Vibrational spectra of nitric oxide chemisorbed on Pt(100)

Abstract

The chemisorption of NO on a Pt(100) single crystal surface at 140 and 300 K was investigated by high resolution electron energy loss spectroscopy, combined with Auger electron spectroscopy and LEED. Chemisorption of NO was predominantly molecular. The unreconstructed Pt(100)−1×1 surface was characterized by a single NO stretch frequency at 1615 cm−1 and two low frequency vibrations at 230 and 380 cm−1. These latter modes are likely to represent the Pt–NO stretch and Pt–N–O bending vibrations, respectively. The adsorbed molecule has therefore Cs symmetry in this case and is bent with respect to the surface normal. Low coverage NO adsorption at 140 K on the reconstructed Pt(100)−5×20 surface gave rise to three frequencies at 1690, 465, and 310 cm−1. Thus NO is also adsorbed in a bent configuration on this surface. At higher coverage an additional NO stretch frequency at 1790 cm−1 indicated a second adsorption site. Low frequency modes could not be clearly resoled for this species. NO adsorption on the same surface at 300 K was characterized by frequencies at 1805, 1630, and 380 cm−1, independent of NO coverage. At this temperature the reconstruction of the surface is lifted locally where NO adsorption took place. In analogy to the 1×1 surface it was concluded that the major NO state corresponds to a bent NO molecule while the 1805 cm−1 frequency represents NO adsorbed on a defect site which is created by the structure transformation.

Evidence for an oxygen intermediate in the catalytic reduction of NO by CO on rhodium surfaces

“…The weak band at 403 cm 1 is characteristic of a metal-nitrogen bending mode for an associatively adsorbed species. 17 , 18 This is in agreement with the observation of a bent nitrosyl. The normal dipole selection rule 22 would not allow the observation of such a mode if the adsorbate was bonded perpendicular to the surface.…”

“…The normal dipole selection rule 22 would not allow the observation of such a mode if the adsorbate was bonded perpendicular to the surface. The metal-nitrogen stretching vibration from such a species is expected to be 00-200 " lower in frequency, The results of detailed infrared studies on numerous nttrosyl compounds have been reviewed recently by Pirug, etal, 18 They conclude that the experimental data on both the halogen nitrosyls and transition metal nitrosyls provide evidence for well separated M-N-0 bending and stretching frequencies with the latter always lower than the former.…”

Bridge-bonded adsorbates on fcc(100) and fcc(111) surfaces: A kinetic Monte Carlo study

“…This system has been studied by many authors, and it has been clear from LEED measurements that a c͑4 ϫ 2͒ structure is formed on the unreconstructed surface. 42,43 Vibrational studies indicated that NO is bound at one type of site. [43][44][45] Recent electronic structure calculations clearly indicate that this must be the bridge type site.…”

“…42,43 Vibrational studies indicated that NO is bound at one type of site. [43][44][45] Recent electronic structure calculations clearly indicate that this must be the bridge type site. 46,47 Up to now there has been one direct observation of this c͑4 ϫ 2͒ structure, by STM, and this clearly indicated a coverage of 0.25 ML.…”

The interaction of nitric oxide with platinum and platinum-silver catalysts

“…At high NO coverages, vibrational frequencies of 1710 cm for the (111) face [4,7], 1760 cm' for the (110) face [5] and 1790 cm' for the (100) face [19] have been established by EELS. Assuming an increasing fraction of (111) planes with increasing particle size, these data predict a shift to lower frequencies with larger particles.…”