INFRARED SPECTROSCOPIC STUDY OF THE ADSORPTION AND DISSOCIATION OF METHYL HALIDES ON SILICA-SUPPORTED PD

The adsorption and dissociation of CH3Cl and CH3I have been investigated by means of infrared spectroscopy at 193-573 K. Both compounds adsorb molecularly on Pd/SiO2 at 193 K and interact strongly with the OH groups of silica to form H-bridge-bonded alkyl halides. This was exhibited by a significant attenuation of the absorption band at 3744 cm-1 and by the development of a broad spectral feature at 3607 cm-1. The absorption band due to adsorbed CH3 species, indicating the dissociation of CH3Cl, was detected first at 263 K and was eliminated above 373 K. Preadsorbed CO and O exerted no observable influence on the adsorption and dissociation CH3Cl. However, potassium additive promoted the dissociation and somewhat stabilized the CH3 group on the surface. The dissociation of CH3I occurred at lower temperature and to a greater extent than that of CH3Cl. © 1993 Academic Press, Inc.