Fe/SSZ-13 as an NH3-SCR Catalyst: A Reaction Kinetics and FTIR/Mössbauer Spectroscopic Study
Abstract
Using a traditional aqueous solution ion-exchange method under a protecting atmosphere of N2, an Fe/SSZ-13 catalyst active in NH3-SCR was synthesized. Mössbauer and FTIR spectroscopies were used to probe the nature of the Fe sites. In the fresh sample, the majority of Fe species are extra-framework cations. The likely monomeric and dimeric ferric ions in hydrated form are [Fe(OH)2]+ and [HO-Fe-O-Fe-OH]2+, based on Mössbauer measurements. During the severe hydrothermal aging (HTA) applied in this study, a majority of cationic Fe species convert to FeAlOx and clustered FeOx species, accompanied by severe dealumination of the SSZ-13 framework. The clustered FeOx species do not give a sextet Mössbauer spectrum, indicating that these are highly disordered. However, some Fe species in cationic positions remain after aging as determined from Mössbauer measurements and CO/NO FTIR titrations. NO/NH3 oxidation reaction tests reveal that dehydrated cationic Fe are substantially more active in catalyzing oxidation reactions than the hydrated ones. For NH3-SCR, enhancement of NO oxidation under ‘dry’ conditions promotes SCR rates below ~300 • C. This is due mainly to contribution from the “fast” SCR channel. Above ~300 • C, enhancement of NH3 oxidation under ‘dry’ conditions, however, becomes detrimental to NOx conversions. The HTA samplemore »
- Authors:
- Publication Date:
- Research Org.:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Org.:
- USDOE
- OSTI Identifier:
- 1167593
- Report Number(s):
- PNNL-SA-104426
Journal ID: ISSN 0926-3373; 47953; VT0401000
- DOE Contract Number:
- AC05-76RL01830
- Resource Type:
- Journal Article
- Journal Name:
- Applied Catalysis. B, Environmental
- Additional Journal Information:
- Journal Volume: 164; Journal ID: ISSN 0926-3373
- Publisher:
- Elsevier
- Country of Publication:
- United States
- Language:
- English
- Subject:
- Selective catalytic reduction; chabazite; SSZ-13; Fe/SSZ-13; diesel engine; emission control; NOx; CO; FTIR; Mössbauer spectroscopy; Environmental Molecular Sciences Laboratory
Citation Formats
Gao, Feng, Kollar, Marton, Kukkadapu, Ravi K., Washton, Nancy M., Wang, Yilin, Szanyi, Janos, and Peden, Charles H.F. Fe/SSZ-13 as an NH3-SCR Catalyst: A Reaction Kinetics and FTIR/Mössbauer Spectroscopic Study. United States: N. p., 2015.
Web. doi:10.1016/j.apcatb.2014.09.031.
Gao, Feng, Kollar, Marton, Kukkadapu, Ravi K., Washton, Nancy M., Wang, Yilin, Szanyi, Janos, & Peden, Charles H.F. Fe/SSZ-13 as an NH3-SCR Catalyst: A Reaction Kinetics and FTIR/Mössbauer Spectroscopic Study. United States. https://doi.org/10.1016/j.apcatb.2014.09.031
Gao, Feng, Kollar, Marton, Kukkadapu, Ravi K., Washton, Nancy M., Wang, Yilin, Szanyi, Janos, and Peden, Charles H.F. 2015.
"Fe/SSZ-13 as an NH3-SCR Catalyst: A Reaction Kinetics and FTIR/Mössbauer Spectroscopic Study". United States. https://doi.org/10.1016/j.apcatb.2014.09.031.
@article{osti_1167593,
title = {Fe/SSZ-13 as an NH3-SCR Catalyst: A Reaction Kinetics and FTIR/Mössbauer Spectroscopic Study},
author = {Gao, Feng and Kollar, Marton and Kukkadapu, Ravi K. and Washton, Nancy M. and Wang, Yilin and Szanyi, Janos and Peden, Charles H.F.},
abstractNote = {Using a traditional aqueous solution ion-exchange method under a protecting atmosphere of N2, an Fe/SSZ-13 catalyst active in NH3-SCR was synthesized. Mössbauer and FTIR spectroscopies were used to probe the nature of the Fe sites. In the fresh sample, the majority of Fe species are extra-framework cations. The likely monomeric and dimeric ferric ions in hydrated form are [Fe(OH)2]+ and [HO-Fe-O-Fe-OH]2+, based on Mössbauer measurements. During the severe hydrothermal aging (HTA) applied in this study, a majority of cationic Fe species convert to FeAlOx and clustered FeOx species, accompanied by severe dealumination of the SSZ-13 framework. The clustered FeOx species do not give a sextet Mössbauer spectrum, indicating that these are highly disordered. However, some Fe species in cationic positions remain after aging as determined from Mössbauer measurements and CO/NO FTIR titrations. NO/NH3 oxidation reaction tests reveal that dehydrated cationic Fe are substantially more active in catalyzing oxidation reactions than the hydrated ones. For NH3-SCR, enhancement of NO oxidation under ‘dry’ conditions promotes SCR rates below ~300 • C. This is due mainly to contribution from the “fast” SCR channel. Above ~300 • C, enhancement of NH3 oxidation under ‘dry’ conditions, however, becomes detrimental to NOx conversions. The HTA sample loses much of the SCR activity below ~300 • C; however, above ~400 • C much of the activity remains. This may suggest that the FeAlOx and FeOx species become active at such elevated temperatures. Alternatively, the high-temperature activity may be maintained by the remaining extra-framework cationic species. For potential practical applications, Fe/SSZ-13 may be used as a co-catalyst for Cu/CHA as integral aftertreatment SCR catalysts on the basis of the stable high temperature activity after hydrothermal aging. The authors gratefully acknowledge the US Department of Energy (DOE), Energy Efficiency and Renewable Energy, Vehicle Technologies Office for the support of this work. The research described in this paper was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle.},
doi = {10.1016/j.apcatb.2014.09.031},
url = {https://www.osti.gov/biblio/1167593},
journal = {Applied Catalysis. B, Environmental},
issn = {0926-3373},
number = ,
volume = 164,
place = {United States},
year = {Sun Mar 01 00:00:00 EST 2015},
month = {Sun Mar 01 00:00:00 EST 2015}
}