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Title: New insights into Cu/SSZ-13 SCR catalyst acidity. Part I: Nature of acidic sites probed by NH 3 titration

Abstract

In this work we investigated an unusual acidity feature of a Cu/SSZ-13 catalyst used in selective catalytic reduction of NOx with NH3 (NH3-SCR). In particular, this catalyst showed two distinct NH3 desorption peaks in NH3-TPD measurements, in contrast to single, unresolved desorption peaks observed for other Cu-exchanged zeolites conventionally used in the SCR studies, including its isostructural but chemically different analogue Cu/SAPO-34. We further observed that the intensities of the two TPD peaks, which represented the amount of stored NH3, changed in opposite directions in response to progressive mild hydrothermal aging, while the total storage capacity was preserved. We proposed an explanation for this remarkable behavior, by using model reference samples and additional characterization techniques. At least three NH3 storage sites were identified: two distinct populations of Cu sites responsible for low-temperature NH3 storage, and Brønsted acid sites responsible for high-temperature NH3 storage. Contrary to the commonly accepted mechanism that Brønsted acid site loss during hydrothermal aging is driven by dealumination, we concluded that the decline in the number of Brønsted acid sites upon mild hydrothermal aging for Cu/SSZ-13 was not due to dealumination, but rather transformation of Cu sites, i.e., gradual conversion of ZCuOH (Cu2+ singly coordinated with Zeolite)more » to Z2Cu (Cu2+ doubly coordinated with Zeolite). This transformation was responsible for the increased low-temperature desorption peak in NH3-TPD since each ZCuOH adsorbed ~1 NH3 molecule while each Z2Cu adsorbed ~2 NH3 molecules under the conditions used here. These findings were used in Part II of this series of studies to develop a method for quantifying hydrothermal ageing of industrial Cu/SSZ-13 SCR catalysts. Authors would like to thank Randall Jines for his help with collecting the reactor data, Nancy W. Washton for measuring the NMR data and Tamas Varga for in-situ XRD measurements. FG and CHFP gratefully acknowledge supports from the United States Department of Energy (DOE), Energy Efficiency and Renewable Energy, Vehicle Technologies Office. Part of 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.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1347850
Report Number(s):
PNNL-SA-122484
Journal ID: ISSN 0021-9517; 47953; VT0401000
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Catalysis; Journal Volume: 348
Country of Publication:
United States
Language:
English
Subject:
zeolite; SCR; SSZ-13; NH3-TPD; hydrothermal aging; DRIFTS; Environmental Molecular Sciences Laboratory

Citation Formats

Luo, Jinyong, Gao, Feng, Kamasamudram, Krishna, Currier, Neal, Peden, Charles H. F., and Yezerets, Aleksey. New insights into Cu/SSZ-13 SCR catalyst acidity. Part I: Nature of acidic sites probed by NH 3 titration. United States: N. p., 2017. Web. doi:10.1016/j.jcat.2017.02.025.
Luo, Jinyong, Gao, Feng, Kamasamudram, Krishna, Currier, Neal, Peden, Charles H. F., & Yezerets, Aleksey. New insights into Cu/SSZ-13 SCR catalyst acidity. Part I: Nature of acidic sites probed by NH 3 titration. United States. doi:10.1016/j.jcat.2017.02.025.
Luo, Jinyong, Gao, Feng, Kamasamudram, Krishna, Currier, Neal, Peden, Charles H. F., and Yezerets, Aleksey. Sat . "New insights into Cu/SSZ-13 SCR catalyst acidity. Part I: Nature of acidic sites probed by NH 3 titration". United States. doi:10.1016/j.jcat.2017.02.025.
@article{osti_1347850,
title = {New insights into Cu/SSZ-13 SCR catalyst acidity. Part I: Nature of acidic sites probed by NH 3 titration},
author = {Luo, Jinyong and Gao, Feng and Kamasamudram, Krishna and Currier, Neal and Peden, Charles H. F. and Yezerets, Aleksey},
abstractNote = {In this work we investigated an unusual acidity feature of a Cu/SSZ-13 catalyst used in selective catalytic reduction of NOx with NH3 (NH3-SCR). In particular, this catalyst showed two distinct NH3 desorption peaks in NH3-TPD measurements, in contrast to single, unresolved desorption peaks observed for other Cu-exchanged zeolites conventionally used in the SCR studies, including its isostructural but chemically different analogue Cu/SAPO-34. We further observed that the intensities of the two TPD peaks, which represented the amount of stored NH3, changed in opposite directions in response to progressive mild hydrothermal aging, while the total storage capacity was preserved. We proposed an explanation for this remarkable behavior, by using model reference samples and additional characterization techniques. At least three NH3 storage sites were identified: two distinct populations of Cu sites responsible for low-temperature NH3 storage, and Brønsted acid sites responsible for high-temperature NH3 storage. Contrary to the commonly accepted mechanism that Brønsted acid site loss during hydrothermal aging is driven by dealumination, we concluded that the decline in the number of Brønsted acid sites upon mild hydrothermal aging for Cu/SSZ-13 was not due to dealumination, but rather transformation of Cu sites, i.e., gradual conversion of ZCuOH (Cu2+ singly coordinated with Zeolite) to Z2Cu (Cu2+ doubly coordinated with Zeolite). This transformation was responsible for the increased low-temperature desorption peak in NH3-TPD since each ZCuOH adsorbed ~1 NH3 molecule while each Z2Cu adsorbed ~2 NH3 molecules under the conditions used here. These findings were used in Part II of this series of studies to develop a method for quantifying hydrothermal ageing of industrial Cu/SSZ-13 SCR catalysts. Authors would like to thank Randall Jines for his help with collecting the reactor data, Nancy W. Washton for measuring the NMR data and Tamas Varga for in-situ XRD measurements. FG and CHFP gratefully acknowledge supports from the United States Department of Energy (DOE), Energy Efficiency and Renewable Energy, Vehicle Technologies Office. Part of 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.jcat.2017.02.025},
journal = {Journal of Catalysis},
number = ,
volume = 348,
place = {United States},
year = {Sat Apr 01 00:00:00 EDT 2017},
month = {Sat Apr 01 00:00:00 EDT 2017}
}