1. Lifetime impact of SO2-poisoning of Cu-CHA catalysts for NH3-SCR
Peter S. Hammershøi, Anker D. Jensen and Ton V. W. Janssens
CLEERS 2018, Ann Arbor, MI

2. Please Note: This contents of presentation has been published in:
[1] P.S. Hammershøi, P.N.R. Vennestrøm, H. Falsig, A.D. Jensen, T.V.W. Janssens, Importance of the Cu oxidation state for the SO 2 -poisoning of a Cu-SAPO-34 catalyst in the NH 3 -SCR reaction, Appl. Catal. B Environ. 236 (2018) 377–383. doi: /j.apcatb
[2] P.S. Hammershøi, A.D. Jensen, T.V.W. Janssens, Impact of SO 2 -poisoning over the lifetime of a Cu-CHA catalyst for NH 3 -SCR, Appl. Catal. B Environ. 238 (2018) 104–110. doi: /j.apcatb
Please refer to these publications to cite from this presentation.
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Umicore Template 2017

3. Diesel exhaust and NH3-SCR
Diesel exhaust gas contains NOx (NO and NO2) and SO2 (1-2 ppmv)
Selective catalytic reduction (SCR) with NH3:
4 NO + 4 NH3 + O2 → 4 N2 + 6 H2O
SCR catalysts: V2O5-based, Fe-zeolites and Cu-zeolites
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4. Background and aims Background: Colder exhaust gas in near future:
Better fuel efficiency → lower CO2 emissions
Better cold start performance
Hybrids
Superior low-temperature activity of Cu-zeolites
Main disadvantage of Cu-zeolites is SO2-poisoning
Questions:
What causes the deactivation by SO2?
Is the lifetime impact of SO2 prohibitive for practical application?
SO2
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5. What causes the deactivation by SO2?
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6. Cu-CHA catalyst and deactivation mechanisms
Cu-CHA catalysts
Microporous structure
SCR activity from Cu sites
Blocking of Cu sites by SO2 or,
pore-blocking by deposition of ammonium sulfates?
CHA framework
Adapted from
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7. Deactivation by blocking of Cu sites
SO2 in SCR gas: SO2/Cu lower than 1
No deposition of ammonium sulfate
SO2+O2+H2O: SO2/Cu higher than 0
Cu,S interactions!
Different trends for SO2/Cu vs temperature – related to Cu,S chemistry?
SCR gas: ppmv NO 530 ppmv NH3 10 % O2 5 % H2O
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Adapted from Hammershøi et al. Appl. Catal. B (2018), 236,
CLEERS 2018

8. Cu,S interactions by DFT
SO2 prefers Z-CuI
SO3 prefers Z-CuIIOH
Z-CuI +
Z-CuIIOH +
SO2
Z-CuI··SO2 (ΔE = eV)
Z-CuIIHSO3 (ΔE = eV)
SO3
Z-CuI··SO3 (ΔE = eV)
Z-CuIIHSO4 (ΔE = eV)
Adapted from Hammershøi et al. Appl. Catal. B (2018), 236,
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9. Effect of NH3 on Cu oxidation state
SCR-gas conditions
Only way to have CuI is to have NH3 present:
High [NH3] → CuI
Low [NH3] → CuII
CuII
CuI
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Janssens et al., ACS Catal. 5, (2015)
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10. Effect of temperature [CuI] [NH3] ↓ [CuII] [SO2] SO2 oxidation rate ↑
Increasing temperature:
[CuI]
[NH3] ↓
[CuII]
[SO2]
SO2 oxidation rate ↑
[SO3]
Low T
High T
With SCR gas
CuI + SO2
CuII + SO3
Without SCR gas
CuII + SO2
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11. Importance of Cu oxidation state
SO2 in SCR gas: CuI and CuII present
Adsorption effect
SO2+O2+H2O: only CuII
Increased oxidation rate of SO2 to SO3
Similar trends above 400 °C – effectively similar exposure conditions
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Adapted from Hammershøi et al. Appl. Catal. B (2018), 236,
CLEERS 2018

12. What is the lifetime impact of SO2?
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13. SO2-poisoning behavior of Cu-CHA
Low-temperature NOx conversion drops after SO2 exposure
Heating to 550 °C partially restores NOx conversion
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14. Impact of SO2 concentration and exposure time
Deactivation appears to depend on: SO2 concentration · exposure time [ppm·h]
Deactivation can be accelerated
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15. SO2/Cu exposure over a catalyst lifetime
Assumptions for lifetime SO2 exposure of a Cu-CHA SCR catalyst in a heavy-duty vehicle
Distance: km
Fuel efficiency: L/ 100 km
Sulfur content in diesel: 5 wt ppm (converts to ppmv SO2 in exhaust) (Ultra-low sulfur diesel: EU <10 wt ppm, USA <15 wt ppm)
Catalyst: 1.5 kg Cu-CHA with 3 wt% Cu: 45 g Cu
Potential total lifetime exposure: SO2/Cu = 44
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16. Lifetime deactivation experiments
SO2+O2+H2O exposure
Regeneration
1-120 °C Total SO2/Cu = 42
Cu-CHA: Si/Al Cu/Al 0.42
6 °C in SO2- free gas
ICP: S/Cu
ICP: S/Cu
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17. ICP: sulfur uptake – S/Cu ratio
Sulfur uptake faster at °C
With NO+NH3 S/Cu at 200 °C should increase
Regenerated S/Cu similar for all temperatures
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18. Lifetime deactivation of a Cu-CHA catalyst
(solid lines: deactivation at 200 °C – dashed lines: S/Cu by ICP)
S/Cu ratios increase in parallel to deactivation
Deactivation occurs fast!
After 1 % of the total lifetime SO2/Cu exposure, deactivation is above 70 %
Deactivation level ≠ S/Cu ratio
Regeneration can limit deactivation to 20 %
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19. Conclusions Deactivation by Cu,S species – not ammonium sulfates
Interactions of SO2 and SO3 depend on Cu oxidation state
Deactivation occurs fast
Regeneration is possible at 550 °C in SO2-free gas
The use of Cu-CHA catalysts is contingent on:
efficient regeneration and,
use of ultra-low sulfur diesel
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20. Thanks to collaborators!
PhD student: Peter S. Hammershøi Technical University of Denmark (DTU): Professor Anker D. Jensen Umicore Denmark ApS: Principal Scientist Peter N.R. Vennestrøm Research Specialist Jesper S. Larsen Haldor Topsøe A/S: Research Scientist Hanne Falsig Innovation Fund Denmark
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21. Thank you for your attention