Charge polarization at catalytic metal-support junctions : Part A : Kelvin probe force microscopy results of noble metal nanoparticles

Abstract

Metal oxide-supported nanoparticles of the platinum group metals Pt, Rh and Pd were studied at ambient temperature and atmosphere using Kelvin probe force microscopy. In all cases, the results reveal electron transfer from the metal to the oxide support which decreases in the order TiO2 > CeO2 >> Al2O3, leading to charge polarization at the Schottky type interfaces analogous to that of a parallel plane capacitor. This polarization cancels out to a large extent for the Kelvin signal. On top of this there is a much smaller number of positive charges at the outer catalyst particle surface, compensated by negative charges near the oxide surface. They show the same trend over the different oxides. These charges determine the constant electrical potential of the metal and are suggested to be the important component of the electronic catalytic metal-support interaction which are known to be much stronger for reducible than for non-reducible oxides.