an “in situ” infrared and xas study on no - cleers...an “in-situ” infrared and xas study on...
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An “in-situ” infrared and XAS study on NO
adsorption on Pd/zeolite under complex gas feed
Donna Liu, Loredana Mantorosie, H. Islam, V. Novak, M. Sarwar,
H.Y. Chen, J. E. Collier and D. Thompsett
Outline
• Challenges in controlling NOx emission during cold start period
• Palladium zeolite as passive NOx adsorber
• Effect of H2O on NOx adsorption/release
• Effect of CO on NOx adsorption/release
• Effect of SO2 on NOx adsorption/release
• Conclusions
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Challenges in controlling NOx emission during cold start period
• Reduction of NOx emissions from lean burn
diesel engines is essential to meet current
and future legislation standards;
• e.g. SULEV30, Engine-out HC/NOx emissions
exceed the limit during the cold start period;
• Current NOx control technologies, NSR or
Urea-SCR function at temperature > ~
200°C;
• Therefore, NOx emission control during the
cold start period is becoming a significant
challenge
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HC + NOx SULEV30
Zeolite supported Pd catalysts exhibit high NO storage capacity & trapping efficiency; Zeolite FW shows a strong impact on storage window
4
1.H.-Y. Chen et al.; Catal. Lett.; June2016; DOI 10.1007/s10562-016-1794-62.R.Rajaram et al.; US Patent 2015/0158019
Adsorption at 100°C200ppm NO, 200ppm CO, 500ppm C10H22(C1), 5%H2O, 10%O2, 5% CO2
SV 30K/hr
NO storage is due to NO direct adsorption on isolated Pd2+ sites
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NO
Pd2+
NO+
NO2+
NO3+
1.H.-Y. Chen et al.; Catal. Lett.; June2016; DOI 10.1007/s10562-016-1794-6
Individual gas, such as H2O or CO, show influence on NO adsorption on Pd.Z
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--- NO+O2--- NO+O2+H2O--- NO+CO+O2--- NO+CO+O2+H2O
(full lines NO; dashed lines NO2)
Test conditions:1%Pd/CHAAdsorption at 100°C, 100ppm NO, 200ppm CO, 5%H2O, 10%O2.
H2O
CO
• With or without CO, waterinhibits NO adsorption at100°C.
• With absence of water, COhas no effect on NOadsorption.
• When water is present, COimproves NO storage.
Individual gas, such as H2O or CO, show influence on NO adsorption on Pd.Z
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--- NO+O2--- NO+O2+H2O--- NO+CO+O2--- NO+CO+O2+H2O
(full lines NO; dashed lines NO2)
Test conditions:1%Pd/CHAAdsorption at 100°C, 100ppm NO, 200ppm CO, 5%H2O, 10%O2.
H2O
CO
• With or without CO, waterinhibits NO adsorption at100°C.
• With absence of water, COhas no effect on NOadsorption.
• When water is present, COimproves NO storage.
Water inhibits NO adsorption at low temperatures (< = 100C)but enhances NO adsorption as temperature increases above 100C
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--- 80°C--- 100°C--- 120°C--- 150°C
--- 80°C--- 100°C--- 120°C--- 150°C
NO+O2 NO+H2O+O2
• In the absence of water, less NO stored at higher temperatures.
• H2O inhibits NO storage at low temperatures.• As temperature is increased, more NO is stored
Water severely inhibits NO adsorption on Brönsted acid sites and surface nitrates, less affects NO adsorption on isolated Pd2+ sites
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---NO+O2
---NO+O2+H2O
• NO, NO+, NO3-, NO2- are present on Pd/CHA;• H2O is significantly suppressing NO+ adsorption on
Brönsted acid sites as well as nitrates/nitrites;
Pd2+
Pd0
• In-situ XAS study suggests electronic enrichment on Pdand increase in the number of coordinated species.
Water increases the strength of NO adsorption by electronic enrichment on Pd2+ ion at temperature above 100C
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• At low T, water inhibits some NOadsorption sites;
• When temperature goes up, waterincreases the strength of NO adsorption byelectronic enrichment on Pd2+ ions;
Presence of H2O enhances NO binding energy
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Presence of water delays NO desorption due to stronger binding energy
--- NO+O2--- NO+O2+H2O--- NO+CO+O2--- NO+CO+O2+H2O
• With absence of water, NOx desorbsas soon as the temperatureincreases;
• Presence of water delays NOdesorption.
