The MgO(111) versus MgO(100) supported Au ultrasmall particles as a model catalyst for carbon monoxide oxidation

Adsorption and reaction of carbon monoxide and oxygen on gold ultrasmall particles deposited on MgO(111) and MgO(100) films in ultra-high vacuum have been studied by surface sensitive spectroscopic and structural techniques. The 3 nm thick MgO(111) and MgO(100) films were formed on Mo(110) and Mo(100) supports, respectively, as templates to grow the corresponding oxide structures. It is found that, unlike MgO(100), and many other oxide surfaces, reported in the literature, the Au particles of and average size of c.a. 2-3 nm, deposited on MgO(111), acquire an effective positive charge as a result of charge transfer from the metal as an effect stabilizing the uncompensated dipolar moment of the polar substrate. Gold nanoparticles on both MgO(111) and MgO(100) are active model catalysts for carbon monoxide oxidation by oxygen, as revealed by temperature desorption studies. However the effect of MgO(111) support is markedly more pronounced due to stronger interaction of precursor CO and O2 induced by specific state of supported Au ultrasmall particles.