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 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 clusters to Pt4GeC2. The surprising result
is that Pt4GeC2 is highly catalytically active
and selective against further coking, that is, 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.