Development and Validation of a multi-site kinetic model for NH 3 -SCR over Cu-SSZ-13. Rohil Daya Isuzu Technical Center of America

Transcription

1 Development and Validation of a multi-site kinetic model for NH 3 -SCR over Cu-SSZ-13 Rohil Daya Isuzu Technical Center of America

2 Introduction, Objective and Purpose Cu-CHA small pore SCR catalysts utilized worldwide due to increased range of temperature for high DeNO x, along with good hydrothermal stability Due to the relatively simple structure of SSZ-13, it has been investigated intensively by researchers (DeNO x 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]) Objective Develop a complete kinetic model for ammonia SCR over Cu-SSZ-13 in a temperature interval of C for 2 space velocities and 2 thermal ageing conditions Purpose Model-based Urea Dosing Calibration and Control Feasibility studies for hardware modifications [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, [3] Gounder et al. (2016) New insights into the mechanisms and Active Site requirements of Low Temperature NO x SCR with Ammonia on Cu-SSZ-13 zeolites. CLEERS 2016 Structure of SSZ-13 [3] 10/5/2017 2

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 N 2 measurements Inlet & Outlet : MKS Instruments 2030 FTIR Continuous Gas Analyzer Outlet : Hiden Analytical HPR-20 MS QGA Mass Flow Controllers Flow Meter Water Pump Preheater FTIR TC2 Furnace MS_QGA Exhaust Gas Cylinders Outlet Temp Control Loop TC1 SCR Sample TC3 FTIR 10/5/2017 3

4 Internally developed SCR protocol used for reactor testing. Notable aspects: % O 2 used in NH 3 Temperature Programmed Desorption (TPD) test (not shown here) based on [4] 2. Cleaning Step post NH 3 storage/oxidation 3. Separate sequence for NO 2 SCR (not shown here) between 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) Synthetic Gas Bench (SGB) Protocol NH 3 Storage/ Oxidation NH 3 Inventory and NO Oxidation [4] Pihl et al. (2015) Measuring the impacts of catalyst state on NH 3 adsorption in Copper zeolite SCR catalysts. CLEERS 2013 NO SCR NO + NO 2 SCR Protocol used from C 10/5/2017 4

5 Synthetic Gas Bench (SGB) Protocol NH 3 Storage/ Oxidation NH 3 Inventory and NO Oxidation NO SCR NO + NO 2 SCR Step Mole Fraction Concentrations NH 3 Storage 300 ppm NH 3, 0.2% O 2 NH 3 Oxidation 300 ppm NH 3, 10% O 2 NH 3 Inventory 300 ppm NO, 10% O 2 NO Oxidation 200 ppm NO, 100 ppm NO 2, 10% O 2 NO SCR 300 ppm NH 3, 300 ppm NO, 10% O 2 NO + NO 2 SCR 300 ppm NH 3, 150 ppm NO, 150 ppm NO 2, 10% O 2 NO 2 -SCR 300 ppm NH 3, 225 ppm NO 2, 10% O 2 4.5% H 2 O and 5% CO 2 used in all steps Protocol used from C 10/5/2017 5

6 Ageing led to migration of High T Site to Low T NH 3 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 NH 3 storage model construction Modeling Approach governed by TPD data Low T Site Low T Site High T Site Desorption Peaks in NH 3 TPD test Temperature ( C) NH 3 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 Aged 30k 310 n/a 280 n/a 10/5/2017 6

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), [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, /5/2017 7

8 SCR Modeling in GT-Suite Equations Key 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 v /5/2017 8

9 NH 3 Storage Model Results at SV:30k/h and T=150 C NH 3 + S1 NH 3 + S2 NH 3 S1 NH 3 S2 Site 1 density reduced by 90% while Site 2 density increased by 40% upon ageing Same kinetic constants used for degreened and aged SCR Ω Ω 2 = const. In [1], this value for the storage model was 0.92 [1] Stewart et al. (2013) Global Kinetic SCR model with Two Ammonia Storage Sites. CLEERS /5/2017 9

10 NH 3 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 Z 2 Cu type monomer dominant for low ionexchange levels [9] argue that low temperature NH 3 oxidation sites are dimers, and they exist for low Cu loadings too [10] show NH 3 oxidation and NO oxidation is only catalyzed over ZCuOH sites, which are likely located near the 8MR CHA-cages [11] use DRIFTS and H 2 -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 = Z 2 Cu + H 2 O [8] Schneider et al. (2015) Sites and Mechanisms for NO x 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, [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, Cu monomer site fraction as a function of Cu/Al and Si/Al ratios [8] 10/5/

