Carbon monoxide oxidation on epitaxial Cu(111)Pd(111) bilayers at atmospheric pressures

Abstract

Catalytic CO oxidation experiments on Pd(111) and on Cu-covered epitaxial Pd(111) thin film surfaces were carried out at atmospheric pressures. The films were formed in UHV and transferred to the attached high-pressure chamber with a bellow-sealed UHV transfer device, where reaction rates mere measured a with gas chromatogaph (GC). The surface temperature was held at 70°C during most of the reactions. An approximately 50% increase in the CO 2 formation rate over that on pure Pd(111) was observed for1/2 monolayer thick epitaxial Cu films formed on a Pd(111) surface. For the same Cu thickness and at 83°C the rate was ≈ 7 times more than the rate obtained on pure Pd(111). Another, but smaller, rate increase was observed at 3ML Cu. These two peaks in the catalytic oxidation reaction were interpreted in terms of models that involve changes in surface morphology during growth of the Cu overlayer.