Promoter-poison partnership protects platinum performance in coked cluster catalysts

Abstract

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 exper- imental selectivity and stability of subnano Pt 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 Pt4 and Pt4C2 with and 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 C2 atoms. This prevents the coke from drawing electrons from the Pt, which is the origin of deactivation via coking. 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 sub-ensembles of isomers, where the dominant active sites are determined by kinetic stability under reaction conditions, rather than Boltzmann populations.