Stabilization of Nanoparticles Produced by Hydrogenation of Palladium–N-Heterocyclic Carbene Complexes on the Surface of Graphene and Implications in Catalysis

Palladium nanoparticles (NPs) have
been obtained by decomposition
of well-defined palladium complexes noncovalently anchored onto the
surface of reduced graphene oxide. Morphological analysis by microscopy
showed the presence of small palladium NPs homogeneously distributed
on the support. Characterization by X-ray photoelectron spectroscopy
confirmed that palladium NPs contain Pd­(2+) and Pd(0) oxidation states
and the presence of N-heterocyclic carbene and bromo ligands. The
catalytic properties of the NPs with and without the support have
been evaluated in the hydrogenation of alkynes. Supported palladium
NPs showed increased activity versus the nonsupported ones and could
be recycled up to 10 times without the loss of catalytic activity.
The composition of the palladium NPs is different for each catalytic
cycle indicating a dynamic process and the formation of different
catalytic active species. On the contrary, the unsupported palladium
NPs showed limited activity caused by decomposition and could not
be recycled. The role of the support has been investigated. The results
indicate that the support influences the stability of palladium NPs.