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An IR spectroscopy study of Co sites in zeolites CoZSM-5

Paper ID Volume ID Publish Year Pages File Format Full-Text
43444 45970 2007 10 PDF Available
Title
An IR spectroscopy study of Co sites in zeolites CoZSM-5
Abstract

We examined the status and properties of Co2+ and Co3+ in CoZSM-5 zeolites of various Si/Al and Co contents and activated under various conditions. CO, NO and pivalonitrile were used as probe molecules. Some information on the status of Co was also obtained by comparing the intensities of Si–OH–Al bands and the concentration of protonic sites measured with pyridine. IR studies showed that in zeolite with high concentrations of AlO4− (of low Si/Al) practically all Co takes the form of Co2+ exchange cations (CO band at 2204 cm−1). However, in zeolites with low AlO4− concentrations (of high Si/Al) most Co occurs in the form of CoO (CO band at 2179 cm−1) or “oxide-like clusters” (bands at 2184 and 2194 cm−1, respectively). Experiments with co-adsorption of pivalonitrile and CO prove that all cobalt species (both in exchange positions and in “oxide-like clusters”) are situated inside zeolitic channels. The spectra of NO revealed the presence of three kinds of Co3+ (NO bands 1940, 1955 and 1970 cm−1), presence of Co2+ mononitrosyls (NO band at 1850 cm−1) and of Co2+ dinitrosyls (NO bands at 1815 and 1895 cm−1). Experiments on the co-adsorption of NO and CO suggested that NO can be bonded to Co2+ in exchange cationic positions, in “oxide-like clusters” (characterized by CO bands at 2204 and 2194 cm−1), but it cannot interact with Co2+ in “oxide-like clusters” (CO band at 2184 cm−1) or bulk CoO (CO band at 2179 cm−1).

Graphical abstractWe examined the status and properties of Co2+ and Co3+ in CoZSM-5 zeolites of various Si/Al and Co contents and activated under various conditions. CO, NO and pivalonitrile were used as probe molecules. Some information on the status of Co was also obtained by comparing the intensities of Si–OH–Al bands and the concentration of protonic sites measured with pyridine. Figure presents the evidence of various kinds of Co species: exchange cations, and several kinds of oxide-like species.Figure optionsDownload full-size imageDownload as PowerPoint slide

Keywords
Zeolite CoZSM-5; IR spectroscopy; Nitrosyls
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An IR spectroscopy study of Co sites in zeolites CoZSM-5
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 330, 10 October 2007, Pages 33–42
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us