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Understanding the Deactivation Mechanisms of Cu/Zeolite SCR

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  • Understanding the Deactivation Mechanisms of Cu/Zeolite

    SCR Catalysts in

    Diesel Application

    Yisun Cheng, Christine LambertResearch & Innovation Center, Ford Motor Company

    Ja

    Hun Kwak, Charles H.F. PedenInstitute for Interfacial Catalysis, PNNL

    August 5, 20082008 DEER Conference

  • 2

    Introduction

    The effects of engine and lab aging on Cu/zeolite SCR catalysts reactivity and material properties

    were assessed by performance tests and multiple characterization techniques that included 27Al NMR, XRD, and TEM.

    The impacts of zeolite

    structure, Cu sites, and active sites

    on SCR catalyst durability are discussed.

    The results aid the development of the understanding of Cu/zeolite

    SCR catalyst

    deactivation mechanisms in diesel application.

  • 3

    The Durability of Cu/Zeolite

    SCR Catalysts

    Zeolite Structure:Increasing the collapsing temp to maintain zeolite structure during thermal aging is the key for Cu/zeolite

    SCR Catalysts in Diesel Application.

    Active Sites

    Durability

    Cu Sites

  • 4

    Zeolite

    Stability

    Thermal Deactivation

    Fresh (Cat A) Lab 860/30min (Cat A) Lab 770C/30min (Cat A)

    770C/30min: Zeolite crystal structure maintained

    860/30min: Zeolite structure collapsed. Large particles of amorphous alumino-silicate are formed (XRD)

    No evidence for Cu sintering 0102030405060708090

    100

    100 150 200 250 300 350 400 450 500 550 600Catalyst Temperature, C

    Con

    vers

    ion,

    %NOx conv 100% NO FreshNOx conv 100% NO 770C 30minNOx conv 100% NO 860C 30min

  • 5

    Cordierite (honey comb)

    Cat A

    fresh

    Cat A

    770 C 30 min aged

    Cat A

    860 C 30 min aged

    XRD (Cat A)

    Zeolite structure mostly stable after 770 C treatments

    Only amorphous phase remained after 860 C 30 min aged Zeolite structure collapsed for 860 C treatment

    SCR Deactivation Mechanism

    Zeolite

    Durability

    5 10 15 20 25 30 35 40 45

    2 theta

  • 6

    SCR Deactivation Mechanism Understanding

    Zeolite Structure

    Cu Sites:

    Found Cu sintering on engine aged samples, especially the gas inlet section.

    Cu sintering seems to be controlled by gas phase chemistry rather than the aging temp.

    Active Sites

    Durability

  • 7

    SCR Deactivation Mechanism

    Cu Sites

    Fresh Cat B

    Engine 120K 1st

    inch Cat B

    Basically same morphology as the fresh material

    Very (!!) significant Cu sintering behavior evident (consistent with XRD and EPMA)

  • 8

    SCR Deactivation Mechanism Cu Sites

    120K 1st

    inchCat C

    120K 7th inchCat C

    Basically same morphology.No evidence of Cu sintering

    on the 7th.Some minor portion shows Cu

    sintering behavior on the 1st.

    Cu sintering behavior

    NOx Conversion, SV=30K, 350ppmNO/350ppm NH3

    0

    10

    20

    30

    40

    50

    60

    70

    80

    90

    100

    100 150 200 250 300 350 400 450 500 550 600Catalyst T, C

    NO

    x C

    onve

    rsio

    n

    NOx conv 100% NO B1-1(test1)

    NOx conv 100% NO B1-7

  • 9

    Cu still located inside

    not sintered on the external surface of the oxide particle

    SCR Deactivation Mechanism

    Cu SitesLab 860/30min (Cat A)

    Serious Cu sintering after the NH3

    TPD.

    Aging at 700C under O2 atmosphere

    no serious sintering.

    Reduction with H2

    flow

    sintering started

  • 10

    SCR Deactivation Mechanism Understanding

    Zeolite StructureActive Sites:

    The overall activity is not high if the Al is not stable in the framework structure of zeolite

    (dealumination).

    Acidity of SCR catalysts reflects the status of active sites.

    Not only the thermal factor, but also chemical

    factors, such as reductants

    and urea, impact the stability of active sites.

    Durability

    Cu Sites

  • 11

    SCR Deactivation Mechanism

    Active Sites

    It is known that surface acidity is important for ammonia SCR reaction.

    Characterize the acidity through measuring adsorbed NH3 that associated to the acid sites on the catalysts. But, can not measure the types (Bronsted

    or Lewis) of acid sites.

