Promoter-Poison Partnership Protects Platinum Performance in Coked Cluster Catalysts

Deactivation via coking due to a lack of selectivity is a persistent problem for the longevity of Pt-based dehydrogenation catalysts. Ge as a promoter improves the experimental selectivity and stability of subnano Pt-4 clusters. The origin of this improvement is self-limiting coking to form a Pt4GeC2 cluster which is more stable and selective than the bare Pt4Ge cluster. In this paper, we compare the dehydrogenation abilities of Pt-4 and Pt4C2 and of Pt4Ge and Pt4GeC2 with DFT calculations in order to explore the origin of self-limiting coking in the presence of Ge. The unique stability of Pt4GeC2 is attributed to electron donation from Ge to the C-2 atoms. This prevents the coke from drawing electrons from the Pt, which is the origin of deactivation via coking, and weakens ethylene binding. Thus, we identify an electronic mechanism for coke deactivation and then use an electronically driven doping strategy to improve catalyst longevity. This differs from the common perception of coke deactivating via steric blocking of active sites. Furthermore, Pt4C2 and Pt4GeC2 show differences in kinetic accessibility of different isomers, which brings us into a new paradigm of subensembles of isomers, where the dominant active sites are determined by kinetic stability under reaction conditions, rather than Boltzmann populations.