Infrared Spectroscopic Study of the Adsorption and Dissociation of CH2Cl2 on Pd/SiO2. Generation of CH2 Species

Article abstract of DOI:10.1006/jcat.1995.1189

The adsorption and dissociation of CH2Cl2 have been investigated by means of infrared spectroscopy combined with mass spectrometry.CH2Cl2 adsorbs molecularly on Pd/SiO2 at low temperature (193-213 K) and interacts strongly with the OH groups of silica to from H-bridge-bonded methylene halide.This is exhibited by a significant attenuation of the 3744 cm^-1 band exhibited by silica and by the development of a broad spectral feature at 3662 cm^-1.The dissociation of CH2Cl2 was observed at 233-243 K.The primary product of dissociation, CH2, was characterized by absorption bands at 2984 and 2907 cm^-1.The CH2 species dimerized into C2H4 above 263 K.A fraction of ethylene desorbed, while another fraction was transformed into ethylidyne.The latter compound is characterized by absorption bands at 2922 and 2857 cm^-1.By means of mass spectrometry C2H4 and HCl were identified in the desorbing gases at 250-330 K.Decomposition of CH2Cl2 occurred above 350 K yielding C2H4, CH4, HCl, and H2O.Some exploratory measurements were also performed with CH2I2.