Pt nanoparticles grown on fully oxidized and partially reduced CeO x (111) thin films have been studied by scanning tunneling microscopy and X-ray photoelectron spectroscopy to understand the effect of redox properties and nanostructures of ceria supports on the growth of Pt. Deposition of 0.2 ML of Pt on CeO2 at 300 K produces two atomic layer high nanoparticles, while on reduced ceria films Pt favors the growth of smaller particles of one−two layer thick with a larger particle density. With the increase of Pt coverage, Pt particles on CeO2 grow in size while the Pt particle density significantly increases on the reduced ceria. Heating the surface to higher temperatures causes the Pt particle agglomeration, but Pt particles sinter less on the reduced ceria compared to those on the fully oxidized ceria. New particle structures are formed on reduced ceria as a result of heating which are suggested due to the encapsulation of Pt particles by ceria. In addition to the structural changes of the Pt particles, modifications of electronic properties of both ceria and Pt were observed upon Pt deposition as well as after heating. Our combined scanning tunneling microscopy and X-ray photoelectron spectroscopy studies suggest a complex growth behavior of Pt on ceria and a strong interaction between the Pt and the ceria support.

The effect of nanostructures of ceria associated with oxygen vacancies as well as Ti dopant on the structure of Ni was investigated by adopting model Ni/ceria systems consisting of Ni nanoparticles supported on well-ordered CeO x -(111) (1.5 < x < 2) thin films with/without Ti dopant using scanning tunneling microscopy under ultrahigh vacuum conditions. The surface defects related with oxygen vacancies on the reduced ceria act as the nucleation sites for Ni, which causes the formation of Ni particles with a smaller size and a higher particle density compared to those on CeO 2 at 300 K. Ni experiences a significant particle aggregation on pure ceria surfaces upon heating to higher temperatures, although slightly less Ni sintering was observed on the reduced ceria. Doping ceria with Ti element can help prevent the Ni sintering and stabilize the Ni particles on the surface upon heating, making it an attractive support for practical Ni catalysts with high stability.