Direct study of the catalytic decomposition of chlorine and chloromethanes over carbon films

The decompositions of chlorine and chloromethanes over pyrolytic carbon surfaces have been studied by modulated beam mass spectrometry in a low-pressure flow reactor between 850–1280 K. Whereas CH_3Cl is thoroughly stable, molecular chlorine readily dissociates by a first-order process with an activation energy about a half of its bond energy. The decompositions of CH_2Cl_2 and CCl_4 over clean silica surfaces initially display marked autoacceleration associated with the formation of soot on reactor walls and reach limiting rates which are much faster than those predicted for their homogeneous pyrolysis under the same conditions.