Importance of the Cu oxidation state for the SO2-poisoning of a Cu-SAPO-34 catalyst in the NH3-SCR reaction

Peter S. Hammershøi, Peter N. R. Vennestrøm, Hanne Falsig, Anker D. Jensen, Ton V. W. Janssens*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Cu-exchanged zeolites of the CHA structure are state-of-the-art catalysts for selective catalytic reduction of NOx with NH3 in diesel aftertreatment systems. However, these catalysts deactivate in the presence of SO2, which is a constituent of diesel exhaust gas. In this article, the deactivation behavior and mechanisms of a Cu-SAPO-34 catalyst were studied with reactor tests and DFT calculations. Exposure of the catalyst to two different SO2 concentrations and durations, but with the same total SO2 exposure, calculated as the product of partial pressure of SO2 and exposure time, lead to the same degree of deactivation. Exposure of the Cu-SAPO-34 catalyst to SO2 in the presence and absence of NO and NH3 at different temperatures between 200–600 °C showed different trends for the deactivation. Below 400 °C, the S/Cu ratio on the catalyst increased with temperature in absence of NO and NH3, while it decreased with increasing temperature in the presence of NO and NH3. This is explained by the ability of NO and NH3 to reduce Cu(II) to Cu(I). DFT calculations show that SO2 adsorbs more strongly on Cu(I) than on Cu (II). Above 400 °C, the S/Cu ratio decreased with temperature irrespective of the presence of NO and NH3. In all cases, the S/Cu ratio is lower than 1. This is not compatible with extensive deposition of ammonium sulfate when co-feeding SO2, H2O and NH3. A more likely explanation for the deactivation is that SO2 is mainly related to the Cu sites. This is further corroborated by DFT calculations showing that SO2 and SO3, which is possibly formed by oxidation of SO2 over Cu sites, interact similar with Cu in Cu-SAPO-34 and Cu-SSZ-13.
Original languageEnglish
JournalApplied Catalysis B: Environmental
Volume236
Pages (from-to)377-383
ISSN0926-3373
DOIs
Publication statusPublished - 2018

Keywords

  • Cu-CHA
  • Deactivation
  • DFT
  • NH3-SCR
  • SO2 poisoning

Cite this

Hammershøi, Peter S. ; Vennestrøm, Peter N. R. ; Falsig, Hanne ; Jensen, Anker D. ; Janssens, Ton V. W. / Importance of the Cu oxidation state for the SO2-poisoning of a Cu-SAPO-34 catalyst in the NH3-SCR reaction. In: Applied Catalysis B: Environmental. 2018 ; Vol. 236. pp. 377-383.
@article{cb92d7059c0443f6b7b2dc399b37ad59,
title = "Importance of the Cu oxidation state for the SO2-poisoning of a Cu-SAPO-34 catalyst in the NH3-SCR reaction",
abstract = "Cu-exchanged zeolites of the CHA structure are state-of-the-art catalysts for selective catalytic reduction of NOx with NH3 in diesel aftertreatment systems. However, these catalysts deactivate in the presence of SO2, which is a constituent of diesel exhaust gas. In this article, the deactivation behavior and mechanisms of a Cu-SAPO-34 catalyst were studied with reactor tests and DFT calculations. Exposure of the catalyst to two different SO2 concentrations and durations, but with the same total SO2 exposure, calculated as the product of partial pressure of SO2 and exposure time, lead to the same degree of deactivation. Exposure of the Cu-SAPO-34 catalyst to SO2 in the presence and absence of NO and NH3 at different temperatures between 200–600 °C showed different trends for the deactivation. Below 400 °C, the S/Cu ratio on the catalyst increased with temperature in absence of NO and NH3, while it decreased with increasing temperature in the presence of NO and NH3. This is explained by the ability of NO and NH3 to reduce Cu(II) to Cu(I). DFT calculations show that SO2 adsorbs more strongly on Cu(I) than on Cu (II). Above 400 °C, the S/Cu ratio decreased with temperature irrespective of the presence of NO and NH3. In all cases, the S/Cu ratio is lower than 1. This is not compatible with extensive deposition of ammonium sulfate when co-feeding SO2, H2O and NH3. A more likely explanation for the deactivation is that SO2 is mainly related to the Cu sites. This is further corroborated by DFT calculations showing that SO2 and SO3, which is possibly formed by oxidation of SO2 over Cu sites, interact similar with Cu in Cu-SAPO-34 and Cu-SSZ-13.",
keywords = "Cu-CHA, Deactivation, DFT, NH3-SCR, SO2 poisoning",
author = "Hammersh{\o}i, {Peter S.} and Vennestr{\o}m, {Peter N. R.} and Hanne Falsig and Jensen, {Anker D.} and Janssens, {Ton V. W.}",
year = "2018",
doi = "10.1016/j.apcatb.2018.05.038",
language = "English",
volume = "236",
pages = "377--383",
journal = "Applied Catalysis B: Environmental",
issn = "0926-3373",
publisher = "Elsevier",

}

Importance of the Cu oxidation state for the SO2-poisoning of a Cu-SAPO-34 catalyst in the NH3-SCR reaction. / Hammershøi, Peter S.; Vennestrøm, Peter N. R.; Falsig, Hanne; Jensen, Anker D.; Janssens, Ton V. W.

