The impact of the surface heterogeneity of two commercial V2O5–WO3/TiO2 catalysts on the NH3–SCR–DeNOx process was investigated by kinetic modelling of the surface elementary steps. It was demonstrated that transient kinetic is sufficiently qualified to investigate the heterogeneity of catalytic active sites. In this context, possible deviations of the Langmuir adsorption isotherm formula were analyzed which still show a satisfactory deviation at temperatures below 623 K whereas the deviation increases rapidly at T > 623 K.