In situ infrared observation during the reduction of NO by CH4 over Co-ZSM-5 reveals the presence of CN species. The reactivity of these species has been probed by exposing them to NO2, O-2, or NO while monitoring their rate of disappearance. In a complementary set of experiments, mass spectrometry was used to identify the reaction products as N-2 and CO2. At 450 degrees C the rate coefficients for the consumption of CN are 8.5 x 10(-5), 1.9 x 10(-6), and 3.3 x 10(-7) s(-1) ppm(-1) for reaction in NO2, O-2, and NO, respectively. The reactivity of CN is sufficiently high for these species to be considered reaction intermediates in the formation of N-2 and CO2 during the reduction of NO by CH4 in the presence of O-2.