The encapsulation (decoration) of Rh nanoparticles supported on a TiO2(110) surface was studied by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). In the case of a stoichiometric and well-ordered TiO2(110)-(1 × 1) surface covered by 3 monolayers (ML) of rhodium, there is no indication for thermally induced decoration of the metal particles by the suboxide phase of titania in the temperature range 300−800 K in ultrahigh vacuum (UHV). The encapsulation can be induced, however, by a few minutes annealing in a H2 atmosphere of 10-4 mbar at 750 K. The islands of TiO x phase on the top of the rhodium particles were clearly detected by STM. In the case of specially grown giant Rh crystallites (diameter of 10−15 nm) annealing in H2 at 750 K results in dramatic morphological changes (corrosion or disruption) of the original nanoparticles accompanying the encapsulation process. Pretreatment of the stoichiometric TiO2(110)-(1 × 1) surface by Ar+ bombardment (creation of surface and subsurface Ti3+ states) and the postdeposition of Rh on it results in encapsulation of Rh particles after annealing in UHV (in the absence of hydrogen).

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Rhodium in nanosize (1-3 nm) was prepared by vapor deposition of Rh on a well-ordered TiO 2 (110)1 × 2 single crystal. The morphology and the sizes of Rh had been determined by scanning tunneling microscopy in ultrahigh vacuum. The adsorption of CO at 300 K induces the disruption of Rh crystallites as indicated by a drastic decrease in the size of Rh particles. At higher temperature it leads to the re-forming of the Rh cluster.