Surface science approach to catalyst preparation – Pd deposition onto thin Fe3O4(1 1 1) films from PdCl2 precursor

Abstract

In this work, we introduce a surface science approach to supported metal catalyst preparation utilizing thin, single-crystalline oxide films as substrates. The use of thin oxide films allows for combined morphological and chemical characterization of the sample at various steps of a typical catalyst preparation procedure. A Fe3O4-supported Pd model catalyst was prepared by impregnation of Fe3O4(111) films with acidic PdCl2 solution, and the transformation of the adsorbed precursor into supported Pd nanoparticles by stepwise heating in vacuum was followed with scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). The results provide evidence for homogeneous nucleation of Pd particles out of a monolayer of adsorbed precursor and an enhancement of the particle-support interaction with increasing annealing temperature. Chlorine, which remains on the model catalyst surface after vacuum annealing, could be removed by oxidation/reduction. This treatment also leads to particle sintering with an increase in the average particle diameter from 2nm to 4nm after oxidation/reduction.