Development and Validation of a multi-site kinetic model for NH3-SCR over Cu-SSZ-13

Rohil DayaIsuzu Technical Center of America

10/5/2017 2

Introduction, Objective and Purpose➢ Cu-CHA small pore SCR catalysts utilized worldwide due to increased range of temperature for high DeNOx, along with good hydrothermal stability

➢ Due to the relatively simple structure of SSZ-13, it has been investigated intensively by researchers (DeNOx DOE Team, Schneider Group at U-Notre Dame, Gounder group at Purdue etc.)

➢ However, limited global models of Cu-SSZ-13 exist in literature, and the ones that do are not complete in terms of described operating conditions (e.g. [1-2])

Structure of SSZ-13 [3]

[1] Stewart et al. (2013) Global Kinetic SCR model with Two Ammonia Storage Sites. CLEERS 2013

[2] Olsson, L., Wijayanti, K., Leistner, K., Kumar, A., Joshi, S. Y., Kamasamudram, K., ... & Yezerets, A. (2015).

A multi-site kinetic model for NH 3-SCR over Cu/SSZ-13. Applied Catalysis B: Environmental, 174, 212-224.

[3] Gounder et al. (2016) New insights into the mechanisms and Active Site requirements of Low Temperature

NOx SCR with Ammonia on Cu-SSZ-13 zeolites. CLEERS 2016

Objective

➢ Develop a complete kinetic model for ammonia SCR over Cu-SSZ-13 in a temperature interval of 150-550°C for 2 space velocities and 2 thermal ageing

conditions

Purpose

➢ Model-based Urea Dosing Calibration and Control

➢ Feasibility studies for hardware modifications

10/5/2017 3

Experimental Setup

➢ Catalyst procured from supplier

➢ Square core-section cut, keeping length identical to full scale (h = 15 mm, l = 190 mm)

➢ 3 instruments used for transient concentration measurements, along with outlet N2 measurements

Inlet & Outlet : MKS Instruments 2030 FTIR Continuous Gas Analyzer

Outlet : Hiden Analytical HPR-20 MS QGA

Mass Flow

Controllers

ExhaustFlow Meter Preheater

Water Pump

Outlet Temp

Control Loop

Gas

Cylinders

MS_QGA

Furnace

SCR

Sample

FTIR

FTIRTC1 TC3

TC2

10/5/2017 4

Synthetic Gas Bench (SGB) Protocol

➢ Internally developed SCR protocol used for reactor testing. Notable aspects:

1. 0.2% O2 used in NH3 Temperature Programmed Desorption (TPD) test (not shown here) based on [4]

2. Cleaning Step post NH3 storage/oxidation

3. Separate sequence for NO2 SCR (not shown here) between 225-550°C

4. Two Standard SVs (30k/h and 60k/h) and two ageing conditions:

Degreening 650°C for 16 hours

Ageing 700°C for 100 hours

5. No consideration of sulfur poisoning (future step)

[4] Pihl et al. (2015) Measuring the impacts of catalyst state on NH3 adsorption in Copper zeolite SCR catalysts. CLEERS 2013

NH3 Storage/

Oxidation

NH3 Inventory

and NO

Oxidation

NO SCRNO + NO2

SCR

Protocol used from 250-550°C

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Synthetic Gas Bench (SGB) Protocol

➢ 4.5% H2O and 5% CO2 used in all steps

NH3 Storage/

Oxidation

NH3 Inventory

and NO

Oxidation

NO SCRNO + NO2

SCR

Protocol used from 250-550°C

Step Mole Fraction Concentrations

NH3 Storage 300 ppm NH3, 0.2% O2

NH3 Oxidation 300 ppm NH3, 10% O2

NH3 Inventory 300 ppm NO, 10% O2

NO Oxidation 200 ppm NO, 100 ppm NO2, 10% O2

NO SCR 300 ppm NH3, 300 ppm NO, 10% O2

NO + NO2 SCR 300 ppm NH3, 150 ppm NO, 150 ppm NO2, 10% O2

NO2-SCR 300 ppm NH3, 225 ppm NO2, 10% O2

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Modeling Approach governed by TPD data

