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Population and vehicles

Population and vehicles. People like the car: it gives the possibility to move fast and far It gives freedom. Motor vehicles. Urban population. World population. Air pollution. MOBILE SOURCES EXHAUST HYDROCARBONS (HC) CARBON MONOXIDE (CO) NITROGEN OXIDES (NO X ) SULFUR COMPOUNDS

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Population and vehicles

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  1. Population and vehicles People like the car: it gives the possibility to move fast and far It gives freedom Motor vehicles Urban population World population

  2. Air pollution MOBILE SOURCES EXHAUST HYDROCARBONS (HC) CARBON MONOXIDE (CO) NITROGEN OXIDES (NOX) SULFUR COMPOUNDS PM10

  3. Pollutant emission in the USA 1995 NOx 25 CO 80 VOC 30 Transportation share SO2 26 Millions of tons TransportationOther

  4. EU - Pollutant emission from transportation Million of tons 24 25 20 11 15 7.5 10 4.6 4.5 4.0 5 2.4 1.5 CO 1.5 0.9 0 0.8 NO 0.6 HC

  5. Sources of Volatile Organic Compounds (VOC) Automotive sources 38% Non automotive sources 62% 5% Manufacturing 7% Distribution 5% Refuelling 59% Exhaust 24% Evaporative

  6. European emission limits for CO 100% = Uncontrolled exhaust (60 g CO / Km) g / Km * Cold start

  7. Possible solutions Hydrogen car Fuel cell technology

  8. Hydrogen storage on - board Compressed Gas Storage Tanks Heavy and space / safety concern Metal hydrides Heavy

  9. Hydrogen storage on - board Possibility of H2 storage in SWCN (up to 67 wt %) A.C. Dillon et al. Nature386 (1997) 377. A.Chambers et al. J. Phys.Chem. B102 (1998) 4253. H2O / H2 storage in carbon nanofibers (< 2 wt%) R.T Yang et al. Carbon38 (2000) 623.

  10. Steam Reforming steam reforming HC + H2O  CO / CO2 / H2 CH4 + H2O  CO + 3H2 CH4 C-H 420 kJ/mol. CnH2n+2 C-H 350-400 kJ/mol C-C 320 kJ/mol Dry reforming CH4 + CO2 2CO + 2H2 water-gas shift CO + H2O  CO2 + H2 Methanation CO + 3H2 CH4 + H2O Unwanted reactions Boudouard reaction 2CO  C + CO2 methane cracking CH4 C + 2H2

  11. Steam Reforming burners CH4 : H2O = 1 : 3.7 P = 33 atm Outlet gas composition 44% H2O, 39% H2, 5% CO, 6% CO2, 6% CH4 Outlet Temperature 760°C DH = 214 kJ/mol 63% of the heat absorbed to the gas is used by the reaction, 37% is converted into a temperature increase. parallel reactor tubes The gas passes up through vertical reactor tubes, typically 10 meters long and 10 cm in diameter. Heat is supplied to the tubes by burners.

  12. Steam Reforming A typical catalyst consists of 15% NiO and 85% MgAl2O4. The catalyst is activated by reduction with H2. The active catalyst contains crystallites of metallic Ni with diameter 15-150 nm, the active area of Ni is 5-6 m2/g. Reaction mechanism CH4 + n*  CHx*n + (4-x)/2 H2 CHx*n + O*  CO + x/2 H2 + (n + 1)* H2O* + *  O* + H2 H2 + 2*  2H* * adsorption site Temperature gradients and gas film diffusion are serious complications for kinetic studies.

  13. Fuel Air H2O Reformer CO, H2 Reforming / Partial oxidation Methanoldecomposition HC + O2 CO + 2 H2 CH3OH CO + 2 H2 HC + H2O CO + 3 H2 On board H 2 production Ni, Pd, Pt over CeO2, ZrO2 and CexZr1-xO2 Fuel = CH4, HC, diesel, methanol,…

  14. Hydrogen production in Italy from methane? HC + O2 (N2) CO2 + H2O + NOX + CO + HC + soot … CH4 H2 fuel cells H2O 1998 58 billions m3 2010 90 billions m3 1/3 from Italy 2/3 from Russia, Algeria, Holland, Norway.

