Development of a Master Equation-Based Microkinetic Model to Investigate Gas Phase Cluster Reactions Across a Wide Pressure and Temperature Range.

Small gas-phase metal clusters serve as model systems for complex catalytic reactions, enabling the exploration of the impacts of the size, doping, charge state and other factors under clean conditions. Although the mechanisms of reactions involving metal clusters are known in many cases, they are not always sufficient to interpret the experimental results, as those can be strongly influenced by the chemical kinetics under specific conditions. Therefore, our objective here is to develop a model that utilizes quantum chemical computations to comprehend and predict the precise kinetics of gas-phase cluster reactions, particularly under low-pressure conditions. In this study, we demonstrate that master equation simulations, utilizing reaction paths computed through quantum chemistry, can effectively elucidate the findings of previous experiments. Furthermore, these simulations can accurately predict the kinetics spanning from low-pressure conditions (typically observed in gas-phase cluster experiments) to atmospheric or higher pressures (typical for catalytic experiments). The models are tested for simple elementary steps (Cu₄+H₂). We highlight the importance of the reaction mechanism simplification in Cu₄ ⁺+H₂ and provide an interpretation for the previously observed product branching in Pt⁺+CH₄.