This research project is focused on understanding the reaction chemistry of intermediates possible in the dehydrogenation of ethane. The reactions of three C₂ alkyl surface intermediates over a-Cr₂O₃ single crystal surfaces has been examined for insight into the chemical details of the catalytic dehydrogenation of ethane over chromia. The a-Cr₂O₃ (1012) surface was selected because earlier work has shown that it is the predominantly exposed face on microcrystalline a-Cr₂O₃ powders.

Ethyl (CH₃CH₂C-), ethylidene (CH₃CH=) and ethylidyne (CH₃Cº) surface intermediates are readily formed from chloroethane, 1,1-dichloroethane and 1,1,1-trichloroethane, respectively, via C-Cl bond scission. In thermal desorption, the surface ethyl group reaction is initiated via a rate-limiting b-hydride elimination forming CH₂=CH₂ and surface hydrogen. Subsequently, two parallel competing reactions form CH₃-CH₃, via a-hydrogen addition to remaining surface ethyl groups, and H₂, via the combination of two surface hydrogen atoms. The reaction of ethylidene yields CH₂=CH₂ via a rate-limiting intramolecular isomerization reaction, as evinced by a lack H₂ desorption. The reaction of ethylidyne is initiated via a rate limiting b-hydride elimination forming vinylidene and surface hydrogen. Vinylidene undergoes an intramolecular isomerization reaction to CHºCH. Remaining ethylidyne intermediates undergo b-hydride addition to ethylidene which subsequently isomerizes to CH₂=CH₂. Remaining surface hydrogen adatoms combine to form H₂. The chlorine freed from the dissociation of the chlorocarbons binds at the five-coordinate surface Cr³⁺ sites on the stoichiometric surface and inhibits the surface chemistry via simple site blocking. No surface carbon deposition is observed from ethyl, ethylidene or ethylidyne intermediates and indicates these species are not likely coke formers in the dehydrogenation of ethane over (1012) facets of b-Cr₂O₃.