Temperature (°C) NH3 Concentration (ppm)

Catalyst Ageing

and SV (1/h)

Low T Site

Desorption Peak

High T Site

Desorption Peak

Low T Site Desorption

Peak at 150 C

High T Site Desorption

Peak at 150 C

Degreened 30k 330 440 230 105

Aged 30k 310 n/a 280 n/a

Low T Site High T Site

Low T Site

➢ Ageing led to migration of High T Site to Low T

➢ NH3 Oxidation insignificant below 400°C, but interferes with High T site peak

➢ Low T & High T Site named as placeholders

➢ Nature of sites will be discussed post NH3 storage model construction

Desorption Peaks in NH3 TPD test

10/5/2017 7

Modeling Setup and Assumptions

➢ 1+1D model developed using GT-Suite v2017

➢ Two-site adsorption-reaction model used, with Eley-Rideal kinetics and Temkin type adsorption on Low T Site

Key Modeling Assumptions

➢ Fully developed laminar flow

➢ Entire substrate represented with a single channel (transverse gradients in solid temperature neglected)

➢ Gas-phase diffusion modeled using “film” approach with transfer coefficients

➢ Uniform washcoat loading

➢ Global Reaction Kinetics

➢ Washcoat pore diffusion accounted for using asymptotic approach [5]

➢ Porosity and tortuosity values modified to match effective diffusivities in [6]

[5] Bissett, E. J. (2015). An asymptotic solution for washcoat pore diffusion in catalytic monoliths. Emission Control Science and Technology, 1(1), 3-16.

[6] Metkar, P. S., Harold, M. P., & Balakotaiah, V. (2013). Experimental and kinetic modeling study of NH 3-SCR of NOx on Fe-ZSM-5, Cu-chabazite and

combined Fe-and Cu-zeolite monolithic catalysts. Chemical engineering science, 87, 51-66.

10/5/2017 8

SCR Modeling in GT-Suite – EquationsKey Conservation Equations (Quasi-Steady) [7]

Gas Phase Continuity :

Species Mass Balance:

Washcoat Diffusion:

Note: See Appendix for nomenclature

[7] GT-Suite Exhaust Aftertreatment Application Manual v2017 Kinetic Model Setup in GT-Suite v2017

10/5/2017 9

NH3 Storage Model – Results at SV:30k/h and T=150°C

𝜴𝟏

𝟎.𝟓𝟏+ 𝜴𝟐= const.

➢ Site 1 density reduced by 90%

while Site 2 density increased by

40% upon ageing

➢ Same kinetic constants used for degreened and aged SCR

In [1], this value for

the storage model was 0.92

𝑁𝐻3+ 𝑆1 𝑁𝐻3− 𝑆1

𝑁𝐻3+ 𝑆2 𝑁𝐻3− 𝑆2

D/A-30/60 Degreened/Aged at Standard SV: 30/60 k/h

[1] Stewart et al. (2013) Global Kinetic SCR model

with Two Ammonia Storage Sites. CLEERS 2013

10/5/2017 10

NH3 Storage Model – Nature of Active Sites➢ Final storage model analyzed, and “assigned” physical significance

What is known about these sites?

➢ [8] show two chemically distinct active monomer sites, with Z2Cu type monomer dominant for low ion-exchange levels

➢ [9] argue that low temperature NH3 oxidation sites are dimers, and they exist for low Cu loadings too

➢ [10] show NH3 oxidation and NO oxidation is only catalyzed over ZCuOH sites, which are likely located near the 8MR CHA-cages

Cu monomer site fraction as a

function of Cu/Al and Si/Al ratios [8]

➢ [11] use DRIFTS and H2-TPR to show that low temperature TPD peak is due to Cu sites, and high temperature peak is due to Bronsted sites

➢ Furthermore, [11] argue that deactivation of Bronsted sites upon hydrothermal ageing is through transformation of Cu sites:

ZCuOH + ZH = Z2Cu + H2O

[8] Schneider et al. (2015) Sites and Mechanisms for NOx transformations in Cu-SSZ-13. CLEERS 2015

[9] Gao, F., Walter, E. D., Kollar, M., Wang, Y., Szanyi, J., & Peden, C. H. (2014). Understanding ammonia selective catalytic

reduction kinetics over Cu/SSZ-13 from motion of the Cu ions. Journal of Catalysis, 319, 1-14.

