Bi-metallic clusters have unique catalytic properties, since one metal can modify the electronic and thus the catalytic properties of the other metal. Here we describe a unique preparation method of bimetallic Pd-Au nano-clusters. The growth mode is based on initial evaporation of metal atoms on top of amorphous solid water adsorbed on SiO₂/Si(100) substrate at 100K under ultra high vacuum (UHV) conditions. The ice buffer layer separates the small metallic seed clusters from the substrate. Subsequent annealing to 300K desorbs the water molecules, resulting in aggregation and growth of nano-clusters in a Buffer Layer Assisted Growth (BLAG) mechanism.

Transmission Electron Microscope (TEM), Energy Dispersive X-ray (EDX) and X-Ray Diffraction (XRD) measurements revealed that by modifying the clusters preparation procedure either segregated or alloyed Pd-Au clusters can be formed. The composition of the different clusters was also verified by optical surface plasmon resonance (SPR) absorption measurements.

Temperature Programmed Reaction (TPR) measurements have shown that adsorption of acetylene on top of Pd-Au alloy clusters has led to efficient conversion to ethylene. Benzene was also formed at an order of magnitude smaller rate. Pd-Au alloy clusters have demonstrated significantly higher reactivity than the monometallic clusters. Increasing the surface defects density by Ar⁺ ion sputtering enhanced the thermal stability and sintering resistance properties of the Pd-Au clusters.