+ All Categories
Home > Documents > Modeling the impact of aging on active sites in Cu-Zeolite ......reduction with ammonia over...

Modeling the impact of aging on active sites in Cu-Zeolite ......reduction with ammonia over...

Date post: 10-Feb-2021
Category:
Upload: others
View: 0 times
Download: 0 times
Share this document with a friend
26
On kinetic modeling of change in active sites upon hydrothermal aging of Cu-SSZ-13 Rohil Daya , Saurabh Joshi, Jinyong Luo, Rama Krishna Dadi, Neal Currier, Aleksey Yezerets Public 09-18-2019 CLEERS 2019 Workshop
Transcript
  • On kinetic modeling of change in active sites upon hydrothermal aging of Cu-SSZ-13

    Rohil Daya, Saurabh Joshi, Jinyong Luo, Rama Krishna Dadi, Neal Currier, Aleksey Yezerets

    Public

    09-18-2019

    CLEERS 2019 Workshop

  • 2Public

    Outlineβ–ͺ Motivation and Background

    β–ͺ Modification of reaction rate forms to account for active site dynamics

    β–ͺ Developing constitutive relations for Hydrothermal Aging of Cu-SSZ-13

    β–ͺ Summary and Future Work

  • 3Public

    Motivation – Tailpipe NOx and Durability Requirements

    Future Application Challenges

    2024+

    Challenge

    Real World 90%NOx

    Add heat/CDA/ bypass

    Sustained LT

    Cold start

    GHG Reduction

    Engine efficiency

    Electrification

    Fuel type

    …

    Emission Warranty Extension

    Forecast 2022 2024

    HD 5Y 350K miles 5Y 435K miles ( maybe longer)

    MD 5Y 150K miles 5Y 185K miles ( maybe longer)

    Overall approach to meet these challenges

    includes

    a) Adaptable Controls

    b) Improved understanding and modeling

    of real world aging

    c) Improved Component durability (higher

    resistance to real world aging)Class 2022 2027 (forecast)

    HD 5Y 350K miles 14Y 800K miles

    MD 5Y 150K miles 14Y 400K miles

  • 4

    Two chemically distinct monomeric Cu2+ active sites in Cu-SSZ-13; typically solvated and mobile

    under reaction conditions; undergo redox during SCR (Cu1+ observed during standard SCR)

    Mild-hydrothermal aging leads to

    decrease in number density of ZCuOH sites (𝛺𝑍𝐢𝑒𝑂𝐻),and concomitant increase in number density of Z2Cu

    sites (𝛺𝑍2𝐢𝑒) [1]. Severe HTA leads to dealumination,

    increase in CuOx, and eventually structural collapse

    Public

    Active Sites in Cu-SSZ-13 and influence of aging

    Hydrothermal Aging Sulfur Poisoning

    ZCuOH

    Z2Cu

    [1] Luo, J., An, H., Kamasamudram, K., Currier, N., Yezerets, A., Watkins, T., & Allard, L.

    (2015). Impact of Accelerated Hydrothermal Aging on Structure and Performance of Cu-SSZ-

    13 SCR Catalysts. SAE International Journal of Engines, 8(3), 1181-1186.

    Sulfur selectively poisons Copper sites.

    ZCuOH stores more sulfur and is harder to

    regenerate relative to Z2Cu [2]

    [2] Shih, A. J., Khurana, I., Li, H., GonzΓ‘lez, J., Kumar, A., Paolucci, C., ... & Yezerets, A.

    (2019). Spectroscopic and kinetic responses of Cu-SSZ-13 to SO2 exposure and implications

    for NOx selective catalytic reduction. Applied Catalysis A: General, 574, 122-131.

