The dechlorination of chloroethane and 1,1-dichloroethane have been used to produce ethyl (CH₃CH₂–) and ethylidene (CH₃CH=) intermediates on a model chromia surface.  Thermal desorption studies indicate that ethyl intermediates decompose via a 1^st-order, rate-limiting, β-hydride elimination step to produce ethylene, ethane, and H₂ products in the gas phase.  Ethylidene intermediates produce ethylene as the sole gas phase product.  The lack of H₂ production from ethylidene suggests that no hydrogen atoms are transferred to the surface, and indicates an intramolecular isomerization of ethylidene to ethylene.  Neither intermediate produces a measurable amount of surface carbon, consistent with earlier observations of a high selectivity of this surface for the conversion of C2 surface intermediates to gas phase products without significant coke formation.  In both cases, deposited chlorine adatoms bind at surface Cr cation sites, and lower the reactivity of the surface by simple site blocking.