A high pressure X-ray photoelectron spectroscopy study of oxidation and reduction of Rh(100) and Rh nanoparticles

We have studied the oxidation and reduction of Rh(100) and SiO2 supported Rh particles using high pressure X-ray photoelectron spectroscopy. We show that the formation and reduction of Rh bulk oxide can be followed in situ in O-2 and CO pressures in the range of 0.1 Torr. In general, the oxidation/reduction processes are similar on Rh(100) and the nanoparticles, but there are significant differences in temperature dependence. Already at a sample temperature of 140 degrees C, the particles show clear signs of a thin bulk oxide, while an ultra-thin so-called surface oxide covers the single crystal at the same temperature. Both of these oxide films, however, hinder further oxidation, and a thick oxide is only found at a temperature of at least 300 degrees C, for both samples. The reduction, in contrast, starts at a higher temperature on the particles as compared to the single crystal, but once started the particles are completely reduced at lower temperatures. (C) 2014 Elsevier B.V. All rights reserved.