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Investigation of Aging Mechanisms in Lean NOx Traps

Investigation of Aging Mechanisms in Lean NOx Traps. PI: Mark Crocker Center for Applied Energy Research, University of Kentucky February 26, 2008. “This presentation does not contain any proprietary or confidential information” . Purpose of Work.

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Investigation of Aging Mechanisms in Lean NOx Traps

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  1. Investigation of Aging Mechanisms in Lean NOx Traps PI: Mark Crocker Center for Applied Energy Research,University of Kentucky February 26, 2008 “This presentation does not contain any proprietary or confidential information”

  2. Purpose of Work • Understand main chemical and physical processes occurring during LNT aging • Correlate washcoat composition with catalyst durability Effect of Pt, Rh, Ba, CeO2, CeO2-ZrO2 • Establish effect of LNT catalyst aging on NOx performance and desulfation behavior • Provide insights that will assist the design of more durable catalysts and/or allow for optimized catalyst operation as it ages

  3. Barriers • Aftertreatment needed to meet NOx emission goals • Engine conditions that have the highest overall efficiency typically contain NOx levels exceeding the 2010 regulations • Limited durability of LNT catalysts impediment to widespread use • Deeper understanding of “commercial” catalyst materials required:- role of individual components- effect on aging characteristics • Providing insights that optimize catalyst operation over the lifetime of the vehicle • Improves catalyst efficiency and therefore minimizes fuel penalty • Aftertreatment needed to meet NOx emission goals • Engine conditions that have the highest overall efficiency typically contain NOx levels exceeding the 2010 regulations • Limited durability of LNT catalysts impediment to widespread use • Deeper understanding of “commercial” catalyst materials required:- role of individual components- effect on aging characteristics • Providing insights that optimize catalyst operation over the lifetime of the vehicle • Improves catalyst efficiency and therefore minimizes fuel penalty I added some points that specifically relate to DOE’s mission of reducing our dependance on Foreign oil, i.e. improve efficiency I added some points that specifically relate to DOE’s mission of reducing our dependance on Foreign oil, i.e. improve efficiency

  4. Approach • Employ well characterized model catalysts which are representative of 2nd generation LNT formulations use of ceria; also of relevance for lean-burn gasoline LNTs • Examine effect of washcoat components/loadings on catalyst durability:  systematic variation of component concentrations: Pt, Rh, Ba, CeO2(-ZrO2) • Employ realistic aging protocol, with simultaneous measurement of catalyst NOx storage/reduction performance • Perform detailed physico-chemical characterization of aged catalysts • U. of Kentucky, ORNL, Ford and Umicore as partners

  5. Performance Measures • Synthesize model LNTs with sequential variation of component loadings: Pt, Rh, Ba, CeO2(-ZrO2) • Evaluate catalysts to determine key component effects:- NOx performance (conversion, selectivity)- intra-catalyst chemistry- desulfation behavior • Age catalysts in realistic and reproducible manner for subsequent studies (bench reactor + physico-chemical analysis)

  6. Accomplishments • Preparation of model monolith and powder catalysts completed • In situ DRIFTS and microreactor experiments to examine role of CeO2 in NOx storage and reduction • Evaluation of NOx reduction performance on ORNL bench reactor (with focus on effect of CeO2 loading) • Use of SpaciMS to study effect of CeO2 loading on intra-catalyst chemistry (H2 generation and consumption) • Desulfation studies at Ford Motor Co. (effect of component loadings on desulfation efficiency) • Ford LNT aging cycle implemented on UK bench reactor – catalyst aging on-going See notes section

  7. Wide Range of Monolithic Catalyst Compositions • Target washcoat loading = 260 g/L • Actual average loading = 262 g/L, stand. dev. = 16.6 g/L (6.3%) • Monoliths coated by…

  8. 0 g CeO2/L 50 g CeO2/L 100 g CeO2/L 100 100 g CeO2-ZrO2/L 90 80 100 70 90 60 (%) 80 50 NOx conversion (%) 2 70 40 60 30 Selectivity to N2 (%) 50 20 40 10 30 0 20 150 °C 250°C 350 °C 450 °C 10 0 Temperature (°C) 150 °C 250°C 350 °C 450 °C Temperature (°C) Ceria Addition Improves N2 Selectivity and Low Temperature Performance • Ceria improves performance for T< 350°C • Most significant at 150°C • Ceria-addition improves N2 selectivity • increases w/ OSC: 30-0<30-50<30-100<30-100Z Selectivity to N2 NOx conversion Be aware that there is animation on this slide

