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Quantitative IR studies of the concentration of Co2+ and Co3+ sites in zeolites CoZSM-5 and CoFER

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Abstract
Quantitative IR experiments were realized to determine the concentration of cobalt in a form of trivalent
cations being in the oxide form as well as divalent ions in exchange positions, oxide-like clusters and
cobalt oxide, present in a series of cobalt-exchanged zeolites. The first step of such quantitative studies
was to elaborate the experimental conditions in which probe molecules NO and CO should react
selectively with either of these sites. Subsequently, the values of absorption coefficients of the 1940 cm1
band of Co3+–NO and the 2204 cm1 band of Co2+–CO for Co2+ in exchange positions, together with the
2194 cm1 band of Co2+–CO for Co2+ in oxide-like clusters were determined. The linear plots of the band
intensities versus the concentration of NO and CO interacting with cationic sites showed the correlation
coefficients higher than 0.99. Three zeolites were investigated: CoZSM-5 (Si/Al = 15) in which most of
Co2+ occupied the exchange positions, CoZSM-5 (Si/Al = 40) in which most of Co2+ was in the form of
oxide-like clusters and CoO, and CoFER prepared by the contact-induced ion exchange with nearly equal
amount of Co2+ in either type of the sites. The sum of the concentration of Co sites (Co3+ and Co2+)
determined by IR spectroscopy was very close to the values obtained from the chemical analysis (AAS).
The concentration ill-defined oxide form of Co3+ was surprisingly high as in CoZSM-5 of Si/Al = 15 it
constituted about half of the overall cobalt content, and in CoFER the contribution of Co3+ reached almost
30%.

Keywords:CoZSM-5, CoFER, IR spectroscopy, Absorption coefficient

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Informasi Detail

Judul Seri

Applied Catalysis A: General

No. Panggil

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Penerbit

London : Elsevier B.V.., 2009

Deskripsi Fisik

Applied Catalysis A: General 353 (2009) 117–122

Bahasa

English

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Klasifikasi

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Tipe Isi

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Tipe Media

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Tipe Pembawa

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Edisi

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Subjek

KIMIA

Info Detail Spesifik

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Pernyataan Tanggungjawab

agus

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