Paper SS2-TuM11
Buffer Layer Assisted Deposition of Pb-Au Bimetallic Nano-clusters: Characterization and Chemical Reactivity

Tuesday, November 10, 2009, 11:20 am, Room N

Control over size and density of metallic nano-particles on oxide surfaces is important for studying model heterogeneous catalysts.

We have deposited metallic clusters on model SiO2 / Si(100) support, assisted by amorphous solid water (ASW) as a buffer. One may control this way the average size and density of metallic clusters independently by changing the ASW layer thickness, metal dosage and then repeat the deposition process. Bimetallic Pd-Au clusters were prepared this way and characterized by IR spectroscopy, AFM, SEM and TEM measurements in order to determine their structural and crystalline nature.

Directly deposited pure Pd clusters, 5±2 nm diameter, were found reactive in acetylene trimerization to benzene. The buffer assisted Pd-Au bimetallic clusters in comparison, are at least three times more reactive than the pure Pd, in spite of having smaller surface density of Pd atoms. Acetylene hydrogenation to ethylene was also studied. This product is two orders of magnitude more probable than benzene. Once again the bimetallic alloy was significantly more reactive than the pure Pd. Clean gold clusters were totally inactive. Preliminary results reveal the effect of pre-annealing to temperature below 300K, suggesting strong sensitivity to sintering. The possibility of size dependent reactivity will be discussed.