The focus of this work is to investigate whether a previously developed microkinetic deactivation model for hydrothermally treated Fe-BEA as NH3-SCR catalyst can be applied to describe chemical deactivation of Fe-BEA due to phosphorous exposure. The model describes the experiments well for Fe-BEA before and after phosphorous exposure by decreasing the site density, representing deactivation of sites due to formation of metaphosphates blocking the active iron sites, while the kinetic parameters are kept constant. Furthermore, the results show that the activity for low-temperature selective catalytic reduction (SCR) is very sensitive to loss of active monomeric iron species due to phosphorous poisoning compared to high-temperature SCR. Finally, the ammonia inhibition simulations show that exposure to phosphorous may affect the internal transport of ammonia between ammonia storage sites buffering the active iron sites, which results in a lower SCR performance during transient conditions. (c) 2014 American Institute of Chemical Engineers AIChE J, 61: 215-223, 2015