LOW TEMPERATURE LIMITERS TO CATALYST LIGHT-OFF

Transcription

1 LOW TEMPERATURE LIMITERS TO CATALYST LIGHT-OFF Gordon J.J. Bartley, Ph.D. - Southwest Research Institute CLEERS 18 April 27, 2015

2 Presentation Outline Background Project Objectives Catalyst Evaluated Individual Test Conditions and Results Conclusions This Presentation is Only a Summary Refer to SAE Paper for More Details, and SwRI for Further Details Paper #

3 Background More fuel efficient vehicles are resulting in lower exhaust temperatures. Based on exhaust temperature expectations for future engine technology, industry representatives predict light-off temperatures of ~150 o C will be required to meet emission regulations for new engines used to meet vehicle fuel economy standards. Lowering of the temperature at which catalysts become active to ~150 o C is extremely difficult and forms The 150 o C Challenge USDRIVE WORKSHOP, November 29-30, 2012 Future Automotive Aftertreatment Solutions: The 150 o C Challenge Workshop Report Paper #

4 Project Objectives 1. Identify low temperature limiters for a variety of relevant catalyst aftertreatment types 2. Postulate the mechanisms behind low temperature activity limitation 3. Consider ways in which to mitigate these limitations, facilitating low temperature activity The objectives are listed in relative priority for the project, but all are recognized as important to the overall goal. Paper #

5 Seven Catalysts Investigated A Wide, Shallow Dive Any one of these can be a lifetime s work TWC gasoline, stoichiometric DOC diesel, lean NGOx natural gas oxidation, lean LNT gasoline, lean NO X Fe-SCR diesel, lean NO X Cu-SCR diesel, lean NO X V-SCR diesel, lean NO X AMOx diesel, lean NH 3 Paper #

6 Low Temperature Catalyst or Low Temperature Catalysis? Considerable Efforts are Being Made to Develop Low Temperature Catalyst Formulations SwRI s Low Temperature Catalyst 100 % conversion > 150 o C 20% conversion at 100 o C Problem Solved! Paper #

7 We Cheated!! The Catalyst was a Standard Three-Way Formulation The Gas Mixture was : 10 % O ppm CO No H 2 O No NO x 2000 ppm H 2 No SO 2 Balance N 2 No hydrocarbons The Point? Today s catalysts are already capable of low temperature catalysis, but the environment is critical to effective low temperature catalysis Consider Both the Catalyst and the Conditions as a System and Look for System Solutions Paper #

8 Evaluation Procedure SwRI s USGR Gas Reactor Used Reverse Light-Off Forward Light-Off RLO FLO Paper #

9 Three-Way Catalyst 100,000 Mile Field Catalyst, Acid-Washed to Remove Deposits (phosphorus, zinc, calcium) Stoichiometric, Perturbated RLO FLO Pt = 24 g/ft 3 Pd = 39 g/ft 3 Rh = 6.5 g/ft 3 Concentration Gas Lean Rich Nitric Oxide (NO) 500 ppm 500 ppm Propene/Propane 2:1 (C 3 H 6 /C 3 H 8 ) 483 ppmc3 483 ppmc3 Carbon Monoxide (CO) ppm Hydrogen (H 2 ) ppm Oxygen (O 2 ) 0.65 percent 0 Carbon Dioxide (CO 2 ) 13 percent 13 percent Water (H 2 O) 14 percent 14 percent Nitrogen (N 2 ) Balance Balance Paper #

10 TWC Full Gas Mix CO Light-Off Initiated at 160 o C, but Protracted Propene & NO Coincident Paper #

11 TWC minus NO Removal of NO Clearly Lowers CO and HC Light-Off Temperatures NO is a Light-Off Inhibiter Full Gas Mix Minus NO Yu Lei et al., ChemCatChem 2011, 3, Paper #

12 N 2 O Formation N 2 O Formation Coincides with NO Activation NO Inhibition Mechanism Seems Plausible Full Gas Mix Use of an NO adsorber could improve low temperature activity - NO X storage typically NO NO 2 conversion, then NO 2 storage as nitrates - No NO 2 formation cold, so need NO storage as nitrite N 2 O formation Paper #