[10] Luo, J., Wang, D., Kumar, A., Li, J., Kamasamudram, K., Currier, N., & Yezerets, A. (2016). Identification of two types of Cu sites

in Cu/SSZ-13 and their unique responses to hydrothermal aging and sulfur poisoning. Catalysis Today, 267, 3-9.

[11] 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.

10/5/2017 11

NH3 Storage Model – Nature of Active Sites

TPD Observations (Simulation)

➢ Low T physisorbed NH3 desorbed from S2

➢ Low T chemisorbed NH3 desorbed from S2, which increased with ageing

➢ High T chemisorbed NH3 desorbed from S1, which decreased with ageing

Deduced Site Definitions (Lumped)

S1 : ZCuOH sites in CHA cages and Bronsted sites, along with transient low temperature Cu dimers (if any)

S2 : Z2Cu sites in 6MR and Physisorbed NH3 sites

D/A-30/60 Degreened/Aged at Standard SV: 30/60 k/h

10/5/2017 12

NH3 Oxidation Model – Results at SV:30k/h

4𝑁𝐻3− 𝑆1 + 3𝑂2 → 2𝑁2+ 6𝐻2𝑂 + 4𝑆1

4𝑁𝐻3− 𝑆1 + 5𝑂2 → 4𝑁𝑂 + 6𝐻2𝑂 + 4𝑆1

4𝑁𝐻3− 𝑆2 + 5𝑂2 → 4𝑁𝑂 + 6𝐻2𝑂 + 4𝑆2

➢ Aging led to reduced oxidation (as would be expected if catalyzed by ZCuOH sites)

➢ NH3 storage data at 0.2% O2, along with oxidation data at 10% O2, allows for determination of O2 reaction order

➢ Calibrated value ~ 0.5

D/A-30/60 Degreened/Aged at Standard SV: 30/60 k/h

2𝑁𝐻3− 𝑆2 + 2𝑂2 → 𝑁2𝑂 + 3𝐻2𝑂 + 2𝑆2

10/5/2017 13

NO Oxidation Model - Results at SV:30k/h

𝑁𝑂 + 0.5𝑂2 𝑁𝑂2

➢ Reaction rate only dependent on S1 site density (ZCuOH sites lumped in S1)

D/A-30/60 Degreened/Aged at Standard SV: 30/60 k/h

10/5/2017 14

Standard SCR Model – Results at SV:30k/h

4𝑁𝐻3− 𝑆1 + 4𝑁𝑂 + 𝑂2 → 4𝑁2+ 6𝐻2𝑂 + 4𝑆1

4𝑁𝐻3− 𝑆2 + 4𝑁𝑂 + 𝑂2 → 4𝑁2+ 6𝐻2𝑂 + 4𝑆2

➢ Significant over-prediction in NOx

conversion at 150°C

➢ In general, reactions proceed on both sites, with different activation energies

D/A-30/60 Degreened/Aged at Standard SV: 30/60 k/h

2𝑁𝐻3− 𝑆1 + 2𝑁𝑂 + 𝑂2 → 𝑁2+ 𝑁2𝑂 + 6𝐻2𝑂 + 4𝑆1

2𝑁𝐻3− 𝑆2 + 2𝑁𝑂 + 𝑂2 → 𝑁2+ 𝑁2𝑂 + 6𝐻2𝑂 + 4𝑆2

10/5/2017 15

Standard SCR Model Validation – ANR 1.24𝑁𝐻3− 𝑆1 + 4𝑁𝑂 + 𝑂2 → 4𝑁2+ 6𝐻2𝑂 + 4𝑆1 4𝑁𝐻3− 𝑆2 + 4𝑁𝑂 + 𝑂2 → 4𝑁2+ 6𝐻2𝑂 + 4𝑆2

