CO adsorption on oxide supported gold: from small clusters to monolayer islands and three-dimensional nanoparticles

CO adsorption on gold vapor-deposited on a thin FeO(1 1 1) film grown on a Pt(1 1 1) has been studied with temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS). Structural characterization has been performed with scanning tunneling microscopy. Both TPD and IRAS results clearly show a particle size effect such that small Au deposits adsorb CO more strongly. This effect is only observed at low temperature deposition and vanishes after annealing to 500 K. However, the interaction of CO with Au monolayer islands, formed at a low Au coverage, and relatively large three-dimensional particles, formed at higher coverages, is found to be essentially similar. It is proposed that the adsorption of CO only involves low coordinated atoms and is consequently independent of the particles dimensions. The particle size effects are therefore attributed not to quantum size effects but rather to the presence of highly uncoordinated gold atoms in very small particles.