The adsorption of HCN and the reaction of HCN with NO2 over Na-, and Ba-Y,FAU zeolite catalysts were investigated using in situ FTIR and TPD/TPR spectroscopies. Both catalysts adsorb HCN molecularly at room temperature, and the strength of adsorption is higher over Ba-Y than Na-Y. Over Na-Y, the reaction between HCN and NO, is slow at 473 K. On Ba-Y, HCN reacts readily with NO2 at 473K, forming N-2, CO, CO2, HNCO, NO, N2O, and C2N2. The results of this investigation suggest that initial step in the HCN + NO2 reaction over these catalysts is the hydrogen abstraction from HCN, and the formation of ionic CN- and NC-species. The formation of N2 can proceed directly from these ionic species upon their interaction with NO+. Alternatively, these cyanide species can be oxidized to isocyanates which then can be further transformed to N-2, N2O and COx in their Subsequent reaction with NOx.