Extraction of rate constant distributions from heterogeneous chemical kinetics

Abstract

The measured rate of a chemical process is often the sum of a series of individual rate processes. This paper outlines a computational method for the extraction of the distribution of rate constants in such a situation from the experimentally derived total rate plot against time. The method is tested using artificially generated data from given rate constant distributions and then applied to rate data obtained from reactions occurring on heterogeneous catalysts, to determine the site activity distribution functions prevailing on these surfaces. It constitutes, therefore, a means of quantifying the surface heterogeneity of a catalyst towards a reaction. Essential to the method are rate data of precision obtained under carefully controlled conditions, a requirement which is admirably fulfilled by carrying out the reaction in a chromatographic column using stopped-flow chromatography to measure reaction rates.