    The overall acidity of SCR reflects its activity.

    NOx Conversion, Engine 120K, Cat B

    0102030405060708090

    100

    100 150 200 250 300 350 400 450 500 550 600Catalyst Temperature, C

    Con

    vers

    ion,

    %

    NOx conv 100% NO 120K Eng. Aged 1-3NOx conv 100% NO 120K Eng. Aged 1-5NOx conv 100% NO 120K Eng. Aged 1-8

    NH3 TPD, Engine 120K, Cat B

    0

    20

    40

    60

    80

    100

    120

    140

    150 200 250 300 350 400 450Catalyst Temperature, C

    NH

    3, P

    PM

    120K Engine Aged, 1st120K Engine Aged, 3rd120K Engine Aged, 5th120K Engine Aged, 8th

  • 12

    0

    500

    1000

    1500

    2000

    2500

    3000

    3500

    4000

    4500

    5000

    Rela

    tive

    loss

    of t

    etra

    hedr

    al A

    l(a.u

    .)1st 2nd+3rd 4th 5th 6th+7th 8th

    304050607080

    Chemical Shift(ppm)

    1st2nd+3rd4th5th6th+7th8th

    Subtraction from fresh: relative loss of Altet

    SCR Deactivation Mechanism

    Active Sites

    The decreasing of acidity is not the only factor that causes the decreasing of SCR activity.

    Relative loss of Altet

    (Engine 120K, Cat B) from NMR data

  • 13

    -100-50050100150

    Chemical shift(ppm)

    Fresh

    770oC 30min aged

    770oC 30min wet urea

    860oC 30min aged

    47ppm

    *

    *

    *: spinning side band

    SCR Deactivation Mechanism

    Active Sites

    860 C 30 min aged sample: no evidence for tetrahedral aluminum which means decompose of zeolite structure.

    770 C 30 min aged: no significant change from fresh sample.

    770 C 30 min wet urea: less amount of tetrahedral aluminum which indicate some dealumination.

    0102030405060708090

    100

    100 150 200 250 300 350 400 450 500 550 600Catalyst Temperature, C

    Con

    vers

    ion,

    %

    NOx conv 100% NO FreshNOx conv 100% NO 860C 30minNOx conv 100% NO 770C 30minNOx conv 100% NO 770C 30min urea/wet

    Solid state 27Al-NMR

  • 14

    Active Sites

    Acidity and Relative Dealumination

    304050607080

    Chemical shift(ppm)

    770C 30min770C wet urea860C 30 min

    Relative DealuminationNH3 TPD, Cat A

    0

    50

    100

    150

    200

    250

    150 200 250 300 350 400 450Catalyst Temperature, C

    NH

    3, P

    PM

    Degreened860C 30min770C 30min770C 30min urea/wet

    Aging factors impact SCR acidity differently.

  • 15

    SUMMARY

    The stability of zeolite

    structure, Cu sites, and active

    sites

    all contribute to the durability of SCR catalysts. They are correlated with each other and equally important.

    Dealumination, zeolite

    structure damage, base metal sintering are the root causes of SCR deactivation.

    Some aging conditions impact all three features, but some might just impact one or two or them.

    There are lots of unknowns that need to be investigated

    Zeolite

    structure, Cu sites, and active sites each contribute

    to the SCR catalyst durability.

    Control of the aging factors to minimize the impact on Cu/zeolite

    SCR catalysts in diesel applications.

  • 16

    ACKNOWLEDGEMENTS

    Financial support for studies performed at Pacific Northwest National Laboratory (PNNL) was provided by the U.S. Department of Energy (DOE), Office of FreedomCar

    and Vehicle Technologies.

    Portions of the work were performed in the Environmental Molecular Sciences Laboratory (EMSL) at the PNNL. The EMSL is a national scientific user facility and supported by the U.S. DOE Office of Biological and Environmental Research.

    Understanding the Deactivation Mechanisms of Cu/Zeolite SCR Catalysts in Diesel ApplicationIntroductionThe Durability of Cu/Zeolite SCR CatalystsZeolite Stability Thermal DeactivationSlide Number 5SCR Deactivation Mechanism UnderstandingSCR Deactivation Mechanism Cu SitesSCR Deactivation Mechanism Cu SitesSlide Number 9SCR Deactivation Mechanism UnderstandingSlide Number 11Slide Number 12SCR Deactivation Mechanism Active SitesActive Sites Acidity and Relative DealuminationSUMMARYACKNOWLEDGEMENTS

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