Anchoring of Ru-Pt and Ru-Au Clusters onto a Phosphane-Functionalized Carbon Support

Two mixed-metal clusters, [Ru5PtC(CO)(14)(COD)] (1) and [Ru6Au2C(CO)(16)(PPh3)(2)] (2), were anchored onto a prefunctionalized active carbon support (C-PPh2) with chelating phosphane groups on its surface. These clusters were also deposited onto the unmodified support (CSX+) for comparison. The incorporation of 1 and 2 on both supports was studied by a combination of SIMS and XPS. When the clusters were anchored onto the functionalized carbon support, SIMS spectra displayed characteristic patterns that were different from those obtained in the case of their deposition on the unmodified support. In the latter case, spectra corresponded to the results obtained with pure unsupported clusters. XPS analyses of the supported species seemed to indicate that the stoichiometry of the clusters was retained after anchoring and that their dispersion was better on C-PPh2 than on CSX+. This indicates that the phosphanes act as anchors for noble metal compounds through a ligand exchange mechanism. The supported samples were then thermally activated and characterized by SIMS, XPS, TEM/EDXS and XRD. Analyses by SIMS showed that the cluster ligand shell was removed during thermal treatment. XPS measurements indicated that the composition of the supported particles corresponded to that of the starting clusters and that the dispersion remained higher in the case of C-PPh2. Well-dispersed bimetallic-supported nanoparticles (1-2 nm) were obtained when cluster 1 was used as the precursor, whereas anchoring of cluster 2 resulted in its fragmentation leading to supported nanoparticles of variable stoichiometries. Reactions with soluble model molecules were carried out to prove the chemical bonding of 1. Crystallization of the new cluster [Ru5PtC-(CO)(14){(PPh2CH2)(2)NC3H7}] confirmed the chemical bonding of cluster 1 onto the C-PPh2 support through a ligand exchange mechanism involving COD.