Individual Steps in Heterogeneous Catalysis

Heterogeneously catalyzed reactions are composed of purely chemical and purely physical reaction steps. For the catalytic process to take place, the starting materials must be transported to the catalyst. Thus, apart from the acmal chemical reaction, diffusion, adsorption, and desorption processes are of importance for the progress of the overall reaction. 

We will now consider the simplest case of a catalytic gas reaction on a porous catalyst. The following reaction steps can be expected (Fig. 5-1) [T20,T26]  

1) Diffusion of the starting materials through the boundary layer to the catalyst surface. 

7) Diffusion of the products away from the catalyst through the boundary layer and 

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