In Situ Photoemission Observation of Catalytic CO Oxidation Reaction on Pd(110) under Near-Ambient Pressure Conditions: Evidence for the Langmuir-Hinshelwood Mechanism

CO oxidation reaction on a Pd(110) single crystal surface at various temperatures under near-ambient-pressure conditions has been investigated using in situ X-ray photoemission spectroscopy and mass spectroscopy. At lower temperature conditions, the CO2 formation rate is low, where the surface is covered by CO molecules (i.e., CO poisoning). Above a critical temperature 165 degrees C the Pd(110) surface converts to a catalytically active surface and is dominated by chemisorbed oxygen species. Further at the higher temperatures up to 320 degrees C, the CO2 formation rate is gradually decreased to about 80% of the maximum rate. At this moment, the amount of chemisorbed O was also decreased, which suggests that the CO oxidation reaction proceeds via the conventional Langmuir-Hinshelwood mechanism even under near-ambient pressure conditions.