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  • Investigation of Sulfur Deactivation on Cu/Zeolite SCR Catalysts in Diesel Application

    Yisun Cheng, Christine Lambert

    Ford Motor Company

    Do Heui Kim, Ja Hun Kwak, Charles H.F. Peden

    Pacific Northwest National Laboratory

    August 4, 2009

    2009 DEER Conference

  • Urea SCR Catalysts in Diesel Application

    Cu, Fe Zeolite catalyst

    Leading candidate for treatment of NOx emission for North America Diesel applications.

    Better options for Heavy-duty Diesel Engines

    Already commercialized in Europe

    Durability issues: Dealumination and zeolite structure collapse due to

    hydrothermal aging at high temperature

    Cu sintering due to the reducing agents

    Poisonings: such as S, P, Zn

    2

  • SOx on Cu/zeolite SCR catalysts

    Sulfur poisoning is still a durability issue for base metal/zeolite SCR catalysts, especially for Cu/Zeolite SCR catalysts.

    Most studies have been based on SO2.

    As DOCs are employed upstream of the SCR catalysts, it is likely that a portion of the SO2 are oxidized into SO3.

    Investigation of the impact of SO3 on Cu/zeolite SCR catalysts is important.

    3

  • Experimental

    Catalysts: Fully formulated monolith Cu/zeolite.

    Six (6) 1x1 samples.

    Procedure: Hydrothermal aging at 670C for 20 hr. S poisoning:

    40ppm for 1.5hr with SO2 or SO3 at

    200C, 300C, 400C

    Total S throughput equivalent to 500 miles with 350ppm sulfur fuel

    DeSOx: 170C to 770C at 5C/min.

    Characterization: XPS, Cu XAFS, Cu XANES

    4

  • SCR Activity Testing Sequence

    Hydrothermal Aging

    Test #1: Baseline

    Sulfation with SO2 or SO3

    Test #2: Sulfation effect 770 oC

    De-Sulfation with O2, H2O and CO2 up to 770C: TPD SOx

    desorption

    Test #3: DeSOx effect 200 oC

    5

  • NOx Activity After Thermal Aging

    100

    90 Almost 100% conversion after 200C

    80

    70 Test1, Sample 1

    60 Test1, Sample 2

    50 Test1, Sample 3

    40 Test1, Sample 4

    30 Test1, Sample 5

    20 Test1, Sample 6 10

    0

    100 125 150 175 200 225 250 275 300 325 350

    Inlet Gas Temperature (C) 6

    NO

    x C

    on

    ve

    rsio

    n (

    %)

  • 300 325 350

    SO2 vs. SO3 The impacts on NOx conversion N

    Ox C

    on

    ve

    rsio

    n (

    %)

    200C SO2, T2

    300C SO2, T2

    400C SO2, T2

    200C SO3, T2

    300C SO3, T2

    400C SO3, T2

    T1

    Significant deactivation by SO3!

    100

    90

    80

    70

    60

    50

    40

    30

    20

    10

    0

    100 125 150

    NOx Conversion SV = 30,000/hr - NO only

    175 200 225 250 275

    Inlet Gas Temperature (C) 7

  • 275 300 325 350

    NOx Activity Recovered after DeSOx

    0

    10

    20

    30

    40

    50

    60

    70

    80

    90

    100

    NO

    x C

    on

    vers

    ion

    (%

    )

    Test1, after thermal aging

    Test2, after SO3 aging at 400C

    Test3, after deSOx

    100 125 150 175 200 225 250

    Inlet Gas Temperature (C) 8

  • SO2 vs. SO3 Sulfur released during deSOx

    SO2 Measurement During DeSOx

    45 MoreSO2 desorptionforthesamplesulfatedwithSO3

    40 SO2/200C/ afterT2

    35 SO2/300C/ afterT2 SO2/400C/ afterT2

    30 SO3/200C/ afterT2

    SO3/300C/ afterT2 25 SO3/400C/ afterT2

    20

    15

    10

    5

    0

    150 250 350 450 550 650 7509

    Inlet Gas T, C

    SO

    2, P

    PM

  • 10

    Sulfated with SO3: XPS S 2p region

    3500

    3000

    2500

    2000

    1500

    1000

    500

    0

    165 170 175 180

    c/s

    Hydrothermal aging

    Sulfated with SO3 at 200C

    Sulfated with SO3 at 300C

    No observable sulfur for the

    sample sulfated with SO2

    Binding Energy (eV)

    Only sulfates exists, only if sulfated with SO3. The sample sulfated with

    SO2 does not contain sulfur on the catalyst.

    Sulfates formed during reaction at 200C is larger than those at 300C.

