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Strategies for Improving Sulfur Tolerance in Diesel LNT Systems

Strategies for Improving Sulfur Tolerance in Diesel LNT Systems. Friedemann Rohr Umicore AG & Co. KG Rodenbacher Chaussee 4 D-63403 Hanau-Wolfgang. Automotive catalysis in the context of the energy debate. Automotive catalysis in the context of the energy debate.

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Strategies for Improving Sulfur Tolerance in Diesel LNT Systems

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  1. Strategies for Improving Sulfur Tolerance in Diesel LNT Systems Friedemann Rohr Umicore AG & Co. KG Rodenbacher Chaussee 4 D-63403 Hanau-Wolfgang

  2. Automotive catalysis in the context ofthe energy debate

  3. Automotive catalysis in the context ofthe energy debate • Fuel economy fast becoming the most important development criteria in the industry. • Appeal of the diesel still strong in Europe, partly due to good fuel economy. • Business case for the diesel in light duty applications still unclear in North America.

  4. Improving sulphur resistance – key to enhancing LNT-performance • Development efforts in Europe for EU6 are picking up steam. • LNT-cDPF emerges as preferred system for light duty diesel applications. • The viability of the concept hinges on the ability to deSOx the LNT under moderate conditions.

  5. Agenda: • Aging phenomena in LNTs • Basics of sulfur chemistry in LNTs • Desulfation and the temperature challenge • Advances in sulfur resistance

  6. Working principle of an LNT H2, CO, CO2 NO, O2 SO2 NO2 SO3 CO2, N2 NOx+O2 CO2 CO   Ba(NO3)2 BaCO3 Ba(NO3)2 BaSO4 BaCO3 Pt Pt, Rh BaSO4 storage phase l > 1 regeneration l < 1

  7. Deactivation through thermal aging BaCO3 Pt Al2O3/CeO2

  8. Deactivation through thermal aging loss of Pt-dispersion BaCO3 Pt Al2O3/CeO2

  9. Deactivation through thermal aging loss of storage capacity through composite formation BaCO3 Pt composite composite Al2O3/CeO2

  10. Deactivation through sulfur poisoning loss of storage capacity through sulfate formation BaSO4 BaCO3 Pt Al2O3/CeO2

  11. Basics of sulfur chemistry (F.Rohr et.al., Appl. Catal. B 56 (2005) 201) Two-brick configuration Sulfation on the engine bench: Cores are taken from both bricks: 5’’ (DeSOx on synthetic gas bench (SGB)) Desulfation and/or analysis on entire core or segments: 2“ (activity test on SGB, IR, TPR, TPD, SEM) 1“ (S-post mortem)

  12. Post-mortem sulphur analysiserror margin: 0,01%

  13. Transmission IR

  14. IR: change relative to fresh sample

  15. SEM-EDXafter sulfation, inlet side, first brick

  16. SEM-EDXafter desulfation, inlet side, first brick Ba and Ce-sites are not correlated Ba and S-sites are correlated

  17. Sulfur Poisoning on a fresh LNT

  18. Sulfur poisoning Sulfur poisoning vs. thermal aging NOx conversion [%] Temperature [°C]

  19. Thermal aging Sulfur poisoning vs. thermal aging NOx conversion [%] Temperature [°C]

  20. Simulating LNT aging onthe engine bench desulfation DPF-burn out sulfation

  21. The temperature challenge Daimler E-320 Bluetec I T-measurement CDPF NSC DOC FTP-75 NEDC

  22. experimental data for NO/O2 feed over oxidation catalyst NO-oxidation, a key step in lean exhaust aftertreatment calculated for 6% O2 at atmospheric pressure controlled by kinetics controlled by thermodynamics

  23. DeSOx strategies • LNT close to the engine, hot DeSOx, low H2S, durable LNT (Daimler Bluetec). • Underfloor, cold DeSOx, higher H2S yield, H2S control device maybe necessary. • Increase rich pulse duration and richness generally improves S-release, H2S formation and HC/CO control might be an issue.

  24. Diesel LNT development direction Catalyst A Catalyst B Catalyst C Not to exceed:  800°C  750°C  720°C Required for DeSOx: Temperature  750°C  650°C  600°C

  25. Improving sulfur release propertiesSulfur TPD testing Rate of sulfur release: C > B > A

  26. Durability testing on the engine benchNOx-conversion over the hot NEDC cycle Operating A at lower T(DeSOx) improves durability

  27. The “hot” caseDaimler E 320 Bluetec I for Tier2 Bin8 catalysts supplied by Umicore Thermistor DOC 0.6 L Thermistor LNT 3.1 L SCR cDPF Delta P 2.6 L 3.6 L Source: http://www.greencarcongress.com/2006/01/mercedes_to_int.html

  28. The “cold” caseVW Jetta for Tier2 Bin5 catalysts supplied by Umicore

  29. Limiting the impact of sulfur • Improving formulation properties. • Finding the right compromise (LNT placement, durability vs. DeSOx requirements). • Exotic concepts (sulfur traps, valve systems, H-assisted DeSOx, in pipe fuel injection).

  30. Improving the formulation‘s sulfur resistance Main approaches: • Controlling/finetuning basicity. • Fast screening.

  31. +H2O +H2O H2SO4 HNO3 The main dilemma SO3 NO2

  32. +BaO +BaO BaSO4 Ba(NO3)2 The main dilemma SO3 NO2

  33. Improving the formulation‘s sulfur resistance • SO2/SO3 and NOx have similar chemical properties. • Selective chemistry elusive in high temperature solid state chemistry. • Homogeneous ternary/quaternary oxids allow for finetuning and tayloring of various properties.

  34. Finetuning properties of complex oxides pure AO AxByO pure BO

  35. G. Ertl, H.J. Freund: “Catalysis and Surface Science”, Phys. Today, 32, (1999). Gerhard Ertl, 2007 Nobel Prize in Chemistry for achievements in heterogeneous catalysis „Modern surface physics is transforming the black art of catalysis, revealing a fascinating choreography followed by reacting atoms and molecules“

  36. Fundamental understanding of heterogeneous catalysis still sketchy catalysis complexity gap surface science pressure gap

  37. Typical workflow in catalyst development catalyst preparation • previous results • findings from a study on model systems • educated guess • hunch good enough? (y/n) catalyst testing Upscaling marketing selling

  38. High throughput evaluationCatalyst cores on the engine bench • Cores are aligned in a symmetrical fashion • The entire exhaust flows through the cores • Exhaust enters the reactor through a symmetrical inlet cone

  39. High throughput catalyst development Reactors Characterisation Sample Library

  40. Reactor module: parallel opening and closing of reactor units Top View Bottom View

  41. “Exotic concepts”: valve for off-line DeSOx 3-way valve LNT 1 LNT 2 DeSOx LNT 2 „offline“

  42. “Exotic concepts”: DeSOx assisted by external fuel processing device Injection of H2/CO from a fuel processor unit LNT 1

  43. “Exotic concepts”: Sulfur trap Source: Kohei Yoshida et.al., Toyota Motor Corporation, SAE 2007

  44. Conclusions • New LNT formulations with improved sulfur release are being developed. They are key for future LDD applications in both Europe and North America. • Material design and fast screening methodology are key tools in improving sulfur resistance. • Exotic concepts to address sulfur poisoning are being explored, economic viability however is still unclear.

  45. Thank you for your attention!

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