  • 5

    Monolith reactors can be modeled as plug flow reactors. Equations below

    are sufficient to describe SCR behavior under realistic operating conditions

    Public

    Classical Conservation Equations for Monolith

    Reactors

    π’–ππ’šπ’Šππ’›

    = βˆ’πŸ’π’Œπ’Ž,π’Šπ’…π’‰π’šπ’…

    (π’šπ’Š βˆ’ π’šπ’Šπ’˜π’„)𝝂𝒋,π’Šπ’“π’‹

    π‘ͺ𝟎= βˆ’π‘«π’†π’‡π’‡

    ππŸπ’šπ’Šπ’˜π’„ππ’™πŸ

    πœ΄π’Žππœ½π’Œππ’•

    = 𝝂𝒋,π’Šπ’“π’‹

    Convection Rate = Diffusion Rate Surface Coverage ConservationReaction Rate = Diffusion Rate

    π’Œπ’Ž,π’Š π’šπ’Š βˆ’ π’šπ’Šπ’˜π’„ = βˆ’π‘«π’†π’‡π’‡ππ’šπ’Šπ’˜π’„ππ’™

    𝒂𝒕 𝒙 = 𝟎subject to

    [3] Copeland, C., Pesiridis, A., Martinez-Botas, R., Rajoo, S., Romagnoli, A., & Mamat, A.

    (2014). Automotive Exhaust Waste Heat Recovery Technologies. In Automotive Exhaust

    Emissions and Energy Recovery. Nova Science Publishers.

    Copeland et al. [3]

    0 200 400 600 800 1000 1200

    Cu

    mu

    lati

    ve N

    Ox

    [g]

    Time [s]

    Hot FTP Cumulative NOx

    SCR-In NOxSCR-Out ExpSCR-Out Model

    0 200 400 600 800 1000 1200

    NH

    3[p

    pm

    ]

    Time [s]

    Hot FTP NH3 Slip

    SCR-Out Exp

    SCR-Out Model

  • 6

    β–ͺ Aging induces changes in catalyst state. These changes can be modeled in a classical framework

    by deriving:

    a) Constitutive relations/rate expressions for quantitative changes of all chemically distinct active sites

    b) Intrinsic, site specific turnover rates for conversion of gas species on each active site

    β–ͺ In this representation, the state and behavior of each active site is defined completely by a set of

    variables and constants with respect to aging

    β–ͺ This entails a combination of reaction engineering and more fundamental approaches incorporating

    DFT predictions and microkinetics

    β–ͺ In the next few slides, we will show a first effort at developing constitutive relations for the change in

    active sites induced by hydrothermal aging of Cu-SSZ-13 Public

    Incorporating Aging in Conservation Equations

    πœ΄π’Žππœ½π’Œππ’•

    = 𝝂𝒋,π’Šπ’“π’‹ πœ΄π’Žβ€² (π’•π’‚π’ˆπ’†, π‘»π’‚π’ˆπ’†, 𝑺𝑢𝒙… )

    ππœ½π’Œππ’•

    = 𝝂𝒋,π’Šπ’“π’‹β€²(π’•π’‚π’ˆπ’†, π‘»π’‚π’ˆπ’†, 𝑺𝑢𝒙… )

    Fixed Age Variable Age

    Z2Cu

    Variable : 𝛺𝑍2𝐢𝑒 (π‘›π‘’π‘šπ‘π‘’π‘Ÿ 𝑑𝑒𝑛𝑠𝑖𝑑𝑦)

    Constants (if fixed turnover rate) : 𝐴𝑁𝐻3𝐴𝑑𝑠 𝑍2𝐢𝑒 ,

    βˆ†π‘†π‘π»3𝐴𝑑𝑠 𝑍2𝐢𝑒 , βˆ†π»π‘π»3𝐴𝑑𝑠 𝑍2𝐢𝑒 , 𝐴𝑆𝐢𝑅𝑍2𝐢𝑒 , πΈπ‘Žπ‘†πΆπ‘… 𝑍2𝐢𝑒…

    ZCuOH

    Variable : 𝛺𝑍2𝐢𝑒 (π‘›π‘’π‘šπ‘π‘’π‘Ÿ 𝑑𝑒𝑛𝑠𝑖𝑑𝑦)

