Catalytic reactions of N2O in Cu-exchanged silica zeolites (ZSM-5) have been investigated theoretically using first-principles density functional theory (DFT). We consider four possible reaction paths for the production of N-2, including (i) ZCu + N2O ZCuO + N2, (ii) ZCuO + N2O --> ZCUO(2) + N-2, (iii) ZCu + NO + N2O --> ZCuNO(2) + N2 and (iv) ZCu + NO2 + N2O --> ZCuNO(3) + N-2 ("Z" refers to zeolites). Reactions (i) and (iii) are found to be the most favorable, whereas reactions (ii) and (iv) have much larger barriers. The implication for N2O reactions in non-selective reduction of NO by CO is also discussed.