Chlorination of HCFC-133a with chlorine was performed over silica-supported NiCl₂, CuCl₂, MnCl₂, and KCl as well as over some activated carbons. The results were compared with those from the thermal chlorination and from other studies. The chlorides tested were found not to practically act as effective catalysts for the chlorination of HCFC-133a to HCFC-123 contrary to the claims in earlier works, and the activated carbons exhibited poorer HCFC-123 yields than the chlorides.