Reduction by Hydrogen of Oxidized Surfaces of Fe(100) and Pt-Covered Fe(100)

Abstract

The reduction at 555 K of oxidized Pt/Fe(100) surfaces by H2 has been studied using ellipsometry and Auger electron spectroscopy in combination with Ar+ ion bombardment. The surfaces considered here were first covered with Pt (0−1.1 monolayer) and then oxidized up to different oxygen uptakes. It is found that the initial rate at which the oxygen is removed by the hydrogen strongly decreases with oxide thickness and with initial Pt coverage. If the oxygen uptake exceeds 7 × 1015 atoms/cm2, the surfaces cannot be reduced. After deposition of about 0.5 monolayer Pt on top of such an oxide layer, exposure to H2 results in a reduction at the same rate as far thin oxide layers. It is concluded that the oxide can only be reduced if metallic atoms are available at the surface.