Got Coke? Self-Limiting Poisoning Makes an Ultra Stable and Selective Sub-Nano Cluster Catalyst
Patricia Poths, Guangjing Li, Tsugunosuke Masubuchi, Harry W. T. Morgan, Zisheng Zhang, Anastassia N. Alexandrova, Scott L. Anderson
Abstract
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, that is, poisoning is not always detrimental but can sometimes be exploited. Specifically, Pt–Ge alloy clusters supported on alumina undergo slow and self-limiting coking (carbon deposition) under conditions of thermal dehydrogenation, modifying the cluster framework and electronic properties but preserving the Pt sites required for strong ethylene binding. For the case of Pt 4 Ge/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 clusters to Pt 4 GeC 2 . The surprising result is that Pt 4 GeC 2 is highly catalytically active and selective against further coking, that is, coking produces functional, stable catalytic clusters. Ge and C 2 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.