Coupling the Diffusive Transport and Langmuir–Hinshelwood Reaction Kinetics for Kinetic Model Discrimination: A New Insight from an Old Concept

The overall rate of a heterogeneous catalytic process may be limited by the rate of a chemical transformation on the catalyst surface, reactant transport to either external or internal catalyst surface, or by the interplay between these factors. In this paper, we consider each case concerning the influence of diffusion limitations on the overall process rate. The internal, external, and overall effectiveness factors are obtained for various Langmuir-Hinshelwood kinetic rate equations and catalyst shapes via numerical simulations. It is shown that different kinetic rate equations provide an equally good description of the experimental data obtained under reaction-rate control. In contrast, the internal, external, and overall effectiveness factors may obey dissimilar trends for various kinetic rate equations. The obtained findings are of practical interest since the external and internal diffusion limitations can be achieved by simply changing the feed flow rate in a chemical reactor, catalyst particle size, or temperature increase. Therefore, the presented simulations deliver an easy and comprehensive tool for kinetic model discrimination based on the comparison of the overall effectiveness factors derived in the frame of various rate equations with the experimental one. This result represents a new utilization of an old concept, which is the effectiveness factor, for the selection between the plausible kinetic models.