Two principles for describing catalyst deactivation are discussed, one base
d on the deactivation mechanism and the other based on the activity and cat
alyst age distribution. When the model is based upon activity decay, it is
common to use a mean activity developed from the steady-state residence tim
e distribution. We compare control-relevant properties of such an approach
with those of a model based upon the deactivation mechanism. Using a contin
uous stirred tank reactor as an example, we show that the mechanistic appro
ach and the population balance approach lead to identical models. However,
common additional assumptions used for activity-based models lead to model
properties that may deviate considerably from the correct one.