Surface structure and reactivity of Pd(100) during CO oxidation near ambient pressures.

The surface structure of Pd(100) during CO oxidation was measured using a combination of a flow reactor and in situ surface X-ray diffraction coupled to a large-area 2-dimensional detector. The surface structure was measured for P(O(2))/P(CO) ratios between 0.6 and 10 at a fixed total gas pressure of 200 mbar and a fixed CO pressure of 10 ± 1 mbar. In conjunction with the surface structure the reactivity of the surface was also determined. For all P(O(2))/P(CO) ratios the surface was found to oxidize above a certain temperature. Three different types of oxides were observed: the surface oxide, an epitaxial layer of bulk-like PdO, and a non-epitaxial layer of bulk-like PdO. As soon as an oxide was present the reactivity of the surface was found to be mass transfer limited by the flux of CO molecules reaching the surface. This journal is © the Owner Societies 2011