    Constants (if fixed turnover rate) : 𝐴𝑁𝐻3𝐴𝑑𝑠 𝑍𝐢𝑒𝑂𝐻 ,

    βˆ†π‘†π‘π»3𝐴𝑑𝑠 𝑍𝐢𝑒𝑂𝐻 , βˆ†π»π‘π»3𝐴𝑑𝑠 𝑍𝐢𝑒𝑂𝐻 , 𝐴𝑆𝐢𝑅𝑍𝐢𝑒𝑂𝐻 , πΈπ‘Žπ‘†πΆπ‘… 𝑍𝐢𝑒𝑂𝐻 …

  • 7Public

    Hydrothermal Aging Model Approach

    NH3 storage kinetics on individual sites

    β€’ Site isolation approach

    β€’ 550Β°C-4h H-SSZ-13 data used for BrΓΈnsted acid site kinetics

    β€’ 750Β°C-4h Cu-SSZ-13 data used for lumped Copper site kinetics.

    β€’ 600Β°C-2h low temperature (

  • 8Public

    Active Sites for NH3 Adsorption on H-SSZ-13β–ͺ It has been shown that on H-SSZ-13, NH4

    + cations are NH3 –solvated below 400Β°C, based on in-

    situ vibrational spectroscopy and DFT simulations [4-5]

    [4] Giordanino, F., Borfecchia, E., Lomachenko, K. A., Lazzarini, A., Agostini, G., Gallo, E., ... & Lamberti, C.

    (2014). Interaction of NH3 with Cu-SSZ-13 catalyst: a complementary FTIR, XANES, and XES study. The

    journal of physical chemistry letters, 5(9), 1552-1559.

    [5] Li, S., Zheng, Y., Gao, F., Szanyi, J., & Schneider, W. F. (2017). Experimental and computational

    interrogation of fast SCR mechanism and active sites on H-Form SSZ-13. ACS Catalysis, 7(8), 5087-5096.

    DFT Optimized Structures [5]

    Strong-H Weak-H

    β–ͺ Furthermore, in-house experimental data for H-SSZ-13 shows indirect evidence of second order adsorption,

    consistent with solvation of NH4+ ions by NH3 . Thus, NH3 adsorption on BrΓΈnsted acid sites modeled as a

    Type-II BET isotherm

    π‘Ÿπ‘βˆ’π‘†π» = π‘˜π‘βˆ’π‘†π»πœƒπ‘.𝑁𝐻4𝛺𝐻

    𝑁𝐻3 + 𝑍𝐻 β‡Ώ 𝑍.𝑁𝐻4π‘Ÿπ‘“βˆ’π‘†π» = π‘˜π‘“βˆ’π‘†π»π‘¦π‘π»3πœƒπ‘π»π›Ίπ»

    𝑁𝐻3 + 𝑍.𝑁𝐻4 β‡Ώ 𝑍.𝑁𝐻4. 𝑁𝐻3π‘Ÿπ‘“βˆ’π‘Šπ» = π‘˜π‘“βˆ’π‘Šπ»π‘¦π‘π»3πœƒπ‘.𝑁𝐻4π›Ίπ»π‘Ÿπ‘βˆ’π‘Šπ» = π‘˜π‘βˆ’π‘†π»πœƒπ‘.𝑁𝐻

    4.𝑁𝐻

    3𝛺𝐻

  • 9Public

    Second Order NH3-Adsorption on H-SSZ-13β–ͺ NH3 release during isothermal adsorption and TPD can be described quantitatively using the Type-II BET

    adsorption model

    β–ͺ Results from typical first order Langmuir/Temkin adsorption model show that while such a model can capture

    the desorption peak with similar accuracy, NH3 release isothermal NH3 adsorption cannot be described

    accurately

    550Β°C-4h H-SSZ-13 NH3 TPD 550Β°C-4h H-SSZ-13 Total Storage

  • 10Public

    Additional Active Sites for NH3 Adsorption on Cu-SSZ-13In addition to the Strong-H and Weak-H sites, two additional sites considered for NH3 adsorption:

    Copper Sites (Temkin isotherm model)

    Physisorbed NH3 (to account for increased storage at high feeds and low temperatures. Langmuir

    isotherm model)

