Catalytic activity and selectivity on heterogeneous surfaces with mass transfer

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Abstract
Effective reaction rates and selectivities on surfaces having active and inactive regions are calculated for systems in which diffusion of reactants and products through a boundary layer is significant. With a single reaction it is shown that rates are larger than those calculated assuming area weighted averages. The selectivity of production of an intermediate in a series of reactions on a heterogeneous surface is higher than on a homogeneous surface, and with parallel reactions selectivities may be lower or higher depending on the kinetics of the competing reaction.Numerical examples from NH3 oxidation on a Pt gauze and CO oxidation in the automotive converter indicate that these effects may be important in determining selectivities and conversions in some industrial reactors.