In Situ Ambient Pressure XPS Study of CO Oxidation Reaction on Pd(111) Surfaces

The CO oxidation reaction on the Pd(111) model catalyst at various temperatures (200–400 °C) under hundreds mTorr pressure conditions has been monitored by in situ ambient pressure X-ray photoelectron spectroscopy and mass spectroscopy. In situ observation of the reaction revealed that the Pd(111) surface is covered by CO molecules at a lower temperature (200 °C), while at higher temperatures (300–400 °C) several oxide phases are formed on the surface. We found that the reactivity is enhanced in the presence of a surface oxide and significantly suppressed by formation of a cluster oxide and the PdO bulk oxide. CO titration experiments suggest that less coordinated oxygen atoms are more reactive for CO oxidation.