Morphology and CO adsorption on platinum supported on thin Fe3O4(111) films

Nucleation, growth and thermal stability of Pt particles supported on well ordered Fe3O4(111) thin films grown on Pt(111) were studied by scanning tunnelling microscopy (STM) and temperature programmed desorption (TPD) of CO. STM studies showed that Pt grows through the formation of single-layer islands that coalesce at high coverage. Vacuum annealing at 600 K caused Pt sintering and the formation of extended two-dimensional (2D) islands one and two layers in thickness at sub-monolayer coverage. Well faceted, three-dimensional (3D) Pt nanoparticles formed by annealing to temperatures above 800 K were encapsulated by an FeO(111) monolayer. These results were rationalized in terms of the high adhesion energy for Pt on iron oxide surfaces. CO TPD studies showed that 2D structures, formed at 600 K, exhibit much lower CO adsorption capacity as compared to the Pt(111) single crystal surface. This effect has been tentatively assigned to lattice expansion in the Pt 2D islands leading to weakening of the Pt-CO bond due to reduction of the Pt -> CO pi* back-donation.