Infrared (IR) spectroscopic investigations were performed of the adsorption and surface reactions of CH3Cl over acidic, basic and neutral zeolite catalysts. In each case, the spectral changes reflected the appearance of the Fermi resonance phenomenon. The resonance parameters determined pointed to a decreasing extent of resonance in consequence of the adsorption. No influence of the acidity of the adsorbents was observed. The formation and consumption of HCl and OH groups were established at elevated temperatures. The reactions assumed to have occurred are described and explained.