PULSE EXPERIMENTS OVER CATALYST BEDS - A WINDOW OF MEASURABLE REACTION-RATE COEFFICIENTS

The elimination of concentration profiles in porous catalyst pellets i s 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 diffusio n on the reactor scale, intrapellet diffusion is typically instantaneo us for industrial catalysts. The Knudsen diffusivity for beds of porou s pellets can be calculated from its value for non-porous pellets by a ccounting for the intrapellet porosity. The window of measurable rate coefficients is governed by a Damkohler number of the first type. A cr iterion is derived for experimental conditions, that allow intrinsic k inetic measurements with porous catalysts. The size of the admitted pu lse should be sufficiently large to avoid pulse depletion by adsorptio n.