  • NOx Conversion: sulfated with SO3 at different T

    0

    10

    20

    30

    40

    50

    60

    70

    80

    90

    100

    NO

    x C

    onvers

    ion (

    %)

    Test2, SO3 aged at 200C

    Test2, SO3 aged at 300C

    Test2, SO3 aged at 400C

    Test1, Before Sulfur Aging

    100 125 150 175 200 225 250 275 300 325 350

    Inlet Gas Temperature (C)

    Not much difference in NOx conversion in spite of higher amount of sulfates over the sample aged at 200C than that at 300C.

    11

  • After DeSOx: XPS S 2p region

    Inte

    nsity (

    A. U

    .)

    Sulfated at 300 oC

    Desulfated (300 oC)

    Desulfated (200 oC)

    175 170 165

    Binding Energy (eV)

    Sulfur is completely removed after desulfation for both samples.

    Full recovery of NOx conversion after deSOx can be explained by

    the complete removal of sulfate after deSOx.

    12

  • 13

    ZCuSO4 Most stable adsorbed SOx species

    better than ZCuSO3 or ZCuSO2

    Can we identify the species

    (structure) with XAFS?

  • XAFS (Xray absorption fine structure)

    XAFS = XANES (Xray absorption nearedge spectroscopy) +

    EXAFS (extended Xray absorption fine structure)

    EXAFS can give information about bond lengths, element and coordination number surrounding the atom.

    XANES yields information about the electronic structure of the absorbing atom, including valence and oxidation state.

    XAFS works for a wide variety of samples: amorphous and crystalline; solid, liquid, and gas; magnetic and nonmagnetic, etc..

    14

  • 15

    How about the state of Cu?: Cu XANES study

    Normalized spectra Derivative spectra

    Not much change in Cu after DeSOx

    Not like bulk CuSO4, but highly dispersed CuO

  • Cu XAFS: aged, sulfated with SO3, DeSOx

    16

    Informative, but the 2nd shell structure

    is not obtained due to the noise signal.

    Distance (nm)

    0.0 0.1 0.2 0.3 0.4 0.5 0.6

    FT

    in

    ten

    sit

    y (

    a. u

    .) Distance (nm) 0.30 0.32 0.34 0.36 0.38 0.40 0.42 0.44

    FT

    in

    ten

    sit

    y (a

    . u

    .)

  • Summary of XAFS curve fitting for Cu sample

    Sample Pair CN1 r (nm)2 2(pm2)3 E (eV)

    Cu aged Cu-O 3.50.5 0.1950.001 5711 -3.42.1

    Cu DeSOx Cu-O 3.40.3 0.1950.001 548 -3.41.4

    Cu sulfated Cu-O 3.50.3 0.1950.001 466 -3.51.2

    1Coordination number. 2Coordination distance. 3The Debye-Waller factor accounting thermal and statistical

    vibration. *The many body reduction factor was fixed to 0.9. The fitting ranges were 20 - 139 nm-1 for k and 0.100 0.300 nm for r, respectively. The restraint was applied to the Debye-Waller factor for the multiple scattering.

    Only 1st shell information, which is the same among the samples, is

    available due to the noisy signal.

    17

  • Summary

    SCR activity was significantly reduced for samples poisoned

    by SO3 compared with those by SO2, indicating that sulfur poisoning by SO2 and SO3 are not equivalent, with different poisoning mechanisms and impacts.

    Upon the sulfation with SO3, Sulfur exists as sulfate forms (not bulk CuSO4 form, but highly dispersed CuSO4), but maintain its highly dispersed Cu-O species during SOx and DeSOx, which can explain the reversible recovery of activity after desorption as SO2 at elevated temp.

    This study raises an important sulfur poisoning concern for the systems with DOCs in front of on Cu/zeolite SCR catalysts in diesel engine applications.

    18

  • Acknowledgement Clifford Montreuil and Giovanni Cavataio (Ford) for some testing.

    Prof. Sung June Cho (ChonNam Nat. Unv. of Korea) for analyzing XAFS.

    Funding from the U.S. Department of Energy (DOE), Freedom Car and Vehicle Technologies Program.

    NSLS for the beam time at X19A.

    Studies at PNNL were performed in the Environmental Molecular

    Sciences Laboratory (EMSL), a National Scientific User Facility funded by U.S. DOE, Office of Science/Biological and Environmental Research.

    PNNL is a multi-program national laboratory operated for the U.S. Department of Energy by Battelle Memorial Institute under contract number DE-AC06-76RLO 1830.

    19

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Investigation of Sulfur Deactivation on Cu/Zeolite SCR Catalysts in Diesel Application Yisun Cheng, Christine Lambert Ford Motor Company Do Heui Kim, Ja Hun Kwak, Charles H.F. Peden Pacific Northwest National Laboratory August 4, 2009 2009 DEER Conference
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