Encapsulation of Pt Nanoparticles as a Result of Strong Metal−Support Interaction with Fe3O4 (111)

The morphology and thermal stability of Pt particles deposited on Fe3O4 (111) films were studied by scanning tunneling microscopy (STM) and temperature programmed desorption of CO. Vacuum annealing at temperatures above 800 K led to significant Pt sintering that reduced CO uptake to a much higher extent than the Pt surface area. A similar effect on CO adsorption was observed after mild oxidation−reduction treatment at 500 K. The results are rationalized in terms of the strong metal−support interaction between Pt and Fe3O4, whereby the Pt particles were encapsulated by a FeO (111) monolayer film as shown by STM. The high adhesion energy between Pt and iron oxides derived from STM data is suggested to be the key factor for encapsulation.