Can Fluxionality of Subnanometer Cluster Catalysts Solely Cause Non-Arrhenius Behavior in Catalysis?

Supported subnanoclusters are intriguing catalysts, which can present an ensemble of many distinct and easily interconverting geometric states to the reactive medium in catalytic conditions. Each of these states can contribute to catalysis with a unique reaction rate. We argue that such subnanocluster catalysts can, in principle, show a non-Arrhenius behavior, thanks to their structural fluxionality. However, it is unlikely to see this in practice due to the stringent requirements on the heights of the reaction barriers involved. Furthermore, we demonstrate that the ensemble average rate constant which was previously proposed to be used for the ensemble of fluxional clusters to describe the catalytic properties of the system is the same as Tolman's formula proposed in 1920. Note that in this study we only isolate the dynamicity of clusters as one factor that can affect the kinetics of catalysis. We also propose that calculating 1/k(B)(< E-TS > - < E-R >) as a function of T can be used as a good indicator of a possible non-Arrhenius behavior.