13 TWC minus Propene (C 3 H 6 ) Removal of C 3 H 6 Lowers CO Light-Off Temperatures Removal of C 3 H 6 Increases NO Light-Off Temperatures Full Gas Mix C 3 H 6 is Both a CO Light-Off Inhibiter and a NO Light-Off Promoter Paper #

14 TWC minus CO/H 2 Removal of CO/H 2 Increased Propene and NO Light-Off Temperatures CO/H 2 is a Light-Off Promoter FGM -CO/H 2 -RLO only Paper #

15 TWC - Summary NO Inhibits CO and HC C 3 H 6 Inhibits CO, but Promotes NO CO/H 2 is a Light-Off Promoter Solutions may include: cold start NO adsorber run slightly rich to increase CO, H 2 and alkenes, and reduce NO (supplemental O 2 may be needed) Paper #

16 Diesel Oxidation Catalyst Degreened Catalyst from 2007 MY Class 8 Truck Lean RLO FLO Pt = wt% Pd = wt% Gas Nitric Oxide (NO) Ethene (C 2 H 4 ) Carbon Monoxide (CO) Hydrogen (H 2 ) Oxygen (O 2 ) Carbon Dioxide (CO 2 ) Water (H 2 O) Nitrogen (N 2 ) Concentration 600 ppm 75 ppmc2 300 ppm 100 ppm 10 percent 5.6 percent 6.0 percent Balance Paper #

17 DOC Full Gas Mix CO T 50 Light-Off at 140 o C C 2 H 4 T 50 Light-Off at 246 o C Forward Light-Off Temperatures of C 2 H 4 & NO are Lower Than Reverse Light-Off Temperatures Inverse Hysteresis* A Product of Reactions Inhibits Reverse Light-Off NO 2? * Martin Votsmeier CLEERS 2014 Paper #

18 NO 2 Effect on Forward Light-Off 50:50 NO:NO 2 Mixture NO 2 Inhibits CO & Promotes Low Temperature C 2 H 4, but Inhibits Higher Temperature C 2 H 4 FGM + NO 2 Paper #

19 DOC minus NO X Removal of NO X Clearly Lowers CO and HC Light-Off Temperatures NO X is a Light-Off Inhibiter FGM NO Inhibition Mechanism Like TWC...? - NO Paper #

20 DOC minus CO Removal of CO Raised C 2 H 4 and NO Light-Off Temperatures CO is a Promoter of Low Temperature HC Light-Off FGM - CO Paper #

21 DOC - Summary NO Inhibits CO and C 2 H 4 CO Promotes C 2 H 4 C 2 H 4 Promotes NO Lean NO X catalysis Also, H 2, CO 2 and H 2 O Promote NO Light-Off Competative adsorption? Solutions may include: cold start NO adsorber increase CO, H 2 & reduce NO in exhaust Paper #

22 Natural Gas Oxidation Catalyst Used a TWC from an ISX-12G, Preconditioned with 150 Engine Hours (no NGOx available) Gas Concentration Lean RLO FLO Pt = 1.3 g/ft 3 Pd = 57 g/ft 3 Rh = 1.1 g/ft 3 Nitric Oxide (NO) Methane (CH 4 ) Ethane (C 2 H 6 ) Carbon Monoxide (CO) Hydrogen (H 2 ) Oxygen (O 2 ) Carbon Dioxide (CO 2 ) Water (H 2 O) Nitrogen (N 2 ) 500 ppm 1500 ppm 150 ppm 1200 ppm 280 ppm 10 percent 7.5 percent 8.0 percent Balance Paper #

23 NGOx Full Gas Mix CH 4 Oxidation was Primary Goal CH 4 T 50 Light-Offs Around 500 o C Clearly Not an Ideal Catalyst, but Trends Should Still be Valid Paper #

24 NGOx minus H 2 O Removal of H 2 O Clearly Lowers CO and HC Light-Off Temperatures CH 4 light-off lowered by o C FGM H 2 O is a Strong Light-Off Inhibiter - H 2 O Paper #

25 NGOx minus NO NO Inhibits CO Forward Light-Off, FGM but NO Promotes HC Light-Off Lean NO X catalysis NO is a Promoter for CH 4 Oxidation - NO Paper #

