Effects of different gases on the morphology of Ir nanoparticles supported on the TiO2(110)-(1 x 2) surface

The preparation of Zr nanoparticles supported on the TiO2(110)-(1x2) surface and the effects of annealing in different gases were studied by scanning tunneling microscopy. The smallest Ir particles, measuring 1 nm and consisting of 8-10 atoms, were produced by the deposition of approximately 0.005 monolayer (ML) of Ir at 300 K. On an increase of the Ir coverage, the diameter of the particles gradually rose to 5 nm at 2 ML coverage. Annealing of the Ir-covered surfaces caused only slight changes below 700 K but led to migration and coalescence of the particles above 700 K. The hexagonal appearance of the larger particles suggested the formation of Ir crystallites with their (111) faces parallel to the plane of the support. The orientation of the slightly elongated particles was adjusted to the [001] direction of the TiO2(110)-(1 x 2) surface. In the presence of CO (10(-3) mbar), the smallest Ir particles (consisting of 8-10 atoms) disrupted into atomically dispersed Ir within a few minutes at 300 K. On an increase of the particle size, the disintegration proceeded more slowly, even at higher CO pressure. For particles larger than 3-4 nm, only minor corrosion of the nanoclusters was observed, even in the presence of 10 mbar CO. At higher temperature (600 K), the reversed process, the GO-induced agglomeration of small Ir particles, occurred. The adsorption of NO and O-2 also caused disruption of the Ir nanoparticles at 300-500 K. Such an effect was not experienced in the presence of N-2, which interacts only weakly with Ir-x crystallites.