Mechanisms of the various nitric oxide reduction reactions on a platinum-rhodium (100) alloy single crystal surface

H. Hirano, T. Yamada, K. I. Tanaka, J. Siera, P. Cobden, B. E. Nieuwenhuys

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80 Citations (Scopus)

Abstract

The reduction of nitric oxide with hydrogen was studied over a Pt0.25-Rh0.75(100) alloy surface used as a model catalyst for the automotive three-way catalyst. This paper emphasizes the mechanisms of the different reactions leading to the products dinitrogen, ammonia and nitrous oxide. For this purpose the reaction was studied under various experimental conditions including reactivity measurements both in the 10-7 mbar range under steady-state conditions and in the 10 mbar range with varying NO/H2 ratio. In addition, the thermal decomposition of NO and the reactions of NO + NH3 were investigated. 15NO and 15NH3 were used in order to gather additional information concerning the mechanisms of the formation reactions of the various N-containing products. The surface was characterized by using low-energy electron diffraction. Auger electron spectroscopy and thermal desorption spectroscopy. The main conclusions emerging from these studies are: (a) N2 can be formed by combination of 2 N adatoms in the whole temperature range used (350-1300 K) provided that sufficient N adatoms are available. (b) Below 600 K the main contribution to N2 formation is via NOads + Nads → N2+ Oads. At higher temperatures the dominant mechanism is 2Nads → N2. (c) N2O and NH3 are formed via Nads + NOads → N2O, and Nads + 3Hads → NH3 the contributions of which respectively decre increase with increasing temperature, (d) The selectivities to N2, NH3 and N2O are determined by the relative concentrations of NOads, Nads and Hads which vary with the experimental conditions such as the temperature.

Original languageEnglish
Pages (from-to)97-112
Number of pages16
JournalSurface Science
Volume262
Issue number1-2
DOIs
Publication statusPublished - 1992 Feb 1
Externally publishedYes

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Materials Chemistry

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