26 NGOx H 2 Effect H 2 Promotes CO and HC Light- Off FGM Increasing H 2 10x Further Improves CH 4 Oxidation Light- Off FLO 533 o C 501 o C RLO 492 o C 469 o C - H 2 Paper #

27 NGOx - Summary H 2 O Strongly Inhibits CH 4 Oxidation NO and H 2 Promote CH 4 Oxidation Solutions for Lower Temperature CH 4 Oxidation may Include: hydrophobic catalyst support increase NO, H 2 & reduce H 2 O in exhaust Paper #

28 Lean NO X Trap Fresh OEM LNT for 2011 VW Jetta 2.0L TDI RLO FLO lean/rich cycling 200s/50s Intentionally extended to create NO and NH 3 breakthroughs Pt = 78 g/ft 3 Pd = 13 g/ft 3 Rh = 7.7 g/ft 3 Concentration Gas Lean Rich AFR/λ 15.88/ /0.990 Nitric Oxide (NO) 30 ppm 30 ppm Propene/Propane 2:1 (C 3 H 6 /C 3 H 8 ) 67 ppmc3 67 ppmc3 Carbon Monoxide (CO) ppm Hydrogen (H 2 ) ppm Oxygen (O 2 ) 1 percent 0 Carbon Dioxide (CO 2 ) 7.4 percent 7.4 percent Water (H 2 O) 8 percent 8 percent Nitrogen (N 2 ) Balance Balance Paper #

29 LNT Cycle Averaging Complex 1 Hertz Data Simplified to Cycle Average Conversion Efficiency Paper #

30 LNT Differential Light-Off Behavior H 2 O Inhibits NO Light-Off CO Inhibits NO Light-Off HCs Inhibit NO Light-Off But C 3 H 6 Promotes NO Light- Off Solutions may include: cold start HC absorber decrease cold start CO Paper #

31 Fe-Zeolite SCR Catalyst Field-Aged, Moderate Mileage, Excellent Condition RLO only Forward light-off problems with NH 3 storage and NH 4 NO 3 formation Fast Reaction Mixture NO + NO 2 + 2NH 3 2N 2 + 3H 2 O Gas Nitric Oxide (NO) Nitrogen Dioxide (NO 2 ) Ethylene (C 2 H 4 ) Carbon Monoxide (CO) Hydrogen (H 2 ) Oxygen (O 2 ) Ammonia (NH 3 ) Water (H 2 O) Nitrogen (N 2 ) Concentration Lean 300 ppm 300 ppm 75 ppmc2 300 ppm 100 ppm 10 percent 600 ppm 6 percent Balance Paper #

32 Fe-Zeolite Full Gas Mix Good NO X Light-Off Just Above Urea Injection Minimum Temperature C 2 H 4 & CO Light-Offs Coincide with Downturn in NO X Efficiency concurrent oxidation of NH 3 Paper #

33 Fe-Zeolite NO X Reactions Removal of NO 2 (all NO) Switches to Standard Reaction with Higher Light-Offs 4NO + 4NH 3 + O 2 4N 2 + 6H 2 O Removal of NO (all NO 2 ) Results in Low Temperature NH 4 NO 3 Formation 2NO 2 + 2NH 3 N 2 + NH 4 NO 3 + H 2 O FGM - NO 2 - NO Paper #

34 Fe-Zeolite minus H 2 O Removal of H 2 O Lowered NO X, HC and CO Light-Offs H 2 O is an Inhibiter FGM - H 2 O Paper #

35 Fe-Zeolite - Summary Normal NO X Reaction Behaviors H 2 O Inhibits NO X Light-Off Solutions for lower temperature NO X light-off may include: Use of a different reductant than urea e.g. H 2 Paper #

36 Cu-Zeolite SCR Catalyst USGR-aged, 16 hrs, 775 o C, 14% O 2, 5% CO 2, 6% H 2 O, bal N 2 RLO only Same Gas Mix as for Fe-zeolite Gas Nitric Oxide (NO) Nitrogen Dioxide (NO 2 ) Ethylene (C 2 H 4 ) Carbon Monoxide (CO) Hydrogen (H 2 ) Oxygen (O 2 ) Ammonia (NH 3 ) Water (H 2 O) Nitrogen (N 2 ) Concentration Lean 300 ppm 300 ppm 75 ppmc2 300 ppm 100 ppm 10 percent 600 ppm 6 percent Balance Paper #

