Formation of Epitaxial PdO(100) During the Oxidation of Pd(100)

The catalytic oxidation of CO and CH4 can be strongly influenced by the structures of oxide phases that form on metallic catalysts during reaction. Here, we show that an epitaxial PdO(100) structure forms at temperatures above 600 K during the oxidation of Pd(100) by gaseous O atoms as well as exposure to O-2-rich mixtures at millibar partial pressures. The oxidation of Pd(100) by gaseous O atoms preferentially generates an epitaxial, multilayer PdO(101) structure at 500 K, but initiating Pd(100) oxidation above 600 K causes an epitaxial PdO(100) structure to grow concurrently with PdO(101) and produces a thicker and rougher oxide. We present evidence that this change in the oxidation behavior is caused by a temperature-induced change in the stability of small PdO domains that initiate oxidation. Our discovery of the epitaxial PdO(100) structure may be significant for developing relationships among oxide structure, catalytic activity, and reaction conditions for applications of oxidation catalysis.

Automated summary

The structures of oxide phases on metallic catalysts during reaction have a strong influence on the catalytic oxidation of CO and CH4. It has been found that an epitaxial PdO(100) structure forms on Pd(100) at temperatures above 600 K during the oxidation process. Additionally, the oxidation behavior of Pd(100) changes from forming epitaxial PdO(101) at 500 K to simultaneously growing epitaxial PdO(100) and PdO(101) at temperatures above 600 K, resulting in a thicker and rougher oxide layer. This change is attributed to a temperature-induced change in the stability of small PdO domains that initiate the oxidation process.