11 NH 3 Storage Model Nature of Active Sites TPD Observations (Simulation) Low T physisorbed NH 3 desorbed from S2 Low T chemisorbed NH 3 desorbed from S2, which increased with ageing High T chemisorbed NH 3 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 : Z 2 Cu sites in 6MR and Physisorbed NH 3 sites 10/5/

12 4NH 3 S1 + 3O 2 2N 2 + 6H 2 O + 4S1 2NH 3 S2 + 2O 2 N 2 O + 3H 2 O + 2S2 4NH 3 S1 + 5O 2 4NO + 6H 2 O + 4S1 4NH 3 S2 + 5O 2 4NO + 6H 2 O + 4S2 NH 3 Oxidation Model Results at SV:30k/h Aging led to reduced oxidation (as would be expected if catalyzed by ZCuOH sites) NH 3 storage data at 0.2% O 2, along with oxidation data at 10% O 2, allows for determination of O 2 reaction order Calibrated value ~ /5/

13 NO Oxidation Model - Results at SV:30k/h NO + 0.5O 2 NO 2 Reaction rate only dependent on S1 site density (ZCuOH sites lumped in S1) 10/5/

14 4NH 3 S1 + 4NO + O 2 4N 2 + 6H 2 O + 4S1 4NH 3 S2 + 4NO + O 2 4N 2 + 6H 2 O + 4S2 2NH 3 S1 + 2NO + O 2 N 2 + N 2 O + 6H 2 O + 4S1 2NH 3 S2 + 2NO + O 2 N 2 + N 2 O + 6H 2 O + 4S2 Standard SCR Model Results at SV:30k/h Significant over-prediction in NO x conversion at 150 C In general, reactions proceed on both sites, with different activation energies 10/5/

15 4NH 3 S1 + 4NO + O 2 4N 2 + 6H 2 O + 4S1 Standard SCR Model Validation ANR 1.2 4NH 3 S2 + 4NO + O 2 4N 2 + 6H 2 O + 4S2 10/5/

16 Inlet Feedgas and Temperature Profiles NO 2 SCR Data Nitrate Hysteresis Clear hysteresis in the N 2 O curves below 300 C A global N 2 O formation model, such as the one represented by the equation below, will NOT capture this hysteresis effect 2NH 3 -S + 2NO 2 N 2 + N 2 O + 3H 2 O +2S Cooling Heating 10/5/

17 8NH 3 S1 + 6NO 2 7N H 2 O + 8S1 8NH 3 S2 + 6NO 2 7N H 2 O + 8S2 2NH 3 S1 + 2NO 2 N 2 + NH 4 NO 3 S1 + H 2 O + S1 NH 4 NO 3 S1 N 2 O + 2H 2 O + S1 2NH 3 S2 + 2NO 2 N 2 + NH 4 NO 3 S2 + H 2 O + S2 NH 4 NO 3 S2 N 2 O + 2H 2 O + S2 NO 2 SCR Model Results at SV:30k/h Over-prediction in NH 3 conversion below 400 C In general, reactions proceed on both sites, with different activation energies N 2 O slip model captured overall trend, but needs improvement 10/5/

18 NO 2 SCR Model N 2 O Hysteresis Result at SV: 30k/h Method 1 2NH 3 S1 + 2NO 2 N 2 + N 2 O + 3H 2 O + 2S1 2NH 3 S2 + 2NO 2 N 2 + N 2 O + 3H 2 O + 2S2 Method 2 2NH 3 S1 + 2NO 2 N 2 + NH 4 NO 3 S1 + H 2 O + S1 NH 4 NO 3 S1 N 2 O + 2H 2 O + S1 2NH 3 S2 + 2NO 2 N 2 + NH 4 NO 3 S2 + H 2 O + S2 NH 4 NO 3 S2 N 2 O + 2H 2 O + S2 N 2 O slip model captures overall trend, but needs improvement 10/5/

19 Fast SCR Data Nitrate Hysteresis This hysteresis in N 2 O yield is replicated by N 2 This implies hysteresis in NO conversion, as reported by [12] Heating Cooling Cooling Heating NO Conversion Hysteresis [12] [12] Gao, Feng, et al. "A comparative kinetics study between Cu/SSZ-13 and Fe/SSZ-13 SCR catalysts." Catalysis Today 258 (2015): /5/

20 Example Engine-Dyno Validation Case ANR Sweep at 350 C, NO 2 /NO x = 0.29 and SV: 11,000/h Note : Fast SCR Model still under development Latest kinetics used for results demonstration 10/5/