37 Cu-Zeolite Full Gas Mix Good NO X Light-Off Just Above Urea Injection Minimum Temperature C 2 H 4 & CO Light-Offs Coincide with Downturn in NO X Efficiency concurrent oxidation of NH 3 Paper #

38 Cu-Zeolite - Summary No Inhibiters Identified H 2 O, NO 2 & CO all Mild Promoters Solutions for lower temperature NO X light-off may include: Use of a different reductant than urea e.g. H 2 Paper #

39 V-SCR Catalyst Engine-Preconditioned, 24 hrs DAAAC Cycle Using 2004 Caterpillar C15 RLO only Same Gas Mix as for Fe-Zeolite Gas Nitric Oxide (NO) Nitrogen Dioxide (NO 2 ) Ethylene (C 2 H 4 ) Carbon Monoxide (CO) Hydrogen (H 2 ) Oxygen (O 2 ) Ammonia (NH 3 ) Water (H 2 O) Nitrogen (N 2 ) Concentration Lean 300 ppm 300 ppm 75 ppmc2 300 ppm 100 ppm 10 percent 600 ppm 6 percent Balance Paper #

40 V-SCR Full Gas Mix Excellent NO X Light-Off Below Urea Injection Minimum Temperature C 2 H 4 & CO Light-Offs Coincide with Downturn in NO X Efficiency concurrent oxidation of NH 3 Paper #

41 V-SCR minus H 2 O Removal of H 2 O Lowered NO X, HC and CO Light-Offs H 2 O is an Inhibiter NO X T 50 Light-Off at 145 o C! well below urea minimum temperature FGM - H 2 O Paper #

42 V-SCR - Summary H 2 O Inhibits NO X Light-Off No Other Inhibiters Outside of Normal SCR Behavior Solutions for lower temperature NO X light-off may include: Use of a different reductant than urea e.g. H 2 Paper #

43 AMOx Catalyst State-Of-The-Art Formulation (zeolite over Pt), Hydrothermally Aged 72 hrs at 620 o C Concentration RLO-FLO Pt = wt% Cu = wt% Gas Nitric Oxide (NO) Ammonia (NH 3 ) Ethylene (C 2 H 4 ) Carbon Monoxide (CO) Hydrogen (H 2 ) Oxygen (O 2 ) Carbon Dioxide (CO 2 ) Water (H 2 O) Nitrogen (N 2 ) Lean 15 ppm 100 ppm 75 ppmc2 300 ppm 100 ppm 10 percent 5.6 percent 6 percent Balance Paper #

44 AMOx Full Gas Mix RLO NH 3 T 50 at 232 o C FLO NH 3 Desorption (Negative Conversion Efficiency) and Elevated Light-Off at T 50 = 281 o C Paper #

45 AMOx minus ethene (C 2 H 4 ) Removal of C 2 H 4 Lowered NH 3 Light-Off by o C FGM C 2 H 4 is an Inhibiter If AMOx is Downstream of DOC/DPF/SCR, HCs May be Very Low Already If AMOx is Downstream of SCR Only, HCs Could Cause Issues - C 2 H 4 Paper #

46 AMOx minus H 2 O Reverse Light-Off Temperature Slightly Lower Forward Light-Off Temperature Unaffected FGM H 2 O is a Mild Inhibiter but Significantly More NH 3 Desorption at Cold Start Stored H 2 O reduces stored NH 3 If AMOx is Downstream of SCR Only, HCs Could Cause Issues - H 2 O If AMOx is Downstream of DOC/DPF/SCR, HCs May be Very Low Already Paper #

47 AMOx - Summary H 2 O, C 2 H 4 & CO are Inhibiters to NH 3 Light-Off O 2 is a Promoter for NH 3 Light-Off Solutions for lower temperature NH 3 light-off may include: Upstream DOC/DPF HC absorber to remove unsaturated HCs Paper #

48 Conclusions The Inhibiters and Promoters are Summarized in the Table THANK YOU Paper #