CHEMISORPTION OF NO ON PT(210) STUDIED BY UPS, XPS AND AES

The chemisorption of NO on the Pt(210) surface has been studied by photoelectron spectroscopy (UPS and XPS) and Auger electron spectroscopy (AES). The UPS results show that NO molecular orbitals appear at 2.8, 9.6, 11.3 and 14.8 eV below the Fermi level after full coverage of NO on the Pt(210) surface at room temperature. These molecular orbitals originate from 2pi, 1pi, 5sigma and 4sigma, respectively. The peak from the 1pi orbital shifts to the lower binding energy side by 0.6 eV with increasing temperature. The molecular levels disappear at around 450 K. The energy shift of the 1pi orbital is caused by the increase of the N-O bond length, which correlates with the change of adsorption state of NO; that is, from the terminal sites to the bridge sites.The disappearance temperature of the NO molecular orbitals, T(D), and the decreasing temperature of the N(KLL) Auger electron intensity, T(A), correlate with the surface activity for NO decomposition. From the UPS and AES results for the Pt surfaces, the order of activity for the NO decomposition is as follows: (410) > (310) > (100) > (210) > (110).