D/A-30/60 Degreened/Aged at Standard SV: 30/60 k/h

10/5/2017 16

➢ Clear hysteresis in the N2O curves

below 300°C

➢ A global N2O formation model, such as

the one represented by the equation

below, will NOT capture this hysteresis

effect

2NH3-S + 2NO2 N2 + N2O + 3H2O +2S

NO2 SCR Data – Nitrate Hysteresis

Cooling

Heating

D/A-30/60 Degreened/Aged at Standard SV: 30/60 k/h

Inlet Feedgas and Temperature Profiles

10/5/2017 17

NO2 SCR Model – Results at SV:30k/h

8𝑁𝐻3− 𝑆1 + 6𝑁𝑂2 → 7𝑁2+ 12𝐻2𝑂 + 8𝑆1

8𝑁𝐻3− 𝑆2 + 6𝑁𝑂2 → 7𝑁2+ 12𝐻2𝑂 + 8𝑆2

➢ Over-prediction in NH3 conversion below 400°C

➢ In general, reactions proceed on both sites, with different activation energies

➢ N2O slip model captured overall trend, but needs improvement

D/A-30/60 Degreened/Aged at Standard SV: 30/60 k/h

2𝑁𝐻3− 𝑆1 + 2𝑁𝑂2 → 𝑁2+ 𝑁𝐻4𝑁𝑂3− 𝑆1 + 𝐻2𝑂 + 𝑆1

2𝑁𝐻3− 𝑆2 + 2𝑁𝑂2 → 𝑁2+ 𝑁𝐻4𝑁𝑂3− 𝑆2 + 𝐻2𝑂 + 𝑆2

𝑁𝐻4𝑁𝑂3− 𝑆1 → 𝑁2𝑂 + 2𝐻2𝑂 + 𝑆1

𝑁𝐻4𝑁𝑂3− 𝑆2 → 𝑁2𝑂 + 2𝐻2𝑂 + 𝑆2

10/5/2017 18

NO2 SCR Model – N2O Hysteresis Result at SV: 30k/h

➢ N2O slip model captures overall trend, but needs improvement

D/A-30/60 Degreened/Aged at Standard SV: 30/60 k/h

2𝑁𝐻3− 𝑆1 + 2𝑁𝑂2 → 𝑁2+ 𝑁𝐻4𝑁𝑂3− 𝑆1 + 𝐻2𝑂 + 𝑆1

2𝑁𝐻3− 𝑆2 + 2𝑁𝑂2 → 𝑁2+ 𝑁𝐻4𝑁𝑂3− 𝑆2 + 𝐻2𝑂 + 𝑆2

𝑁𝐻4𝑁𝑂3− 𝑆1 → 𝑁2𝑂 + 2𝐻2𝑂 + 𝑆1

𝑁𝐻4𝑁𝑂3− 𝑆2 → 𝑁2𝑂 + 2𝐻2𝑂 + 𝑆2

Method 2

2𝑁𝐻3− 𝑆1 + 2𝑁𝑂2 → 𝑁2+ 𝑁2𝑂 + 3𝐻2𝑂 + 2𝑆1

2𝑁𝐻3− 𝑆2 + 2𝑁𝑂2 → 𝑁2+ 𝑁2𝑂 + 3𝐻2𝑂 + 2𝑆2

Method 1

10/5/2017 19

Fast SCR Data – Nitrate Hysteresis➢ This hysteresis in N2O yield is

replicated by N2

➢ This implies hysteresis in NO

conversion, as reported by [12]

Cooling

Heating

[12] Gao, Feng, et al. "A comparative kinetics study between Cu/SSZ-13

and Fe/SSZ-13 SCR catalysts." Catalysis Today 258 (2015): 347-358.