    π‘Ÿπ‘βˆ’πΆπ‘’ = π‘˜π‘βˆ’πΆπ‘’πœƒπΆπ‘’.𝑁𝐻3𝛺𝐢𝑒.𝑁𝐻3

    𝑁𝐻3 + 𝐢𝑒 β‡Ώ 𝐢𝑒.𝑁𝐻3π‘Ÿπ‘“βˆ’πΆπ‘’ = π‘˜π‘“βˆ’πΆπ‘’π‘¦π‘π»3πœƒπΆπ‘’π›ΊπΆπ‘’.𝑁𝐻3

    π‘Ÿπ‘βˆ’π‘ƒ = π‘˜π‘βˆ’π‘ƒπœƒπ‘ƒ.𝑁𝐻3𝛺𝑃

    𝑁𝐻3 + 𝑃 β‡Ώ 𝑃.𝑁𝐻3π‘Ÿπ‘“βˆ’π‘ƒ = π‘˜π‘“βˆ’π‘ƒπ‘¦π‘π»3πœƒπ‘ƒπ›Ίπ‘ƒ

    ZCu, Z2Cu and ZCuOH sites lumped

    into global Copper site, due to

    inability of NH3-TPD to resolve

    individual copper sites

    Isolated Cu2+ positions from AIMD [6]

    [6] Paolucci, C., Di Iorio, J. R., Ribeiro, F. H., Gounder, R., & Schneider, W. F. (2016). Catalysis science of NOx selective catalytic

    reduction with ammonia over Cu-SSZ-13 and Cu-SAPO-34. In Advances in Catalysis (Vol. 59, pp. 1-107). Academic Press.

  • 11Public

    Copper and Physisorbed Site Kinetics on Cu-SSZ-13

    β–ͺ NH3-TPD at 750Β°C-4h shows a primary release feature at 290Β°C, with a minor shoulder at 400Β°C

    β–ͺ Significant low temperature isothermal desorption attributed to a global physisorbed site. Isothermally

    desorbed NH3 shows non-monotonic trend with increased temperature

    Age : 600Β°C-2h

    Experiment : 1h isothermal

    adsorption followed by 40

    minutes isothermal desorption

  • 12Public

    Site-Specific Adsorption-Desorption Dynamicsβ–ͺ Quantitative predictions of the influence of catalyst temperature on storage of individual sites

    β–ͺ Steady-state total storage on 750Β°C-4h aged Cu-SSZ-13 compares well with model predictions

    Age : 600Β°C-2h

    Experiment : 1h isothermal

    adsorption followed by 40

    minutes isothermal desorption

  • 13Public

    NH3 Adsorption Equilibrium Thermodynamics

    [7] Paolucci, C., Parekh, A. A., Khurana, I., Di Iorio, J. R., Li, H., Albarracin Caballero, J. D., ... & Ribeiro, F. H.

    (2016). Catalysis in a cage: condition-dependent speciation and dynamics of exchanged Cu cations in SSZ-13

    zeolites. Journal of the American Chemical Society, 138(18), 6028-6048.

    β–ͺ Estimated adsorption enthalpies and entropic penalties are aligned with DFT/AIMD predicted values in

    literature

    β–ͺ Entropic penalties in line with the notion of mobile NH3 complexes on zeolite surface

    [5] Li, S., Zheng, Y., Gao, F., Szanyi, J., & Schneider, W. F. (2017). Experimental and computational interrogation of fast SCR

    mechanism and active sites on H-Form SSZ-13. ACS Catalysis, 7(8), 5087-5096.

    Model ParametersRecent DFT/AIMD Predictions [5, 7-8]

    [8] Li, H., Paolucci, C., & Schneider, W. F. (2018). Zeolite adsorption free energies from ab initio

    potentials of mean force. Journal of chemical theory and computation, 14(2), 929-938.

  • 14Public

    Modeling the change in NH3-TPD with hydrothermal

    agingβ–ͺ NH3-TPD experiments indicate a monotonic decrease in high temperature peak and increase in low

    temperature peak with increased aging [9]

    β–ͺ This behavior was modeled with:

    a) Fixed turnover rates (identified previously)

    b) Increased NH3 storage ability on Copper sites with aging

    c) Decreased number density of BrΓΈnsted acid sites with aging

    [9] Luo, J., Gao, F., Kamasamudram, K., Currier, N., Peden, C. H., & Yezerets, A.