  15. Fuel processor development implies chemical system miniaturization technology Estimated reformer productivity: 600 mole H2 m-3 hr-1 Reformer volume for 50 kWe 5 m3

  16. steam + natural gas reactor wall Tfurnace Tfilm Treactor Tcatalyst Heat Flow reforming products Packed bed steam reformer: commercial technology

  17. Packed bed steam reformer volume • Twall:1000°C Tgas: 750°C • Pellet size 1/8” • Tube diameter 1.5” • Re = 740 • Volume: 16 liter

  18. Reforming feed CH4 / H2O Plate reformer with catalyst-packed passages Plate dimensions: 3 x 7 in Number of passages: 50 Volume required for heat transfer: 2 liter Catalyst volume: 7 liter

  19. Combustion catalyst Metal foil Combustion feed CH4 / air Reforming feed CH4 / H2O Reforming catalyst Plate reformer with catalyst-coated plates • Concept • steam reforming and fuel combustion occur on a catalyst-coated thin plate. The combustion reaction on one side of the plate provides heat to the endothermic steam reforming reaction on the other side

  20. Plate reformer with catalyst-coated plates • Plate dimensions: 3 x 7 in • Number of passages: 50 • Volume required for mass transfer: 1.2 liter

  21. H2O Fuel Air H2O Reformer WGSR Water-GasShiftReaction CO + H2OCO2 + H2 Cu, Ni, Fe, Co, Pd, Pt on CeO2 Au/ CeO2 On board H 2 production CO, CO2, H2

  22. Water-gas shift CO + H2O CO2 + H2 Thermodynamics likes low temperatures, but kinetics is too slow.

  23. H2O Fuel Air H2O Reformer WGSR PReferential OXidation Pt / Al2O3 : CeO2 Au / CeO2 CuO / CeO2 On board H 2 production O2 PrOx CO2, H2,H2O

  24. H2O Fuel Air H2O Reformer WGSR O2 PrOx H2,CO2, H2O Air On board H 2 production Fuel cell CO2, H2O

  25. Possible solutions Hydrogen car Fuel cell Electric car Technical problem - batteries

  26. Possible solutions Hydrogen car Fuel cell Electric car Technical problem - batteries Hybrid car Combustion engine Fuel tank Batteries Electricengine HondaInsight;ToyotaPrius

  27. Possible solutions Hydrogen car Fuel cell Electric car Technical problem - batteries Hybrid car Catalytic converters - TWC

  28. Possible solutions Hydrogen car Fuel cell Electric car Technical problem - batteries Hybrid car Catalytic converters – TWC Cycling - walking

  29. Properties of a suitable catalyst Highly active: Conversion > 98%. 50-100 liters of exhaust to be converted in 1 sec per liter of catalyst. Highly selective: H2O, CO2 and N2 as products. Thermally stable: working temperature 350-1100°C. Long life: 160.000 Km.

  30. Exhaust emissions vary as a function of air-to-fuel ratio (A/F) STOICHIOMETRIC COMBUSTION (A/F = 14.6 - 14.7) C8H18 + 12.5 O2 + 12.5 * 3.76 N2 9 H2O + 8 CO2 + 12.5 * 3.76 N2 Air to fuel ratio, by weight Engine powerNO X 5 HydrocarbonsCO

  31. TWC: How is the exhaust converted? 3 way catalyst • CO oxidation: • CO + ½ O2 CO2 • HC oxidation: • HC + O2 CO2 + H2O • NO reduction: • NO + ½ CO  ½ N2 + CO2 • HC + 2 NO  CO2 + N2 + H2O • Catalyst: Pt (Pd) / Rh / Al2O3 / Cex Zr1-xO2

  32. Gas phase diffusion Productdesorption NO Dissociativeadsorption CO Surfacediffusion CO2 Surfacereaction Molecularadsorption Adsorbedproduct Metal Support

  33. Three-way catalysts Ms, p NO e- Md Fermi Level 2 p* 1 s 1 p Rh Pd Pt Rh for NO reduction Pt and Pd for CO and HC oxidation nuclear charge 4 d 4d 5d R. Hoffmann et al., J.Phys. Chem., 97 (1993) 7691.