In: Applied Catalysis B: Environmental, Vol. 236, 2018, p. 377-383.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Importance of the Cu oxidation state for the SO2-poisoning of a Cu-SAPO-34 catalyst in the NH3-SCR reaction

AU - Hammershøi, Peter S.

AU - Vennestrøm, Peter N. R.

AU - Falsig, Hanne

AU - Jensen, Anker D.

AU - Janssens, Ton V. W.

PY - 2018

Y1 - 2018

N2 - Cu-exchanged zeolites of the CHA structure are state-of-the-art catalysts for selective catalytic reduction of NOx with NH3 in diesel aftertreatment systems. However, these catalysts deactivate in the presence of SO2, which is a constituent of diesel exhaust gas. In this article, the deactivation behavior and mechanisms of a Cu-SAPO-34 catalyst were studied with reactor tests and DFT calculations. Exposure of the catalyst to two different SO2 concentrations and durations, but with the same total SO2 exposure, calculated as the product of partial pressure of SO2 and exposure time, lead to the same degree of deactivation. Exposure of the Cu-SAPO-34 catalyst to SO2 in the presence and absence of NO and NH3 at different temperatures between 200–600 °C showed different trends for the deactivation. Below 400 °C, the S/Cu ratio on the catalyst increased with temperature in absence of NO and NH3, while it decreased with increasing temperature in the presence of NO and NH3. This is explained by the ability of NO and NH3 to reduce Cu(II) to Cu(I). DFT calculations show that SO2 adsorbs more strongly on Cu(I) than on Cu (II). Above 400 °C, the S/Cu ratio decreased with temperature irrespective of the presence of NO and NH3. In all cases, the S/Cu ratio is lower than 1. This is not compatible with extensive deposition of ammonium sulfate when co-feeding SO2, H2O and NH3. A more likely explanation for the deactivation is that SO2 is mainly related to the Cu sites. This is further corroborated by DFT calculations showing that SO2 and SO3, which is possibly formed by oxidation of SO2 over Cu sites, interact similar with Cu in Cu-SAPO-34 and Cu-SSZ-13.

AB - Cu-exchanged zeolites of the CHA structure are state-of-the-art catalysts for selective catalytic reduction of NOx with NH3 in diesel aftertreatment systems. However, these catalysts deactivate in the presence of SO2, which is a constituent of diesel exhaust gas. In this article, the deactivation behavior and mechanisms of a Cu-SAPO-34 catalyst were studied with reactor tests and DFT calculations. Exposure of the catalyst to two different SO2 concentrations and durations, but with the same total SO2 exposure, calculated as the product of partial pressure of SO2 and exposure time, lead to the same degree of deactivation. Exposure of the Cu-SAPO-34 catalyst to SO2 in the presence and absence of NO and NH3 at different temperatures between 200–600 °C showed different trends for the deactivation. Below 400 °C, the S/Cu ratio on the catalyst increased with temperature in absence of NO and NH3, while it decreased with increasing temperature in the presence of NO and NH3. This is explained by the ability of NO and NH3 to reduce Cu(II) to Cu(I). DFT calculations show that SO2 adsorbs more strongly on Cu(I) than on Cu (II). Above 400 °C, the S/Cu ratio decreased with temperature irrespective of the presence of NO and NH3. In all cases, the S/Cu ratio is lower than 1. This is not compatible with extensive deposition of ammonium sulfate when co-feeding SO2, H2O and NH3. A more likely explanation for the deactivation is that SO2 is mainly related to the Cu sites. This is further corroborated by DFT calculations showing that SO2 and SO3, which is possibly formed by oxidation of SO2 over Cu sites, interact similar with Cu in Cu-SAPO-34 and Cu-SSZ-13.

KW - Cu-CHA

KW - Deactivation

KW - DFT

KW - NH3-SCR

KW - SO2 poisoning

U2 - 10.1016/j.apcatb.2018.05.038

DO - 10.1016/j.apcatb.2018.05.038

M3 - Journal article

VL - 236

SP - 377

EP - 383

JO - Applied Catalysis B: Environmental

JF - Applied Catalysis B: Environmental

SN - 0926-3373

ER -