    (2017). New insights into Cu/SSZ-13 SCR catalyst acidity. Part I: Nature of acidic

    sites probed by NH 3 titration. Journal of Catalysis, 348, 291-299.

  • 15Public

    Tracking Storage Capacity on Copper Sites and

    Number Density of BrΓΈnsted Acid Sitesβ–ͺ Increase in NH3 storage on copper sites is linearly related to the loss of BrΓΈnsted acid sites

    β–ͺ The loss of BrΓΈnsted acid sites with aging is used to develop a constitutive relationship for the

    evolution of these sites, yielding the hydrothermal aging equation

    NH3 Storage Ability on

    Copper Sites

    Number Density of

    BrΓΈnsted acid Sites

  • 16Public

    Hydrothermal Aging Equation

    𝟏

    πœ΄π‘―π’π’π’“π’Ž= 𝟐. πŸ“πŸ‘ βˆ— πŸπŸŽπŸ–π’†π’™π’‘ βˆ’

    πŸπŸ”πŸ–πŸ•πŸ‘πŸ‘

    π‘Ήπ‘»π’‚π’ˆπ’†π’•π’‚π’ˆπ’† + 𝟏

    Ratio-based calculator reported previously [10] Identical deactivation energies from two

    different derivation methods

    β–ͺ A linear relationship is found between the inverse BrΓΈnsted acid site density and aging time,

    implying a second order Arrhenius rate. The rate constant and activation energy are derived

    Arrhenius Plot

    [10] Luo, J., Kamasamudram, K., Currier, N., & Yezerets, A. (2018). NH3-TPD methodology for quantifying

    hydrothermal aging of Cu/SSZ-13 SCR catalysts. Chemical Engineering Science, 190, 60-67.

  • 17Public

    Model Limitations – Copper Site Deconvolution

    β–ͺ NH3 adsorption at 200Β°C leads to replacement of approximately two framework oxygen atoms on

    Z2Cu sites and approximately one framework oxygen atom on ZCuOH sites [9]

    𝜴π‘ͺ𝒖.π‘΅π‘―πŸ‘ = πŸπœ΄π’πŸπ‘ͺ𝒖′ + πŸπœ΄π’π‘ͺ𝒖𝑢𝑯

    β€²

    πœ΄π’π‘ͺ𝒖𝑢𝑯′

    πœ΄π’πŸπ‘ͺ𝒖′ + πœ΄π’π‘ͺ𝒖𝑢𝑯

    β€² = 𝟎. πŸ–πŸ• 𝒂𝒕 πŸ“πŸ“πŸŽΒ°π‘ͺ βˆ’ πŸ’π’‰π’…πœ΄π’πŸπ‘ͺ𝒖

    β€²

    π’…π’•π’‚π’ˆπ’†= βˆ’

    π’…πœ΄π’π‘ͺ𝒖𝑢𝑯′

    π’…π’•π’‚π’ˆπ’†

    βˆ’π’…πœ΄π‘―

    π’…π’•π’‚π’ˆπ’†= βˆ’

    π’…πœ΄π’π‘ͺ𝒖𝑢𝑯′

    π’…π’•π’‚π’ˆπ’†+ 𝟎. πŸ‘πŸ

    π’…πœ΄π’πŸπ‘ͺ𝒖′

    π’…π’•π’‚π’ˆπ’†

    Known from NH3-TPD model

    β–ͺ Model does not explicitly predict the evolution of individual Copper sites with hydrothermal aging.

    However, combining model results with other characterization and experimental data can provide

    some insight

    Reducible Cu2+ densities

    β–ͺ Additional characterization data on same catalyst :

    H2-TPR on degreened catalyst [9]

    β–ͺ Correlating BrΓΈnsted acid site loss rate with

    individual copper site change rate :

    NO + NH3 titration

    experiments

    [9] Luo, J., Gao, F., Kamasamudram, K., Currier, N., Peden, C. H., & Yezerets, A.

    (2017). New insights into Cu/SSZ-13 SCR catalyst acidity. Part I: Nature of acidic

    sites probed by NH 3 titration. Journal of Catalysis, 348, 291-299.

