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

2

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

3

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

5

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

6

--- 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

7

--- 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

10

• 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

12

--- 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

14

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

16

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

18

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

19

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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