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 Pt4 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 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 C2 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.