Pulse experiments over catalyst beds: A window of measurable reaction rate coefficients

The elimination of concentration profiles in porous catalyst pellets is not straightforward for transient kinetic experiments since profiles may arise from limited diffusion rates, but also from accumulation in the pellets. For TAP pulse experiments, dominated by Knudsen diffusion on the reactor scale, intrapellet diffusion is typically instantaneous for industrial catalysts. The Knudsen diffusivity for beds of porous pellets can be calculated from its value for non-porous pellets by accounting for the intrapellet porosity. The window of measurable rate coefficients is governed by a Damkohler number of the first type. A criterion is derived for experimental conditions, that allow intrinsic kinetic measurements with porous catalysts. The size of the admitted pulse should be sufficiently large to avoid pulse depletion by adsorption.