(694f) Dead Zones in Reactive Porous Materials

This talk examines the conditions under which a dead zone, or a portion of a catalyst (or any reactive porous material) devoid of reactant, can form in a porous catalyst (material) in which simultaneous reaction and diffusion are occurring. The condition that allows for the existence of a dead zone is defined by a critical Thiele modulus. When the Thiele modulus ? the ratio of chemical reaction to diffusion - is greater than the critical Thiele modulus, a dead zone exists. This dead zone can be mathematically defined by a change of boundary conditions. We examine nth order reactions in isothermal infinite slabs, infinite cylinders, and spheres, demonstrating analytical expressions for concentration profiles and efficiency factors for zero order reactions in infinite cylinders and spheres. In addition, we provide analytical concentration profiles and efficiency factors for zero-order reactions in non-isothermal infinite slabs (in the so-called low beta approximation). We also discuss some common errors and misconceptions associated with this phenomenon.