Mechanism of CO oxidation reaction on O-covered Pd(111) surfaces studied with fast x-ray photoelectron spectroscopy: Change of reaction path accompanying phase transition of O domains

摘要

We studied the mechanism of CO oxidation on O-precovered Pd(111) surfaces by means of fast x-ray photoelectron spectroscopy (XPS). The oxygen overlayer is compressed upon CO coadsorption from a p(2x2) structure into a (root 3x root 3)R30 degrees structure and then into a p(2x1) structure with increasing CO coverage. These three O phases exhibit distinctly different reactivities. (1) The p(2x2) phase does not react with CO unless the surface temperature is sufficiently high (< 290 K). (2) In the (root 3x root 3)R30 degrees phase, the reaction occurs exclusively at island peripheries. CO molecules in a high-density phase formed under CO exposure react with oxygen atoms, leading to quite a small apparent activation energy. (3) The reaction proceeds uniformly over the islands in the p(2x1) phase. (c) 2006 American Institute of Physics.