A multisite kinetic model has been developed to represent ammonia selective catalytic reduction (NH3-SCR) behavior. The performance of copper-based chabazite catalyst CuSAPO-34 synthetized by ionic exchange method is studied under different dynamic operating conditions, characteristic to the DeNOx process. The model has the distinction of considering four active sites of different nature, allowing specific interpretation of the catalyst active phase function and, also, estimation of the relevant kinetic parameters. The adsorption/desorption of species on each site is described by a nonequilibrium model. The proposed optimized reaction mechanism includes the key reaction pathways found in standard catalytic SCR behavior: competitive adsorption of ammonia and water molecules on each site, the impact of low temperature water and corresponding hydroxyl intermediate formation on copper species, and the nitrite intermediary route. This multisite model enables the nonequilibrium representation of catalytic Cu-SAPO-34 behavior under different operating profiles, including fast and slow temperature modification in accordance with the different site configurations.