Variation of SMSI with the Au:Pd Ratio of Bimetallic Nanoparticles on TiO2(110)

Au/Pd nanoparticles are important in a number of catalytic processes. Here we investigate the formation of Au–Pd bimetallic nanoparticles on TiO2(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 TiOx encapsulation on annealing to ~ 800 K. Further deposition of Au on the pinwheel type TiOx layer results in a template-assisted nucleation of Au nanoclusters, while on the zigzag type TiOx 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.