On the nature of the silver phases of Ag/Al2O3 catalysts for reactions involving nitric oxide

N. Bogdanchikova, F. C. Meunier, M. Avalos-Borja, J. P. Breen, A. Pestryakov

Research output: Contribution to journalArticle

148 Citations (Scopus)

Abstract

The nature of the silver phases of Ag/Al2O3 catalysts (prepared by silver nitrate impregnation followed by calcination) was investigated by X-ray diffractograms (XRD), transmission electron microscopy (TEM) and UV-VIS analyses and related to the activity of the corresponding materials for the oxidation of NO to NO2. The UV-VIS spectrum of the 1.2 wt.% Ag/Al2O3 exhibited essentially one band associated with Ag+ species and the NO2 yields measured over this material were negligible. A 10 wt.% Ag/Al2O3 material showed the presence of oxidic species of silver (as isolated Ag+ cations and silver aluminate), but the UV-VIS data also revealed the presence of some metallic silver. The activity for the NO oxidation to NO2 of this sample was moderate. The same 10% sample either reduced in H2 or used for the C3H6-selective catalytic reduction (SCR) of NO showed a significantly larger proportion of silver metallic phases and these samples displayed a high activity for the formation of NO2. These data show that the structure and nature of the silver phases of Ag/Al2O3 catalysts can markedly change under reaction feed containing only a fraction of reducing agent (i.e. 500 ppm of propene) in net oxidizing conditions (2.5% O2). The low activity for N2 formation during the C3H6-SCR of NO (reported in an earlier study) over the high loading sample can, therefore, be related to the presence of metallic silver, which is yet a good catalyst for NO oxidation to NO2. The reverse observations apply for the oxide species observed over the low loading sample, which is a good SCR catalyst but do not oxidize NO to NO2.

Original languageEnglish
Pages (from-to)287-297
Number of pages11
JournalApplied Catalysis B: Environmental
Volume36
Issue number4
DOIs
Publication statusPublished - 28 Mar 2002

Keywords

  • Alumina
  • NO
  • NO
  • Silver
  • TEM
  • UV-VIS
  • XRD

ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology
  • Environmental Chemistry

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