Poisoning anti-selective

This equation shows that for fast reaction in which a poison is distributed homogeneously, activity will fall less than linearily with poison concentration. This type of poisoning might be called anti-selective. Physically this occurs because the reaction uses more of the internal surface of the less active poisoned catalyst. That is, the slower reaction on a poisoned catalyst penetrates deeper into the catalyst pellet. In Fig. 8 we plot the poisoning curves for these two limiting cases ho very large (Curve B) and ho very small (Curve A). For intermediate values of ho, intermediate curves would be obtained. We next consider the... 

The classical treatments of activity loss by poisoning by Thiele 2 and Wheeler support the above distinctions, since the poi on was not considered to have any influence upon the pore geometry or effective diffusivity. Uniform, non-uniform and anti-selective poisoning do give rise to a wide spectrum of deactivation behaviour, but the non-comprehensive capability of a theory of poisoning to explain deactivation when significant accumulation takes place, requires that new approaches be made. This is confirmed by several more recent observations. 

Cilostazol (Pletal), a selective inhibitor of PDE III, is used for the treatment of intermittent claudication, an occlusive disease of blood vessels in the legs, which causes pain on walking. It acts as a vasodilator and inhibitor of platelet aggregation. Warfarin, initially developed as a rat poison, and a number of similar compounds, are effective anti-clotting agents by their action as vitamin K antagonists. 

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