The structure and reactivity of anchored nanoparticles on a reducible support

Abstract

We have used scanning tunnelling microscopy (STM) to study the structure and reactivity of metal nanoparticles on a TiO₂(110) surface. We have deposited two metals (Pt and Ru) using different techniques, metal vapour deposition (MVD) for Pt and metal organic chemical vapour deposition (MOCVD) for Ru. Pt was deposited onto a (1 × 3) reconstructed surface and is found to sinter at temperatures above 873 K, where the onset of nanoparticle mobility is expected. The effect that Pt has on the rate of re-oxidation of a more reduced titania sample with a (1 × 1) terminated surface was studied. At 673 K no preferential re-growth around the particles is observed and this has been attributed to the desorption characteristics of oxygen from Pt surfaces. The results are compared to those obtained from Pd covered TiO₂ where such preferential growth has previously been observed. Ru was deposited using a carbonyl precursor, Ru₃(CO)₁₂, and is found to adsorb preferentially on the (1 × 2) rows of a surface consisting of both (1 × 1) and (1 × 2) added row structures. Upon annealing the compound is initially de-carbonylated to leave Ru nanoparticles on the surface, which can then sinter with increasing temperature. These particles have been alloyed with Pt and their re-oxidation characteristics studied. The alloy particles alter the oxygen desorption characteristics from that of the constituent elements (Pt and Ru) and consequently an enhancement in the rate of re-oxidation of a TiO₂(110) surface at 673 K is observed.