H2O
Test conditions:1%Pd/CHAAdsorption at 100°C, 100ppm NO, 200ppm CO, 5%H2O, 10%O2, then ramp up
Individual gas, such as H2O or CO, show influence on NO adsorption on Pd.Z
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--- NO+O2--- NO+O2+H2O--- NO+CO+O2--- NO+CO+O2+H2O
(full lines NO; dashed lines NO2)
Test conditions:1%Pd/CHAAdsorption at 100°C, 100ppm NO, 200ppm CO, 5%H2O, 10%O2.
H2O
CO
• With or without CO, waterinhibits NO adsorption at100°C.
• With absence of water, COhas no effect on NOadsorption.
• When water is present, COimproves NO storage.
0
20
40
60
80
100
120
0 100 200 300 400 500 600
NO
x (
pp
m)
Time (s)
100ppm NO + 200ppm CO
100ppm NO + 500ppm CO
100ppm NO + 750ppm CO
100ppm NO + 1500ppm CO
Increase CO concentration improves NO adsorption
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Test conditions:1%Pd/CHAAdsorption at 100°C, 100ppm NO, x ppm CO, 130 ppm C3H6, 5%H2O, 10%O2,
Higher CO concentrations cause earlier NO release
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0
40
80
120
160
200
100 150 200 250 300 350 400 450
NO
x &
CO
(p
pm
)
Temp (C)
100ppm NO + 200ppm CO100ppm NO + 500ppm CO100ppm NO + 750ppm CO100ppm NO + 1500ppm CO
Test conditions:1%Pd/CHAAdsorption at 100°C, 100ppm NO, x ppm CO, 130 ppm C3H6, 5%H2O, 10%O2,
CO, in combination with water, provides electronic enrichment to Pd sites, enhancing NO adsorption
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--- NO+O2--- NO+O2+H2O
--- NO+CO+O2--- NO+CO+O2+H2O
• Same type of NO adsorbed species are observed in thepresence of CO.
• Presence of water and CO enhances NO adsorption.
Pd0
Pd2+
• In-situ XAS shows significant electronic enrichment whenboth CO and NO are present.
• More coordination around Pd sites is observed.
CO reduces higher Pd oxidation states to +2, which is favourablefor NO adsorption
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200020502100215022002250
Wavenumber (cm-1)
Pdn+ (n=1-4)
Applied Catalysis B: Environmental
Volume 147, 5, 2014, 764–769
• Water and CO co-existence is essential
FTIR spectra of CO adsorption on Pd/CHA
NO storage is due to NO direct adsorption on isolated Pd2+ sites
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NO
Pd2+
NO+
NO2+
NO3+
1.H.-Y. Chen et al.; Catal. Lett.; June2016; DOI 10.1007/s10562-016-1794-6
Sulfur does not affect the NO storage function due to different mechanism
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0
0.2
0.4
0.6
0.8
Initial 0.5 g S/Lcat.
1 g S/Lcat.
2 g S/Lcat.
NO
x s
tora
ge c
apacity
(gN
O2/L
cat.
)
• Sulfur doesn’t impacts NOadsorption
Sulfur affects CO oxidation activities and delays NOx release to higher temperature
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0
200
400
600
800
1000
100 150 200 250 300 350
NO
x (
ppm
)
Inlet Temp (C)
Initial0.5 g S/L1 g S/L2 g S/L
0
50
100
150
200
250
300
350
400
0
50
100
150
200
250
0 200 400 600 800 1000
Inle
t T
CO
(ppm
)
Time (s)
Initial
0.5 g S/L
1 g S/L
2 g S/L
Test conditions:1%Pd/CHAAdsorption at 125°C, 200ppm NO, 200ppm CO, 5%H2O, 10%O2, then ramp up
Conclusions
• Pd.Z exhibits high NO storage at low temperature, which is a key component in dCSC™
catalysts
• NO directly adsorbs on isolated Pd2+ sites
• Water inhibits some NO adsorption at low T, but enhances NO adsorption as temperature
increases
• CO, in combination with H2O, enhances NO adsorption
• High CO concentration is detrimental as it lowers NOx release temperature
• Sulfur doesn’t affects NO adsorption function and delays NO release to higher temperature
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