Contaminant within porous system

Two kinds of poison distributions must be distinguished. One distribution is that along the catalyst bed, the other one is within the porous system of the catalyst. It may be reasonably anticipated that under most conditions there will be a gradient of contaminant concentration which decreases in the direction from inlet to outlet also that there will be a decreasing concentration of contaminants from the outer confines of each separate catalyst body inwards into the pore system. The contaminant distribution will, however, differ for different types of catalysts and contaminants. 

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