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 degrees 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 degrees C), while at higher temperatures (300-400 degrees 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.This study was supported by the Grants-in-Aid for scientific research (No. 20245004) and the MEXT-Supported Program for the Strategic Research Foundation at Private Universities, 2009-2013. The experiments have been performed under the approval of the Photon Factory Program Advisory Committee (PF PAC No. 2010G151)