The present invention relates to a process for the preparation of haloethylenes, and preferably perhaloethylenes, by the gas-phase dechlorination of haloethanes in the presence of a catalyst and optionally in the presence of an alkene or an alkane. In particular aspects, the invention relates to a gas-phase process for preparing chlorotrifluoroethylene (CTFE). More particularly, the present invention relates to a gas-phase process for preparing CTFE from 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) by dechlorination in the presence of an alkene or an alkane and a catalyst.