Catalytic activity and selectivity on heterogeneous surfaces with mass transfer



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.