Area, production natural boundaries

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In heterogeneous catalysis the contact between the catalyst and the reactants at the phase boundary is of utmost importance. This contact is established by adsorption of the reactants on the catalyst surface, resulting in increased concentration of the reactants. Adsorption takes place in localized areas called active centers. The overall mechanism of heterogeneous catalysis involves (a) ma.ss transfer of the reactants from the fluid to the catalytic surface and of the products from the catalytic surface to the fluid (b) diffusion of reactants and reaction products into and out of the pores of the catalyst (c) activated adsorption of reactants and desorption of products at the interface and (d) surface reactions of adsorbed reactants to form chemically adsorbed products. Considering that each of these steps is quite complex in itself, the highly complicated nature of the overall mechani.sm can be appreciated. 

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