A previous one-dimensional model of the SCR monolith reactor has been extended to include the treatment of the undesired SO 2 oxidation reaction. A redox rate expression has been fitted to data, which accounts for the variable order of SO 2 , the asymptotic zeroth order behavior with respect to O 2 , the inhibiting effects of water and ammonia and the slight promoting effect of NO. The complete model successfully reproduces the interaction between DeNO x and SO 2 oxidation reactions, as evidenced by the match between the experimental and predicted dependences of SO 2 conversion on the NH 3 /NO feed ratio. Applications of the model to catalyst design are investigated. The optimal monolithic SCR catalysts have very thin walls, large fractions of macropores to promote diffusion of NO and NH 3 , but low specific surface areas to prevent SO 2 oxidation. According to a dedicated analysis, under industrial conditions it is not possible to modify the catalyst morphological properties in order to induce an NH 3 excess inside the catalyst to inhibit SO 2 oxidation.