21 Summary and Future Work A multi-site kinetic model has been developed to describe the behavior of Cu-SSZ-13 for NH 3 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 NH 3 oxidation Reduction functionality of the SCR was described reasonably well, however NO 2 related SCR chemistry needs improvement Future Work Complete Fast SCR model development Improve N 2 O slip prediction (& correspondingly NO x 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 NH 3 and NO x profiles Add H 2 O Storage model Understand and model influence of sulfur poisoning 10/5/

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/

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24 Appendix - Nomenclature 10/5/

25 Back-Up Slides

26 NH 3 Storage Model Results at SV:60k/h and T=150 C NH 3 + S1 NH 3 + S2 NH 3 S1 NH 3 S2 Site 1 density reduced by 90% while Site 2 density increased by 40% upon ageing Same kinetic constants used for degreened and aged SCR Ω Ω 2 = const. In [1], this value for the storage model was 0.92 [1] Stewart et al. (2013) Global Kinetic SCR model with Two Ammonia Storage Sites. CLEERS /5/

27 4NH 3 S1 + 3O 2 2N 2 + 6H 2 O + 4S1 2NH 3 S2 + 2O 2 N 2 O + 3H 2 O + 2S2 4NH 3 S1 + 5O 2 4NO + 6H 2 O + 4S1 4NH 3 S2 + 5O 2 4NO + 6H 2 O + 4S2 NH 3 Oxidation Model Results at SV:60k/h Aging leads to reduced oxidation (as would be expected if catalyzed by ZCuOH sites) NH 3 storage data at 0.2% O 2, along with oxidation data at 10% O 2, allows for determination of O 2 reaction order Calibrated value ~ 0.5 Further ageing beyond 750 C will increase oxidation due to cluster formation 10/5/

28 NO Oxidation Model - Results at SV:60k/h NO + 0.5O 2 NO 2 Reaction rate only dependent on S1 site density (ZCuOH sites lumped in S1) 10/5/

29 4NH 3 S1 + 4NO + O 2 4N 2 + 6H 2 O + 4S1 4NH 3 S2 + 4NO + O 2 4N 2 + 6H 2 O + 4S2 2NH 3 S1 + 2NO + O 2 N 2 + N 2 O + 6H 2 O + 4S1 2NH 3 S2 + 2NO + O 2 N 2 + N 2 O + 6H 2 O + 4S2 Standard SCR Model Results at SV:60k/h Significant over-prediction in NO x conversion at 150 C In general, reactions proceed on both sites, with different activation energies 10/5/

30 Standard SCR Model Validation ANR 0.8 4NH 3 S1 + 4NO + O 2 4N 2 + 6H 2 O + 4S1 4NH 3 S2 + 4NO + O 2 4N 2 + 6H 2 O + 4S2 10/5/

31 8NH 3 S1 + 6NO 2 7N H 2 O + 8S1 8NH 3 S2 + 6NO 2 7N H 2 O + 8S2 2NH 3 S1 + 2NO 2 N 2 + NH 4 NO 3 S1 + H 2 O + S1 NH 4 NO 3 S1 N 2 O + 2H 2 O + S1 2NH 3 S2 + 2NO 2 N 2 + NH 4 NO 3 S2 + H 2 O + S2 NH 4 NO 3 S2 N 2 O + 2H 2 O + S2 NO 2 SCR Model Results at SV:60k/h Over-prediction in NO x conversion at 150 C In general, reactions proceed on both sites, with different activation energies N 2 O slip model captures overall trend, but needs improvement 10/5/

32 NO 2 SCR Model N 2 O Hysteresis Result at SV: 60k/h Method 1 2NH 3 S1 + 2NO 2 N 2 + N 2 O + 3H 2 O + 2S1 2NH 3 S2 + 2NO 2 N 2 + N 2 O + 3H 2 O + 2S2 Method 2 2NH 3 S1 + 2NO 2 N 2 + NH 4 NO 3 S1 + H 2 O + S1 NH 4 NO 3 S1 N 2 O + 2H 2 O + S1 2NH 3 S2 + 2NO 2 N 2 + NH 4 NO 3 S2 + H 2 O + S2 NH 4 NO 3 S2 N 2 O + 2H 2 O + S2 N 2 O slip model captures overall trend, but needs improvement 10/5/

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 N 2 O and N 2 yields give information related to nitrate formation, stability, and impact on SCR efficiencies For standard SCR, identical N 2 O curves obtained during ramp up and ramp down indicating: Low N 2 O stabilization time during ramp down No hysteresis for standard SCR 10/5/