Mechanism of ammonia formation on Rh(111) studied by dispersive near-edge X-ray absorption fine structure spectroscopy

Masanari Nagasaka, Hiroshi Kondoh, Kenta Amemiya, Ikuyo Nakai, Toru Shimada, Reona Yokota, Toshiaki Ohta

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Abstract

The reaction mechanism of ammonia formation on a Rh(111) surface was investigated by means of dispersive near-edge X-ray absorption fine structure (dispersive-NEXAFS) spectroscopy. Nitrogen-covered Rh(111) surfaces were exposed to gaseous hydrogen (1.0-5.0 × 10-7 Torr) at constant surface temperatures (330-390 K) to form ammonia which desorbs immediately from the surface. Continuous data acquisition of nitrogen K-edge NEXAFS spectra enables us to monitor coverage changes of surface species during the progress of the reaction. The obtained NEXAFS spectra were well reproduced by summation of the standard spectra for N and NH. We found that the NH species, which is considered as a stable intermediate, is not only hydrogenised to NH3, but also decomposed into N and H under H2-lacking conditions. The reaction-order analyses indicate that the NH decomposition occurs at periphery of 2-dimensional islands of NH while the NH3 formation takes place most likely over the entire NH islands. We propose a two-step reaction mechanism: (1) formation of NH islands and (2) hydrogenation of the NH species to NH3. The former process reaches equilibrium with decomposition after a short period.

Original languageEnglish
Pages (from-to)2164-2170
Number of pages7
JournalJournal of Physical Chemistry C
Volume114
Issue number5
DOIs
Publication statusPublished - 2010 Feb 11

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ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

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