NO Conversion Hysteresis [12]

D/A-30/60 Degreened/Aged at Standard SV: 30/60 k/h

Cooling

Heating

10/5/2017 20

Example Engine-Dyno Validation Case – ANR Sweep at 350°C, NO2/NOx = 0.29 and SV: 11,000/h

Note :

Fast SCR Model still under development

Latest kinetics used for results

demonstration

10/5/2017 21

Summary and Future Work

➢ A multi-site kinetic model has been developed to describe the behavior of Cu-SSZ-13 for NH3 SCR over all operating ranges of temperature, space velocity and catalyst hydrothermal ageing

➢ The model successfully described active site migration upon hydrothermal ageing, and the corresponding change in storage behavior

➢ Oxidation behaviors were described accurately, including NO formation from NH3 oxidation

➢ Reduction functionality of the SCR was described reasonably well, however NO2 related SCR chemistry needs improvement

Future Work

➢ Complete Fast SCR model development

➢ Improve N2O slip prediction (& correspondingly NOx prediction)

➢ Comprehensive validation with steady-state and transient engine dynamometer data

➢ Utilize model to assist in Urea-dosing calibration development

➢ Model Application Analyze Washcoat Gradients, Dynamic Capacity, Axial NH3 and NOx profiles

➢ Add H2O Storage model

➢ Understand and model influence of sulfur poisoning

10/5/2017 22

Acknowledgments

➢ Cormetech Inc. for executing test protocol and supplying reactor data

➢ Gamma Technologies Aftertreatment Team (Ryan Dudgeon, Jon Brown, Ed Bissett, Syed Wahiduzzaman) for support

➢ Chintan Desai and Kamal Choudhary for assistance in data collection and analysis

➢ Bruce Verham, Yasuo Fukai and Isuzu US team

10/5/2017 24

Appendix - Nomenclature

Back-Up Slides

10/5/2017 26

NH3 Storage Model – Results at SV:60k/h and T=150°C

[1] Stewart et al. (2013) Global Kinetic SCR model

with Two Ammonia Storage Sites. CLEERS 2013

𝑁𝐻3 + 𝑆1 𝑁𝐻3− 𝑆1

𝑁𝐻3 + 𝑆2 𝑁𝐻3− 𝑆2

D/A-30/60 Degreened/Aged at Standard SV: 30/60 k/h

𝜴𝟏

𝟎.𝟓𝟏+ 𝜴𝟐= const.

➢ Site 1 density reduced by 90%

while Site 2 density increased by

40% upon ageing

➢ Same kinetic constants used for degreened and aged SCR

In [1], this value for

the storage model was 0.92

10/5/2017 27

NH3 Oxidation Model – Results at SV:60k/h

4𝑁𝐻3− 𝑆1 + 3𝑂2 → 2𝑁2+ 6𝐻2𝑂 + 4𝑆1

4𝑁𝐻3− 𝑆1 + 5𝑂2 → 4𝑁𝑂 + 6𝐻2𝑂 + 4𝑆1

4𝑁𝐻3− 𝑆2 + 5𝑂2 → 4𝑁𝑂 + 6𝐻2𝑂 + 4𝑆2

➢ Aging leads to reduced oxidation (as would be expected if catalyzed by ZCuOH sites)

➢ NH3 storage data at 0.2% O2, along with oxidation data at 10% O2, allows for determination of O2 reaction order

➢ Calibrated value ~ 0.5

➢ Further ageing beyond 750°C will increase oxidation due to cluster formation

D/A-30/60 Degreened/Aged at Standard SV: 30/60 k/h

2𝑁𝐻3− 𝑆2 + 2𝑂2 → 𝑁2𝑂 + 3𝐻2𝑂 + 2𝑆2

10/5/2017 28

NO Oxidation Model - Results at SV:60k/h

𝑁𝑂 + 0.5𝑂2 𝑁𝑂2

➢ Reaction rate only dependent on S1 site density (ZCuOH sites lumped in S1)

D/A-30/60 Degreened/Aged at Standard SV: 30/60 k/h

10/5/2017 29

Standard SCR Model – Results at SV:60k/h

4𝑁𝐻3− 𝑆1 + 4𝑁𝑂 + 𝑂2 → 4𝑁2+ 6𝐻2𝑂 + 4𝑆1

4𝑁𝐻3− 𝑆2 + 4𝑁𝑂 + 𝑂2 → 4𝑁2+ 6𝐻2𝑂 + 4𝑆2

➢ Significant over-prediction in NOx

conversion at 150°C

➢ In general, reactions proceed on both sites, with different activation energies

