Dehydrogenation on alumina-supported size-selected Pt clusters: Fluxionality, metastable active sites, sintering and selectivity control via nanoalloying

Thermal dehydrogenation catalyzed by size-selected Pt clusters supported on alumina (a model catalyst) is studied by a combination of theory and experiment. We will show how catalytic clusters exist as dynamic ensembles of diverse structures, each featuring unique activity and selectivity, and creating a swarm of coexisting catalytic mechanisms. We model such catalysts as statistical ensembles, which, in thermodynamic limit, majorly change concurrently with the catalyzed reaction, effectively taking part in the reaction coordinate. We explicitly probe the thermodynamic limit via theory, and show that kinetic trapping while possible is rare. Metastable states may dominate the activity and define the selectivity. Metastable states also play a key role in the catalyst degradation, opening new pathways for sintering and poisoning. Via theory and experiment, we demonstrate that cluster can have “magic numbers” of sintering resistance. We will also show how coking on these clusters can be suppressed by alloying, and how the synergy between the dopant and the poison (carbon) leads to a creation of ultra-stable and selective cluster catalyst – potentially a new route to cluster catalyst stabilization.