Co cation effects on activity and stability of isolated Pd(II) cations in zeolite matrices for selective catalytic reduction of nitric oxide with methane

Masaru Ogura, Susumu Kage, Tomoko Shimojo, Junko Oba, Masayoshi Hayashi, Masahiko Matsukata, Eiichi Kikuchi

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Palladium ion-exchanged zeolites (ZSM-5, mordenite, ferrierite, Y, beta) were tested to evaluate catalytic activity for selective reduction of nitric oxide with methane (CH4-SCR) and stability in the presence of 10% water vapor at a relatively high temperature of 500°C. Deactivation of the catalytic activity was inevitable on Pd/HZSM-5 with a Si/Al ratio of 19.8 under the reaction conditions. When the Si/Al ratio decreased, the durability was slightly enhanced. Among the zeolites tested, palladium supported on mordenite showed stable NO conversions. The addition of cobalt effectively stabilized the activity of Pd-H-zeolites, particularly with the addition of 3.3 wt% cobalt onto Pd/HZSM-5, of which no deactivation was noticeable for at least 50 h. Isolated Pd2+ cations on HZSM-5 were the active and selective sites for CH4-SCR. The isolated Pd2+ cations could not be exchanged by Na+ cations in NaCl titration test after the addition of 3.3 wt% cobalt, while NH4NO3 titration revealed that the isolated Pd2+ existed in the sample. This means that Co2+ changes the ion-exchange property of the isolated Pd2+, leading to a much higher stability than Pd/HZSM-5 with regard to durability. The effect of Co2+ on the stability of the isolated Pd2+ cations and their sitings in zeolite cavities is discussed.

Original languageEnglish
Pages (from-to)75-84
Number of pages10
JournalJournal of Catalysis
Issue number1
Publication statusPublished - 2002 Jan 1



  • CH-SCR
  • Isolated Pd
  • NHNO titration
  • NaCl titration
  • Pd-Co/HZSM-5, ion-exchange property
  • Pd/HZSM-5
  • Stability

ASJC Scopus subject areas

  • Catalysis
  • Physical and Theoretical Chemistry

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