Development of a Durable Low- Temperature Urea-SCR Catalyst for CIDI Engines

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1 Development of a Durable Low- Temperature Urea-SCR Catalyst for CIDI Engines by Donovan Peña, Eric Coker, Ronald Sandoval, and James Miller Sandia National Laboratories Ceramic Processing & Inorganic Materials Diesel Engine Emission Reduction Conference Coronado, CA Aug. 29 Sep Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy s National Nuclear Security Administration under contract DE-AC04-94AL85000.

2 Take advantage of faster kinetics to increase conversion and expand temperature window Diesel Emissions Control Urea H 2 NCONH 2 Potential light duty configuration to meet Bin 5 emissions standards Oxidation Catalyst NO and HC SCR Catalyst Particulate filter NH 3 Slip Catalyst 4 NH NO + O 2 4 N H 2 O (medium) 4 NH NO + 2 NO 2 4 N H 2 O (fast)

3 Catalyst Development Issues High Selectivity NH 3 + NO x + O 2 N 2 X+ H 2 O N 2 O + H 2 O Urea Decomposition to NH 3 NH 2 -CO-NH 2(l) NH 3 + HNCO HNCO + H 2 O NH 3(g) + CO 2 Minimize Competing Reactions Low T: 2NH 3 + 2NO 2 NH 4 NO 3 + N 2 + H 2 O High T: 4NH 3 + 5O 2 4NO + 6H 2 O 4NH 3 + 4NO + 3O 2 4N 2 O + 6H 2 O

4 Typical Experimental Conditions Temperature ( C) NO (ppm) NO 2 (ppm) NH 3 (ppm) 350 O 2 (%) 14 CO 2 (%) 5 H 2 O (%) 4.6 GHSV (h -1 ) 30, ,000 NO 2 simulates cold-start conditions NH 3 :NO x in the feed is 1:1 Powder catalysts diluted 1:1 with cordierite C decreasing, 30 minute isothermal holds NO x conversion (%) defined as: 1 N 2 O selectivity (%) defined as: N 2 O / (N 2 O + N 2 ) ( NO + NO ) ( out) 2( out) 100 * NO + NO ( in) 2( in)

5 LEP Staged Testing Protocol Catalyst performance evaluated: 1. Fresh, using stated typical experimental conditions 2. Fresh, as a function of NO:NO 2 ratio NO to NO 2 3. After hydrothermal aging 16 hours at typical experimental conditions at 600 C*, 700 C, and 800 C 4. After sulfur aging 20 ppm SO 2 at 350 C* or 670 C at typical experimental conditions (minus NH 3 ) for 24* and 48 hours * Items in bold represent minimum performance requirement

6 Experimental Apparatus NH 3 /N 2 MFCs Thermocouple s NO 2 /N 2 NO/N 2 HC Powder GHSV = 30, ,000 h - 1 FTIR GC CO 2 N 2 Air Monolith GHSV = 30,000 h -1 H 2 O Heating Tape

7 Hydrous Metal Oxide Synthesis Hydroxide Addition Ti-alkoxide + Si-alkoxide + NaOH Hydrolysis soluble intermediate Acetone Water Methanol soluble intermediate NaTi 2 O 5 H Acidification and Ion Exchange M n+ + n NaTi 2 O 5 H M(Ti 2 O 5 H) n + n Na + Impregnation incipient wetness (powder) Activation/Pretreatment (600 C in air for 4 h) Catalyst Monolith Catalyst + Al 2 O 3 + H 2 O + grinding slurry slurry + monolith 425 C in air for 4 h final monolith

8 Effect of Synthesis Conditions on S.S.A. BET S.S.A. (m 2 /g) BET S.S.A. of HTO:Si Metal Oxide Catalysts as of Function of Total Metal Concentration D6 D3 9 vol.% H 2 O D Metal Concentration (mol/l) NO Conversion / N2O Selectivity C m = 0.7 mol/l C m = 0.3 mol/l C m = 5 mol/l Catalyst 1139/3-13BcD3 Catalyst 1139/3-68AD6 Catalyst 1139/3-68BD Temperature (C) Less concentrated hydrolysis solution increases resulting surface area by 3 May be attributed to slower rate of hydrolysis from decreased metal concentration Similar results seen with supports only No linear relationship between catalytic activity and surface area All samples were calcined at 600 C in air and degassed at 400 C for 14 h Powders 1:1 NO 2 140,000 h -1

9 Comparison of Monolith and Powder Data Powder 1:1 NO x Conversion powder 28 wt.-% 12 wt.-% 5 NO 2 140,000 h -1 Monolith s 5 NO 2 30,000 h Temperature ( C) Powders tested at high SV to simulate the contact time of 25 wt.-% catalyst on monolith High-loaded monoliths (>16 wt.-%) approach powder performance

10 Optimization of Catalyst Composition Powders 1:1 Catalyst D2 NO x Conversion NO 2 140,000 h / 1139/1-54C 2%CuO, 1%MnO Catalyst D / 1139/3-13B 2%CuO, 2%MnO Catalyst D4 Temperature ( C) Change concentration of same two components Have the ability to tune catalytic performance tradeoffs in low and high temperature activity 1169 / 1139/3-13C 2%CuO, 4%MnO

11 Hydrothermal Treatment V 2 O 5 -WO 3 Monolith Sample Catalyst D2 Powder Sample NO x Conversion SV 30,000h -1 5 NO 2 NO x Conversion SV 30,000h -1 5 NO 2 Fresh Activity Fresh Activity Aged 16 h at 600 C Aged 16 h at 600 C Temperature, C Temperature, C Minor loss in activity after short term hydrothermal treatment More relative activity retained with D2 Hydrothermal treatment at feed concentration (4.6% H 2 O)

12 SO2 Tolerance V 2 O 5 -WO 3 Monolith Sample Catalyst D2 Powder Sample NOx Conversion SV 30,000h NO 2 NO x Conversion SV 30,000h -1 5 NO 2 Fresh Fresh After 65 hrs. w/ 20 ppm SO 2 Aged 24h, 20 ppm SO Temperature, C SO 2 Aging At 350 C without NH Temperature, C Some loss in low temperature activity

13 Hydrocarbon Testing NO x Conversion V 2 O 5 -WO 3 Monolith Sample SV 30,000h -1 NO ppm propylene 130 ppm n-octane Temperature, C No hydrocarbon With hydrocarbon After hydrocarbon testing Not a direct comparison Trends are important NO x Conversion Catalyst D2 Monolith Sample SV 30,000h -1 NO 2 34 ppm propylene 38 ppm n-octane Temperature ( C) C 3 & n-c 8 suppress conversion ca. 1 above 300 C, (HC oxidation) No change on addition of 60 ppm toluene (>12 h TOS) Activity recovered when HCs removed

14 Summary Optimizing synthesis parameters leads to enhanced catalyst surface areas Nonlinear relationship between activity and surface area Catalyst development performed under a staged protocol Catalytic materials with desired properties have been identified Meet stage requirements Performance can be tuned by altering component concentrations Optimization still necessary at low temperatures Better activity and tolerance to SO2 V2O5-based materials ruled out because of durability issues Future work will focus on improving overall low temperature activity

15 Acknowledgments The authors wish to thank the Low Emission Technologies Research and Development Partnership (Ford, General Motors, and DaimlerChrysler) and the U.S. Department of Energy for funding this work