisor Name Title
Cox, David F. Committee Chair
Dillard, John G. Committee Member
Hanson, Brian E. Committee Member
Morris, John R. Committee Member
Oyama, Shigeo Ted Committee Member
Keywords
  • vinylidene
  • chlorovinyl
  • vinyl
  • butadiene
  • ethylene
  • acetylene
  • halocarbons
Date of Defense 2006-09-07
Availability unrestricted
Abstract
The thermally induced reaction of halogenated ethylenes on the α-Cr2O3 (10 2) single crystal surface results in the formation of gas phase hydrocarbons including acetylene, ethylene, butadiene, and dihydrogen, and deposition of surface chlorine adatoms. No surface carbon or combustion products are observed in any reactions indicating no thermally induced C-C bond cleavage occurs and surface lattice oxygen is not incorporated into surface intermediates. Thermal desorption spectroscopy indicates that in all halogenated ethylene reactions acetylene is the major product, regardless of the reaction scheme. The surface reactions of halogenated ethylenes are proposed to proceed through C-X (X=halogen) bond cleavage to form surface halogen adatoms and surface C2 hydrocarbon fragments. Halogen adatom deposition affects reaction barriers to hydrocarbon formation, and eventually shuts down surface chemistry. Photoemission and near edge x-ray absorption fine structure spectra show that all studied reactants undergo some C-X bond cleavage upon low temperature adsorption forming adsorbed C2 fragments and halogen adatoms. Photoemission for each reaction system shows at least two C1s features (283.0-286.0 eV) and two Cl2p features (2p3/2=198.0-201.0 eV) with higher binding energy features associated with molecularly intact halogenated ethylenes and lower binding energy features associated with dissociated surface species. Near edge x-ray absorption fine structure spectra taken, corresponding to photoemission spectra, indicate the occurrence of C1s→π* transitions, indicating intact p-systems are present. Heating the surface results in a reduction in intensity of higher energy photoemission and near edge x-ray absorption fine structure indicative of a decrease in surface C-X bonds.
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