Steps of a Catalytic Heterogeneous Reaction

Before discussing the influence of ultrasound on a catalytic heterogeneous reaction (liquid/solid, liquid/gas/solid, liquid/liquid/solid), it is useful to illustrate the steps through which such reactions can proceed. Let us refer to a very simple reaction transforming starting material SM to product P as illustrated in Fig. 6. For the sake of simplicity, we suppose that SM and P are both liquids or gases and that these substances are diluted in inert liquids or gases, respectively. 

1 external diffusion of SM through the solid-fluid interphase to the external part of the solid catalyst particle  

4 catalytic reaction from SM producing P species adsorbed on the catalyst  

6 internal back-diffusion of P through the pores of the catalytic particle  

7 external back-diffusion of P in the limit layer and collection of this product in the liquid or gas phase of the reactor. 

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