  • 18Public

    Summary and Future Workβ–ͺ Modeling of SCR catalyst aging is necessary to meet the next phase of tailpipe regulations and

    durability requirements

    β–ͺ If successfully developed and integrated with performance predictions, these models have

    significant applications in improved understanding and design of SCR catalysts, along with better

    catalyst health monitoring and control

    β–ͺ These models can be enabled by intrinsic micro-kinetics for species conversion on each active site

    and experimental quantification of active site evolution with aging. For instance, the loss of

    BrΓΈnsted acid sites with hydrothermal aging can be expressed by :

    β–ͺ Constitutive relations must be discovered for the response of all chemically distinct active sites to

    different SCR degradation mechanisms

    β–ͺ Once the catalyst state is known, the performance can be estimated using site-specific turnover

    rates identified through experimental and theoretical understanding

    𝟏

    πœ΄π‘―π’π’π’“π’Ž= 𝟐. πŸ“πŸ‘ βˆ— πŸπŸŽπŸ–π’†π’™π’‘ βˆ’

    πŸπŸ”πŸ–πŸ•πŸ‘πŸ‘

    π‘Ήπ‘»π’‚π’ˆπ’†π’•π’‚π’ˆπ’† + 𝟏

  • 1919

  • 20

    Backup Slides

    Public

  • 21Public

    Transient and Steady-State Coverages on H-SSZ-13β–ͺ The surface coverages are plotted as a function of time (transient TPD) and temperature (steady-state).

    Steady-state coverages compare qualitatively well with computational results in [5]

    [5] Li, S., Zheng, Y., Gao, F., Szanyi, J., & Schneider, W. F. (2017). Experimental and computational interrogation of fast SCR

    mechanism and active sites on H-Form SSZ-13. ACS Catalysis, 7(8), 5087-5096.

    Surface Coverages in [5]

    550Β°C-4h H-SSZ-13 NH3 TPD550Β°C-4h H-SSZ-13 Total Storage

  • 22Public

    Experimental Data : Jinyong Luo

    Transient and Steady-State Coverages on Cu-SSZ-13β–ͺ The surface coverages are plotted as a function of time (transient TPD) and temperature (steady-state)

  • 23Public

    Validation of modeling approach with steady-state

    Storage measurementsβ–ͺ Evolution of total NH3 storage with hydrothermal aging can be understood using the model

    β–ͺ With hydrothermal aging, the significance of BrΓΈnsted acid sites as a reservoirs of NH3 decreases

    Surprising experimental result at 450Β°C being

    investigated further

  • 24Public

    Analytical Expressions for Total and Site Specific Storageβ–ͺ The equilibrium constants on each site can be utilized to calculate site specific surface coverage using

    Langmuir’s adsorption isotherm

    πΏπ‘Žπ‘›π‘”π‘šπ‘’π‘–π‘Ÿ/π‘‡π‘’π‘šπ‘˜π‘–π‘› π‘†π‘’π‘Ÿπ‘“π‘Žπ‘π‘’ πΆπ‘œπ‘£π‘’π‘Ÿπ‘Žπ‘”π‘’ βˆ’β†’ πœ½π‘¬π’’π’Š(π’šπ‘΅π‘―πŸ‘ , 𝑻) =π‘²π‘¬π’’π’Šπ’šπ‘΅π‘―πŸ‘

    𝟏+π‘²π‘¬π’’π’Šπ’šπ‘΅π‘―πŸ‘π‘– = 𝐢𝑒 𝑠𝑖𝑑𝑒𝑠, π‘ƒβ„Žπ‘¦π‘  𝑠𝑖𝑑𝑒𝑠

    β–ͺ Once the surface coverage on each of the sites is known, the total ammonia storage can be calculated as

    follows:

    πŽπ‘΅π‘―πŸ‘ = π‘΄π‘Ύπ‘΅π‘―πŸ‘π‘Ύπ‘³

    π†π’˜πœ΄π‘ͺ𝒖.π‘΅π‘―πŸ‘πœ½π‘¬π’’π‘ͺ𝒖 + πœ΄π‘― πœ½π‘¬π’’π’π‘΅π‘―πŸ’

