Cooperative catalytic nanokinetics

Abstract

• Theoretical framework for cooperative kinetics on nanoclusters with several adsorbed molecules. • Development of kinetic equations for common reaction mechanisms. • Analysis of selectivity in consecutive and parallel reactions. • Comparison of theory with experimental data on chemoselective hydrogenation. Cooperative kinetics of heterogeneous catalytic reactions on nanoclusters or in a nanoconfined space is considered for the Eley-Rideal and Langmuir-Hinshelwood types of mechanisms as well as for a reaction mechanism with two kinetically significant steps, by assuming few (minimum two) molecules of different type per a single metal cluster/catalytic ensemble. The treatment accounted for the lateral interactions between adsorbed species by introducing kinetic and adsorption constants dependence on the presence of adsorbed species of the same or another type. Kinetic behavior for the Eley-Rideal type of mechanism with the product adsorption was different from the classical mean –field approximation, resulting in S-shape behavior and cooperativity, while the Langmuir-Hinshelwood mechanism essentially gives the same behavior for the case of two adsorbed species of different type on a two-site ensemble. Differences in the kinetic behavior for the bimolecular mechanism compared to the conventional treatment could be seen for larger ensembles, when at least three species are adsorbed per cluster or located in a nanoconfined space. For parallel reactions of the Eley-Rideal type, it was demonstrated that the cooperative behavior of two adsorbed molecules of a reactant per cluster results in selectivity dependence on conversion for reactions of the same order contrary to the mean field approach. In the case of consecutive reactions with such cooperative behavior, selectivity towards the intermediate product depends on the initial substrate concentration in contrast to the mean field approximation.