Initial Interaction of Pd with MgO(100) Films

Growth and electronic structure of Pd on MgO(100) films, prepared on Mo(100) single crystal, were studied in situ under ultrahigh vacuum conditions by using ultraviolet photoelectron spectroscopy, Auger electron spectroscopy, high resolution electron energy loss spectroscopy, and low-energy electron diffraction. On the basis of valence band analysis, the Pd particles are of nonmetallic character at submonolayer-equivalent coverages. An interaction between the Pd particles and the MgO films has been observed, which may play a key role in chemisorption and catalysis. At higher coverages, the Pd epitaxially grows as (100) orientation. Thermal stability of the Pd particles depends on the coverage. Our experimental results agree with theory and suggest that surface oxygen vacancies on the MgO are active sites to bind the Pd particles. The presence of the properties of the nonmetallic particles is essential in catalytic reactions.