INFECTED ZONE MODEL .1. A CONCEPT FOR CATALYST DEACTIVATION BY POISONING

An Infected Zone Model (IZM) was developed to correlate the decay in activity with the amount of poison covering a catalyst under conditions of chemical poisoning. This model is based on the transformation of normal sites into completely deactivated and infected sites when poison interacts with sites. "Normal" sites are not under the influence of poison. "Completely deactivated sites are those occupied by poison, while "infected sites are those influenced but not occupied by poison; both contribute to the total loss in activity. The following equation, which is obtained through balancing the activities of these sites on a catalytic surface, correlates the normalized activity a of catalysts with poison coverage theta: a = {1 - (1 - gamma(I)) [1 - (1 - theta) delta0]} (1 - theta), where gamma(I) is the average residual activity coefficient of infected sites, and delta0 is the effective infected zone size.