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Title: Investigations of the state of Fe in H-ZSM-5

Abstract

The state of Fe dispersion in Fe-H-ZSM-5 was investigated by means of infrared spectroscopy of adsorbed NO, temperature-programmed desorption (TPD) of NO, TPD of NH{sub 3}, and H{sub 2} temperature-programmed reduction (TPR). For samples with a low loading of Fe [e.g., Fe/Al ratio {le} 0.56], Fe cations exchange with Broensted acid protons on a one-to-one basis, while at Fe/Al ratios above this level small particles of FeO{sub x} are formed. Results of H{sub 2} TPR and NO uptake experiments on Fe-ZSM-5 samples following a He pretreatment suggest that the primary form of Fe present on samples with an Fe/Al ratio less than or equal to 0.19 is Fe{sup 3+} [i.e., Fe{sup 3+} (OH{sup {minus}}){sub 2}]. An increase in the Fe loading above this level results in an increase in the concentration of Fe{sup 2+} cations formed via the autoreduction of Fe{sup 3+} (OH{sup {minus}}){sub 2} which is present at highly reducible {alpha} sites in ZSM-5. Three types of Fe{sup 2+} sites are observed on Fe-ZSM-5 during the room temperature adsorption of NO. They are defined as type I, II, and III sites. Type I sites adsorb NO as mononitrosyls (1767 cm{sup {minus}1}) and dinitrosyls (1917 and 1806 cm{sup {minus}1}). Typesmore » II and III sites adsorb NO solely as mononitrosyl species (1876 and 1856 cm{sup {minus}1}, respectively). While types II and III sites are found to be relatively resistant to oxidation and reduction, type I sites are significantly affected by these pretreatments. The most notable change occurs for the high-weight-loaded Fe-ZSM-5 sample in which CO reduction results in the redispersion of FeO{sub x} to type I sites.« less

Authors:
; ; ;  [1]
  1. Lawrence Berkeley National Lab., CA (United States). Chemical Sciences Div.|[Univ. of California, Berkeley, CA (United States). Dept. of Chemical Engineering
Publication Date:
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
687737
DOE Contract Number:  
AC03-76SF00098
Resource Type:
Journal Article
Journal Name:
Journal of Catalysis
Additional Journal Information:
Journal Volume: 186; Journal Issue: 2; Other Information: PBD: 10 Sep 1999
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 54 ENVIRONMENTAL SCIENCES; ZEOLITES; IRON; DISTRIBUTION; MOLECULAR STRUCTURE; PHASE STUDIES; NITRIC OXIDE; ADSORPTION; CATALYSTS; AIR POLLUTION CONTROL

Citation Formats

Lobree, L.J., Hwang, I.C., Reimer, J.A., and Bell, A.T. Investigations of the state of Fe in H-ZSM-5. United States: N. p., 1999. Web. doi:10.1006/jcat.1999.2548.
Lobree, L.J., Hwang, I.C., Reimer, J.A., & Bell, A.T. Investigations of the state of Fe in H-ZSM-5. United States. doi:10.1006/jcat.1999.2548.
Lobree, L.J., Hwang, I.C., Reimer, J.A., and Bell, A.T. Fri . "Investigations of the state of Fe in H-ZSM-5". United States. doi:10.1006/jcat.1999.2548.
@article{osti_687737,
title = {Investigations of the state of Fe in H-ZSM-5},
author = {Lobree, L.J. and Hwang, I.C. and Reimer, J.A. and Bell, A.T.},
abstractNote = {The state of Fe dispersion in Fe-H-ZSM-5 was investigated by means of infrared spectroscopy of adsorbed NO, temperature-programmed desorption (TPD) of NO, TPD of NH{sub 3}, and H{sub 2} temperature-programmed reduction (TPR). For samples with a low loading of Fe [e.g., Fe/Al ratio {le} 0.56], Fe cations exchange with Broensted acid protons on a one-to-one basis, while at Fe/Al ratios above this level small particles of FeO{sub x} are formed. Results of H{sub 2} TPR and NO uptake experiments on Fe-ZSM-5 samples following a He pretreatment suggest that the primary form of Fe present on samples with an Fe/Al ratio less than or equal to 0.19 is Fe{sup 3+} [i.e., Fe{sup 3+} (OH{sup {minus}}){sub 2}]. An increase in the Fe loading above this level results in an increase in the concentration of Fe{sup 2+} cations formed via the autoreduction of Fe{sup 3+} (OH{sup {minus}}){sub 2} which is present at highly reducible {alpha} sites in ZSM-5. Three types of Fe{sup 2+} sites are observed on Fe-ZSM-5 during the room temperature adsorption of NO. They are defined as type I, II, and III sites. Type I sites adsorb NO as mononitrosyls (1767 cm{sup {minus}1}) and dinitrosyls (1917 and 1806 cm{sup {minus}1}). Types II and III sites adsorb NO solely as mononitrosyl species (1876 and 1856 cm{sup {minus}1}, respectively). While types II and III sites are found to be relatively resistant to oxidation and reduction, type I sites are significantly affected by these pretreatments. The most notable change occurs for the high-weight-loaded Fe-ZSM-5 sample in which CO reduction results in the redispersion of FeO{sub x} to type I sites.},
doi = {10.1006/jcat.1999.2548},
journal = {Journal of Catalysis},
number = 2,
volume = 186,
place = {United States},
year = {1999},
month = {9}
}