D/A-30/60 Degreened/Aged at Standard SV: 30/60 k/h

2𝑁𝐻3− 𝑆1 + 2𝑁𝑂 + 𝑂2 → 𝑁2+ 𝑁2𝑂 + 6𝐻2𝑂 + 4𝑆1

2𝑁𝐻3− 𝑆2 + 2𝑁𝑂 + 𝑂2 → 𝑁2+ 𝑁2𝑂 + 6𝐻2𝑂 + 4𝑆2

10/5/2017 30

Standard SCR Model Validation – ANR 0.84𝑁𝐻3− 𝑆1 + 4𝑁𝑂 + 𝑂2 → 4𝑁2+ 6𝐻2𝑂 + 4𝑆1 4𝑁𝐻3− 𝑆2 + 4𝑁𝑂 + 𝑂2 → 4𝑁2+ 6𝐻2𝑂 + 4𝑆2

D/A-30/60 Degreened/Aged at Standard SV: 30/60 k/h

10/5/2017 31

NO2 SCR Model – Results at SV:60k/h

8𝑁𝐻3− 𝑆1 + 6𝑁𝑂2 → 7𝑁2+ 12𝐻2𝑂 + 8𝑆1

8𝑁𝐻3− 𝑆2 + 6𝑁𝑂2 → 7𝑁2+ 12𝐻2𝑂 + 8𝑆2

➢ Over-prediction in NOx conversion at 150°C

➢ In general, reactions proceed on both sites, with different activation energies

➢ N2O slip model captures overall trend, but needs improvement

D/A-30/60 Degreened/Aged at Standard SV: 30/60 k/h

2𝑁𝐻3− 𝑆1 + 2𝑁𝑂2 → 𝑁2+ 𝑁𝐻4𝑁𝑂3− 𝑆1 + 𝐻2𝑂 + 𝑆1

2𝑁𝐻3− 𝑆2 + 2𝑁𝑂2 → 𝑁2+ 𝑁𝐻4𝑁𝑂3− 𝑆2 + 𝐻2𝑂 + 𝑆2

𝑁𝐻4𝑁𝑂3− 𝑆1 → 𝑁2𝑂 + 2𝐻2𝑂 + 𝑆1

𝑁𝐻4𝑁𝑂3− 𝑆2 → 𝑁2𝑂 + 2𝐻2𝑂 + 𝑆2

10/5/2017 32

NO2 SCR Model – N2O Hysteresis Result at SV: 60k/h

➢ N2O slip model captures overall trend, but needs improvement

D/A-30/60 Degreened/Aged at Standard SV: 30/60 k/h

2𝑁𝐻3− 𝑆1 + 2𝑁𝑂2 → 𝑁2+ 𝑁𝐻4𝑁𝑂3− 𝑆1 + 𝐻2𝑂 + 𝑆1

2𝑁𝐻3− 𝑆2 + 2𝑁𝑂2 → 𝑁2+ 𝑁𝐻4𝑁𝑂3− 𝑆2 + 𝐻2𝑂 + 𝑆2

𝑁𝐻4𝑁𝑂3− 𝑆1 → 𝑁2𝑂 + 2𝐻2𝑂 + 𝑆1

𝑁𝐻4𝑁𝑂3− 𝑆2 → 𝑁2𝑂 + 2𝐻2𝑂 + 𝑆2

Method 2

2𝑁𝐻3− 𝑆1 + 2𝑁𝑂2 → 𝑁2+ 𝑁2𝑂 + 3𝐻2𝑂 + 2𝑆1

2𝑁𝐻3− 𝑆2 + 2𝑁𝑂2 → 𝑁2+ 𝑁2𝑂 + 3𝐻2𝑂 + 2𝑆2

Method 1

10/5/2017 33

Standard SCR Data – No Hysteresis➢ Comparing the data during steady

ramp down and transient ramp up

can give information related to

hysteresis

➢ More specifically, analysis of N2O

and N2 yields give information

related to nitrate formation, stability,

and impact on SCR efficiencies

➢ For standard SCR, identical N2O

curves obtained during ramp up and

ramp down indicating:

• Low N2O stabilization time during

ramp down

• No hysteresis for standard SCR