Effect of Pt structure on the kinetics of NO oxidation as studied by Pt(321) and Pt(111) large single crystals and supported clusters from 2-9 nm

The kinetics of NO to NO₂ oxidation with O₂ on Pt was studied on the large single crystals Pt(321), Pt(111) and on clusters from 2-9 nm supported on alumina, silica, carbon and niobia. The rates on all samples were measured under the same conditions and thus the kinetics can be directly compared. Based on the kinetics, in situ XPS, in situ x-ray absorption, and environmental TEM we concluded that the reaction happens on a Pt surface covered with about 0.7 ML of oxygen and is independent of the underlying structure of the Pt except that smaller particles oxidize completely and become inactive. The complete oxidation of the Pt clusters is a strong function of particle size and explains the size dependence on the turnover rate. The turnover rate is constant for all samples when normalized to the amount of Pt that does not over-oxidize.