Variation of SMSI with the Au:Pd Ratio of Bimetallic Nanoparticles on TiO(110).

Au/Pd nanoparticles are important in a number of catalytic processes. Here we investigate the formation of Au-Pd bimetallic nanoparticles on TiO(110) and their susceptibility to encapsulation using scanning tunneling microscopy, as well as Auger spectroscopy and low energy electron diffraction. Sequentially depositing 5 MLE Pd and 1 MLE Au at 298 K followed by annealing to 573 K results in a bimetallic core and Pd shell, with TiO encapsulation on annealing to ~ 800 K. Further deposition of Au on the pinwheel type TiO layer results in a template-assisted nucleation of Au nanoclusters, while on the zigzag type TiO layer no preferential adsorption site of Au was observed. Increasing the Au:Pd ratio to 3 MLE Pd and 2 MLE Au results in nanoparticles that are enriched in Au at their surface, which exhibit a strong resistance towards encapsulation. Hence the degree of encapsulation of the nanoparticles during sintering can be controlled by tuning the Au:Pd ratio.