    + πŸπœ½π‘¬π’’π’π‘΅π‘―πŸ’π‘΅π‘―πŸ‘+ πœ΄π’‘πœ½π‘¬π’’π‘·

    Where πŽπ‘΅π‘―πŸ‘ is the NH3 storage in g/Lcat, π‘΄π‘Ύπ‘΅π‘―πŸ‘ is the molecular weight of NH3 in kg/mol, 𝑾𝑳 is washcoat loading in

    g/Lcat, π†π’˜ is washcoat density in kg/m3 (666 for DW3136 family), πœ΄π’Š mol/m

    3washcoat and πœ½π‘¬π’’π’Š is the equilibrium surface

    coverage of active site 𝑖

    β–ͺ In order to estimate NH3 storage as a function of aging time and temperature, πœ΄π’Š as a function of aging time and temperature must be calculated, and this is the objective of the aging model

    𝐡𝐸𝑇 π‘†π‘’π‘Ÿπ‘“π‘Žπ‘π‘’ πΆπ‘œπ‘£π‘’π‘Ÿπ‘Žπ‘”π‘’ βˆ’β†’ πœ½π‘¬π’’π’π‘΅π‘―πŸ’(π’šπ‘΅π‘―πŸ‘ , 𝑻) =π‘²π‘¬π’’π‘Ίπ‘―π’šπ‘΅π‘―πŸ‘

    𝟏+π‘²π‘¬π’’π‘Ίπ‘―π’šπ‘΅π‘―πŸ‘+π‘²π‘¬π’’π‘Ίπ‘―π‘²π‘¬π’’π‘Ύπ‘―π’šπ‘΅π‘―πŸ‘πŸ ; πœ½π‘¬π’’π’π‘΅π‘―πŸ’π‘΅π‘―πŸ‘(π’šπ‘΅π‘―πŸ‘ , 𝑻) =

    π‘²π‘¬π’’π‘Ίπ‘―π‘²π‘¬π’’π‘Ύπ‘―π’šπ‘΅π‘―πŸ‘πŸ

    𝟏+π‘²π‘¬π’’π‘Ίπ‘―π’šπ‘΅π‘―πŸ‘+π‘²π‘¬π’’π‘Ίπ‘―π‘²π‘¬π’’π‘Ύπ‘―π’šπ‘΅π‘―πŸ‘πŸ

  • 25Public

    Model Limitations – Severe Hydrothermal Aging

    β–ͺ Beyond a threshold aging, there is a change in

    NH3 storage energetics on Copper sites,

    characterized by a shift in the low temperature

    release peak from 290Β°C to 265Β°C

    β–ͺ Systematic analysis of NH3 TPD profile shows

    that are at least two different phases of

    hydrothermal aging:

    Phase I – Drop in ratio of high to low temperature

    peaks, but negligible loss of Cu2+ (transformation of

    ZCuOH to Z2Cu)

    Phase II – Drop in Cu2+ sites. BrΓΈnsted acid sites

    negligible. Change in energetics of low temperature

    sites. Loss of NH3 storage

  • 26Public

    Cu2+ site Distribution as a function of Hydrothermal

    Age

    Key Model Prediction : In the

    degreened state, 30-35% of the

    Copper does not store NH3, and

    must therefore not exist as

    isolated Cu2+

    𝑍2𝐢𝑒 𝑀𝑑.% =𝛺𝑍

    2𝐢𝑒 βˆ— π‘€π‘ŠπΆπ‘’ βˆ— π‘‰π‘Ÿπ·πΊ βˆ— 610.237

    𝑍𝐢𝑒𝑂𝐻 𝑀𝑑.% =𝛺𝑍𝐢𝑒𝑂𝐻 βˆ— π‘€π‘ŠπΆπ‘’ βˆ— π‘‰π‘Ÿ

    𝐷𝐺 βˆ— 610.237

    Where π‘€π‘ŠπΆπ‘’ is the molecular weight of Cu in

    g/mol, π‘‰π‘Ÿ is ratio of washcoatvolume to reactor volume

    and 𝐷𝐺 is dry gain in g/in3


Recommended