Interaction of NO with potassium promoted Pt(111)

Abstract

The interaction of NO with a K-covered Pt(111) surface was studied at various adsorption temperatures ranging from 120 to 570 K by means of XPS, UPS and AES and compared to NO adsorption on clean Pt(111). It was found that NO adsorption is preferentially molecular at potassium coverages θ K < 0.18 and T < 305 K. The NO species adsorbed on the K promoted surface are more tightly bound and possess a large negative charge as deduced from work function changes. They are characterized by an O(1s) peak at 531.0 eV which grows at the expense of the 532.5 and 530.6 eV O(1s) peaks associated with on top and bridge bonded NO molecules on a clean surface. Heating of the coadsorbed K NO layer to > 300 K leads to NO dissociation associated with a loss of surface nitrogen. The XPS and UPS spectra provide evidence for this dissociation and in addition for the formation of an NO 2 species with O(1s) and N(1s) peaks at 532.8 and 404.0 eV, respectively. The probability for the formation of K-promoted NO 2 increases with rising NO adsorption temperature and potassium coverage. This NO 2 species is negatively charged due to the enhanced electron donation into its 6a 1 molecular orbital; it starts to decompose at about 450 K.