Dynamic catalytic interfaces: ensembles of metastable states break the rules of catalysis

Professor Anastassia Alexandrova - UCLA (Host: Professor Wexler)

Abstract:

I will show that dynamic catalytic interfaces exhibit great structural fluxionality in conditions of catalysis. Catalysts populate many distinct structural and stoichiometric states, forming a constantly changing statistical ensemble, which can be off-equilibrium. Multitude of metastable states in this ensemble dictate the catalytic activity, selectivity, durability, and spectral characteristics. Many assumptions and rules in catalysis need a revision within this new paradigm. Firstly, catalyst dynamics is an essential part of the catalytic process. Scaling relations routinely break down. The most active catalyst state may not be the most stable (i.e. most dominant). On the other hand, operando spectra are overwhelmed by the signal form the most dominant species. High temperature phase diagrams contain many structures per phase, and get enthalpically destabilized but entropically stabilized by fluxionality, each phase to its own degree. The Ostwald theory of sintering needs a revision. 

These concepts will be presented using real catalysis examples, studied collaboratively with experiment, at times in a predictive mode. Showcase systems will include dehydrogenation on supported Pt catalysts, oxidative dehydrogenation of alkanes on supported Cu and CuPd oxide clusters, and ORR on supported Pt catalysts. I will also present a new challenge for theory: operando reconstruction of Cu electrodes in reduction conditions, illustrating the hard-to-grasp kinetic control. Some of our results will hopefully prompt experimental developments. For example, detecting dynamic minority active species of the catalytic interface remains a challenge.