Got Coke? Self-Limiting Poisoning Makes an Ultra Stable and Selective Sub-nano Cluster Catalyst

Supported sub-nano clusters hold great promise as economical and highly active catalysts. However, they tend to deactivate rapidly by poisoning and sintering, impeding their widespread use. We find that self-limiting poisoning can stabilize and promote cluster catalysis, i.e., poisoning is not always detrimental, but can sometimes be exploited. Specifically, Pt-Ge alloy clusters supported on alumina undergo slow coking (carbon deposition) under conditions of thermal dehydrogenation, yet preserve strong binding sites. For the case of Pt4Ge/alumina, theory shows a number of thermally populated isomers, one of which catalyzes carbon deposition. Because the clusters are fluxional at high temperatures, this isomer acts as a gateway, slowly converting all the clusters to Pt4GeC2. The surprising result is that Pt4GeC2 is highly catalytically active and selective against further coking, i.e., coking produces functional, stable catalytic clusters. Ge and C2 have synergistic electronic effects, leading to efficient and highly selective catalytic dehydrogenation that stops at alkenes, and improving stability. Thus, under reaction conditions, the clusters develop into a robust catalyst, suggesting an approach to practicable cluster catalysis.