  34. Temperature dependence of conversions 100 50 0 CO HC Conversion / % NO 473 573 673 773 Temperature / K

  35. Cold start HC - adsorber Catalyst HC retained by adsorber • Warmed-up HC - adsorber Catalyst HC released from adsorber and converted by catalyst Options for the reduction of thecold start emissions Hydrocarbons adsorber

  36. Electrically heated catalyst (EHC) Quick heat-up of the converter EHC Main Catalyst Start-up converters (close-coupled converters) Possible through new thermostable washcoats Heat up quicker - handles low load exhaust Engine Main catalyst Start-up converter Options for the reduction of thecold start emissions

  37. Light-off catalyst Pt : Pd : Rh 5.3 g/l 1 : 28 : 1 3.7 g/l 1 : 14 : 1 2.8 g/l 1 : 16 :1 1.8 g/l 5 : 0 : 1

  38. Three-way catalyst CO NOx HC Rich Lean

  39. Drawbacks of current TWCs A/F A/F Active system Inactive system Need A/F close to the stoichiometric value 2CeO2 CeO2-x + x/2 O2 CeO2 is an oxygen buffer

  40. Drawbacks of current TWCs Low activity below 300 - 400 °C Solutions: • Active catalyst at low temperature • Close Coupled Converter (high thermal stability)

  41. Aging effects Sintering and encapsulation of the noble metal Sintering of the support (loss of surface area) Reaction conditions / high temperature

  42. TWC targets • Thermal stability: Thermal stability at / °C Year • Durability: USAfrom 50.000 (1980) to 120.000 miles (2004)

  43. Effect of redox aging on temperature programmed reduction (TPR) of CeO2 and Rh/CeO2 190 m2 g-1 Fresh and aged Rh2O3 reduction < 10 m2 g-1 Hydrogen consumption / a.u. Loss of surface area = • Loss of OSC/activity • Loss of metal-support interaction 190 m2 g-1 < 10 m2 g-1 Temperature / °C

  44. Why CeO2-ZrO2 solid solutions ? High thermal stability (ceramic materials) incorporation of CeO2 in the solid solution may prevent the undesirable fixation of ceria in the 3+ state such as in CeAlO3 or Ce2(CO3)3.

  45. Temperature programmed reduction of 0.5% Rh/CeO2-ZrO2 Ce4+ Ce3+ % CeO2 Rh2O3 10 20 30 40 50 50 60 70 80 90 100 Surface area < 1 m2/ g Bulk effects Hydrogen Consumption / a.u. Tetragonal Cubic 300 500 700 900 1100 1300 P. Fornasiero et al., J.Catal., 151 (1995) 168. Temperature / K

  46. EXAFS analysis of Ce0.5Zr0.5O2 Ce - O = 2.31 Å (8) Zr - O = 2.13 Å (4) = 2.34 Å (2) > 2.62 Å (2) Ce Zr O

  47. CeO2-ZrO2 structure CeO2CeO2-ZrO2 ZrO2 CeZr O

  48. M-O bonds by Raman and EXAFS spectroscopy Zr--O cubic phase F2g mode C.N. = 8 t",t' phases 4 bands (?) C.N. = 4 + 2 t' phase A1g+3Eg+2B1 C.N. = 4 + 4 CeO2 Ce0.7Zr0.3O2 Ce0.5Zr0.5O2 Ce0.2Zr0.8O2 Raman intensity / a.u. Raman shift / cm -1

  49. Temperature programmed reduction of high surface area samples Ce0.5Zr0.5O264 m2/g 10 m2/g Rh(0.5%)/Ce0.5Zr0.5O252 m2/g 17 m2/g fresh aged fresh aged O2 at 700 K O2 at 700 K P. Fornasiero et al., J.Catal., 167 (1997) 576.

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