  9. Ceria Improves Effective NOx Storage Capacity at 150 °C • NOx storage capacity improves with increasing ceria loading • NO2 in effluent shows NO to NO2 oxidation not limiting for 30-0 and30-50 • Rich phase NOx release also increases with ceria loading • More NOx released with ceria-based LNTs  reduction kinetics are too slow It may be helpfully to include something that reminds the audience what 30-0 means…maybe (Ba-Ce) somewhere

  10. NH3 Decreases with Increasing Ceria T = 350 oC • Significant NH3 formation: 30-0 > 30-50 > 30-100 > 30-100Z

  11. Studies with Model Powder Catalysts Provide Basis for Explaining Monolithic Catalyst Results • In situ DRIFTS studies performed on two model powder catalysts: • PBA: 1 wt% Pt/BaO/Al2O3 (equivalent to monolith catalyst 30-0) • PBAC: PBA (74 wt%) + 1 wt% Pt/CeO2 (26 wt%), physical mixture (equivalent to monolith catalyst 30-50) Bullet spacing was weird, so I modified it In situ DRIFTS spectra during lean-rich cycling: • In situ DRIFTS: • only a fraction of stored NOx is purged during L/R cycling • PBAC shows superior rich phase regeneration • Microreactor results consistent • PBAC shows superior dynamic NOx storage capacity while cycling between lean and rich Lean Rich Conditions: lean phase (6 min): 300 ppm NO and 8% O2; rich phase (0.5 min): 5625 ppm CO, 3375 ppm H2, with 5% H2O and 5% CO2 added in both phases.

  12. Intra-catalyst Chemistry: H2 Concentration Profile from SpaciMS (T = 350 °C) During testing w/ NOx During OSC Is it possible to have all of these on the same scale? • Rich phase of testing of monolithic catalysts w/ NOx: Significantly more H2 produced over 30-100 than 30-0. However, H2 was largely consumed at the end of the bed for 30-100 Should probably mention WGS since the H2 concentration increases w/NOx

  13. SpaciMS: Comparison of 30-0, 30-100 and 30-100Z during L/R cycling(T = 350 °C) 30-100 30-0 30-100Z Outlet CO concentrationduring rich purge Change title name to the conclusion of the slide…which is? WGS occurs? CeZr is a hog?

  14. Effect of Ceria on Intra-Catalyst H2Concentration during Rich Purging • Significant intra-catalyst H2 generation observed for CeO2-containing catalysts (via WGS reaction) • Same catalysts show low outlet H2 concentrations (due to reaction with stored oxygen - towards rear of catalyst, rate H2 cons. > rate H2 prodn., due to CO having been largely consumed (supported by IR) • For 30-100Z, OSC is so high that H2 is rapidly depleted in front portion of catalyst balanced OSC required!

  15. Desulfation Studies: Effect of Catalyst Composition on Efficiency of Sulfur Removal Conditions:Sulfation: 350 °C, 100 ppm SO2,10% O2, 5% CO2, 5% H2O, bal. N2; ca. 2 g S/L cat.;Desulfation: 1% H2, 10 min, bal. N2 Key:Pt-100 = same as 30-50 but with half the Rh loading (10 vs. 20 g Rh/cuft)Pt-50 = same as Pt-100 but with half the Pt loading (50 vs. 100 g Pt/cuft) • Beneficial effect of ceria confirmed • Reduction of precious metal content has adverse effect

  16. Catalyst Aging • Goal is to subject model monolith catalysts to realistic accelerated aging for subsequent reactor studies and physico-chemical characterization • Catalyst aging on automated bench reactor • Initial aging to 50 cycles(ca. 50-75 k miles road equivalent based on fuel sulfur content) • Catalyst performance check every ~10 cycles

  17. LNT Aging Protocol Aging profile for catalyst 30-100 • Based on Ford protocol • Optimized desulfation temperature balances desulfation with thermal deactivation

  18. Technology Transfer • Technology transfer via Ford Motor Co. (project partner) • Model monolith catalysts prepared in this project currently being utilized in Ford R&D (Bob McCabe): - fundamental studies pertaining to catalyst sulfation and desulfation - effect of catalyst composition on selectivity to different N-species • Joint U. of Kentucky/Ford project planned as follow up to current DOE-sponsored project (Ford University Research Program) • Results of the project presented at conferences and in the literature • 3 publications, 7 presentations and counting…

