Reactions of ethylidene on a model chromia surface: 1,1-dichloroethane on stoichiometric α-Cr2O3 (102)

The reaction of CH3CHCl2 over the nearly-stoichiometric α-Cr2O3 (10 1 ¯ 2) surface produces an ethylidene intermediate that yields primarily gas phase CH2══CH2 and surface chlorine adatoms; however, trace amounts of HC≡CH, CH3CH3, H2 and CH3CH══CHCH3 are also observed. A rate-limiting intramolecular isomerization (2,1-hydrogen shift) in the surface ethylidene species produces gas phase CH2══CH2. The chlorine freed from the dissociation of CH3CHCl2 binds at the five-coordinate surface Cr3+ sites on the stoichiometric surface, completing the octahedral coordination sphere, and inhibits the surface chemistry by simple site blocking. No surface carbon deposition is observed from the thermal reaction of 1,1-dichloroethane under the conditions of this study, demonstrating that the ethylidene intermediate is not a primary coke forming intermediate over (10 1 ¯ 2) facets of α-Cr2O3 under the conditions of this study.