Patterns of intraparticle distribution of surface concentration due to irreversible adsorption in TAP multi-pulse experiments

Abstract

Information on non-uniform distribution of catalyst surface concentration of active species or catalyst activity during a TAP multi-pulse experiment is required for accurate interpretation of TAP response data. In this work, characteristics of intraparticle distribution of surface concentration due to first-order irreversible adsorption during a TAP multi-pulse experiment were theoretically investigated. The profiles of occupied fractional surface coverage ( θ) in each spherical catalyst pellet were numerically simulated from the first pulse experiment until the catalyst was saturated. Distribution of θ with gradual change after each consecutive pulse experiment was examined. It was found that the profiles of θ in all catalyst pellets at any axial coordinates in the catalyst bed are the same when compared at the same amount of gas uptake in the pellet although more gas pulses are required to reach the same amount of gas uptake for the pellet closer to the reactor exit. The development of distribution of θ therefore follows the same pattern for all catalyst pellets in the reactor. Calculation results for different reactor configurations and different system parameters show that the distribution pattern of θ developed in the catalyst pellets during the multi-pulse experiment is fixed by the Thiele modulus or effectiveness factor of fresh catalyst in the first pulse experiment. Distribution patterns showing very steep profiles of θ for small effectiveness factors indicate that intraparticle non-uniformity of change in catalyst activity should be concerned when interpreting TAP response data during the multi-pulse experiment. Calculation examples showing the effect of the non-uniformity on the response data are provided.