  19. Publications, etc. Publications: • Y. Ji, J.-S. Choi, T. J. Toops, M. Crocker, M. Naseri, Influence of Ceria on the NOx Storage/Reduction Behavior of Lean NOx Trap Catalysts, Catal. Today, in press. • Y. Ji, T.J. Toops, M. Crocker, “Effect of Ceria on the Storage and Regeneration Behavior of a Model Lean NOx Trap Catalyst”, Catal. Lett. 119 (2007) 257. • Y. Ji, T.J. Toops, U.M. Graham, G. Jacobs and M. Crocker, “A kinetic and DRIFTS study of supported Pt catalysts for NO oxidation”, Catal. Lett. 110 (2006) 29. Presentations: • Y. Ji, T.J. Toops and M. Crocker, “Effect of Ceria Addition on the Regeneration of a Model LNT Catalyst”, Tri-State Catalysis Society Fall Symposium, Lexington, KY, November 19, 2007. • Y. Ji, T.J. Toops, J.-S. Choi, M. Crocker, “Composition-Activity Relationships in Lean NOx Trap Catalysts”, Europacat VIII, Turku, Finland, August 26-30, 2007, paper P14-9. • Y. Ji, T.J. Toops, J.-S. Choi, M. Crocker, “Investigation of Aging Mechanisms in Lean NOx Trap Catalysts”, 1st Annual DOE Semi-Mega Merit Review Meeting, Crystal City, VA, June 18-19, 2007. • Y. Ji, T.J. Toops, J.-S. Choi, M. Crocker, “Effect of CeO2 on the Storage and Regeneration Behavior of Lean NOx Traps”, 20th North American Catalysis Society Meeting, Houston, TX, June 17-22, 2007, paper O-S4-41. • Y. Ji, T.J. Toops, J.-S. Choi, M. Crocker, “The Effect of CeO2 on the Performance of Lean NOx Trap Catalysts”, 10th Cross-Cut Lean Exhaust Emissions Reduction Simulation (CLEERS) Workshop, Dearborn, MI, May 1-3, 2007. • Y. Ji, T.J. Toops and M. Crocker, “Effect of Ceria Addition on the Regeneration of a Model LNT Catalyst”, Southeastern Catalysis Society Fall Symposium, Asheville, NC, September 18, 2006. • Y. Ji, T.J. Toops, U.M. Graham, G. Jacobs and M. Crocker, “A kinetic and DRIFTS study of supported Pt catalysts for NO oxidation”, 9th Cross-Cut Lean Exhaust Emissions Reduction Simulation (CLEERS) Workshop, Dearborn, MI, May 3-4, 2006.

  20. Plans for Next Fiscal Year • Complete accelerated aging of monolith catalysts according to Ford cycle • Characterize NOx storage and reduction properties of aged model monolith catalysts: ORNL bench reactor, with use of spaci-MS • Performed detailed physical characterization of aged catalysts:SEM, TEM, N2 physisorption, H2 chemisorption, XRD • Derivation of LNT deactivation model: spatial resolution possible?

  21. Summary (1) • Model LNT catalysts have been prepared & characterized with systematic variation of Pt, Rh, Ba and CeO2(-ZrO2) loadings • Powder and core tests on the fresh catalysts have identified significant effects associated with the presence of ceria:- increased NOx storage, particularly at low temperatures - increased water-gas shift activity - improved selectivity to N2 during reduction of stored NOx (versus NH3)- significantly higher NOx conversion levels at T  250 C- sizeable exotherms during rich operation- lowering of desulfation temperatures

  22. Summary (2) • SpaciMS studies have revealed a strong dependency of intra-catalyst H2 concentration profiles on the ceria/oxygen storage content in model LNT catalysts  need for balanced OSC • Correlations have been identified between catalyst performance and Ba and Pt loadings • The Ford LNT aging cycle has been implemented at the U. of Kentucky

  23. NOx Abatement R&D(CRADA with ITEC) • Relevance • Understanding emission control chemistry over a wide range of engine conditions essential for model development and fuel efficiency • Approach • Evaluate engine-aged LNTs provided by ITEC • Perform detailed kinetic study to provide data for models and identify limiting factors • Technical Accomplishments • Demonstrated reductant activity is key limitation at low temperature • Identified NH3 and N2O trends with temperature and space velocity • Technology Transfer • Work closely with ITEC to define experiments and share results • Future Research • Transition efforts to SCR kinetics, characterization and aging effects We like to put a slide like this up while we are answering questions (don’t talk to it). It’s from another talk, so you will need to change the words, but these are the questions that the reviewer is answering, so it serves as a guideline, incase they missed something.

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