2 1 9 8 1 9 8 1 1 9 8 2 1 9 8 3 1 9 8 4 1 9 8 5 1 9 8 6 1 9 8 1 9 8 8 1 9 8 9 1 9 9 1 9 9 1 1 9 9 2 1 9 9 3 1 9 9 4 1 9 9 5 1 9 9 6 1 9 9 1 9 9 8 A n n o Outline Emission characteristics and impact Three-Way Catalysts principles and targets Oxygen Storage Thermal stability Noble metal loading Gasoline vs. Diesel engine Lean NOx catalysts Particulate Conclusions Outline Nature and origin of atmospheric pollutants STATIC SOURCES: POWER PLANTS MOBILE SOURCES: AUTOMOBILES AUTOMOTIVE EXHAUST: hunburnt/partially BURNT HYDROCARBONS (HC) to be oxidized to CO 2 hcarbon MONOXIDE (CO) to be oxidized to CO 2 hnitrogen OXIDES (NOx) to be reduced to N 2 hothers: PARTICULATE, LEAD AND SULFUR COMPOUNDS Agricultur e 1% Waste 2% Other 5% CO emissions in Europe 198 Energy Industries Other 1% 14% Fugitive Emissions % Road 62% Industry 15% Agriculture 1% Waste 2% Other 6% 198: 35... km-passenger 1998: 54... km-passenger (+55%) Other 14% 1998 Fugitive Emissions % Energy Industries Industry 1% 16% Road 6% CO emissions CO (Gg) CO emissions in Europe 6 5 4 3 2 1 198 1981 1982 1983 1984 1985 1986 Energy Industries Fugitive Emissioons Industry Road Other Agriculture Waste Other TOTAL EU15 CO from transport decreased by 4%. 198 1988 1989 199 1991 1992 1993 1994 1995 1996 199 1998 Year 1
Legislation limits in Europe NO and HC emissions (g km-1) 1 8 6 4 2 192 195 196 199 1984 1988 1992 HC NOx HC+NOx 1996 2 25 Year Reduction of >98% compared to uncontrolled emissions and durability of 18. km -1 is required by 24 in US (TIER2 phase) CO 4 3 2 1 CO emission (g km-1) Cold start Greenhouse effect gases Gas ad effetto serra CO 2 Anidride carbonica: 55% Clorofluorocarburi (CFC): 21% Altri: 5% Ossido di azoto: 4% Metano: 15% Emissioni in Europa Auto 12% CO 2 n Automotive emissions significantly contribute to greenhouse effect n Vehicle consumption must decrease Average passenger car consumption (EU) Consumo medio (l/1 km) 1 9 8 9. 8.9 1 8.8 9.5 8.9 8.9 8.1 8.1.1.8 Consumo per un veicolo di 1 kg Consumo.5.2 6. 6. 6.9 6. 6.4 Emissions depend on air-to-fuel ratio (A/F) 6 1968 191 194 19 198 1983 1986 1989 1992 1995 1998 Anno High efficiency engines are needed : diesel and lean-engine (up to 35% fuel economy) A/F = 14. stoichiometric ratio (oxidants = reductants) 2
Engine emission control : Scheme of a Catalytic converter : How the exhaust is converted? Why Rhodium in the s? E F M s, p Md e- NO 2π * Oxidation Reactions: CO + ½ O 2 CO 2 "HC" + O 2 CO 2 + H 2 O Reduction Reactions: NO + ½ CO ½N 2 + CO 2 "HC" + 2 NO CO 2 + N 2 + H 2 O Catalyst: Pt (Pd) / Rh / Al 2 O 3 / CeO 2 Pt/Rh = 5/1 Rh Pd Pt nuclear charge 4d 4d 5d 1σ 1π 3
Drawbacks: Typical light-off curve for a HC emissions (g/km) Vehicle cumulative exhaust emissions: close coupled catalyst.24.16.8 engine out ULEV standard =.64 g/km.64.48.32.16 ULEV standard tailpipe emissions.. 35 15 14 6 12 18 Time into FTP (s) About % of HC is emitted during the cold start: need of minimizing heating time Properties of a suitable catalyst (year 25) Highly active Space velocity (GHSV)= 5.-15. h -1 2-5 liters of exhaust to be converted (>98%) in 1 sec per liter of catalyst Highly selective Only H 2 O, CO 2 and N 2 as products Thermally stable Working temperatures 3-11 C Long life 18. km / On-board diagnostics (OBD) Active System Pollutans conversion (%) 1 8 6 4 2 The importance of the A/F ratio: A/F A/F 12 14 16 12 14 16 HC Inactive system CO NO x ha/f varies in the engine, which affects the conversions. hbetter A/F control = high pollutant conversion. hceo 2 act as an oxygen buffer through its Ce 4+ /Ce 3+ redox couple (OSC) 13 14 15 16 Air/Fuel - OSC 4
: Role of CeO 2 n n Oxygen storage Stabilisation of metal particles n Water gas shift n Steam reforming Air/Fuel Ratio 16 15 14 Ce 2O 3 + 1/2 O 2 CeO 2 CeO 2 Ce 2O 3 + 1/2 O 2 LEAN A/F=14.6 RICH Engine emission control: On board diagnostics 13 5 8 Time (s) CeO 2 is an oxygen buffer - OSC High efficiency gasoline and diesel engines ( ) NO x storage(6 sec) reduction (1sec) concept Lean technology (Excess of air: A/F > 14.6) HC + NO x + O 2 N 2 + H 2 O CO 2 hfuel economy (15-35%) hcombustion efficiency hpower output hand it decreases CO 2 emissions hbut : 1 ppm NO, 1 ppm HC and 5-12% O 2 : extreme selectivity is needed 5
NO x -Storage - Reduction Catalysts Drawbacks of Lean technology NO x are fixed on BaO as Ba(NO 3 ) 2 under oxidizing conditions (A/C> 14.6) NO x are reduced on s under reducing conditions (A/C<14.6) hlean Burn Catalysts: g Cu/Co-zeolite catalyst: hydrothermal stability g Pt/Al 2 O 3 : narrow operating regime low N 2 selectivity - high N 2 O formation hno x /Storage/Reduction g NO x storage on support (BaO): lean g NO x reduction on s: rich sulfur tolerance of the trap BaO dissolution during the preparation Extensive research is needed Particulate matter Particulate honeycomb filter Mixture of: Solid (soot, metals, ash, minerals) Liquid (hydrocarbons, sulphuric acid,water) Variable composition Poorly reactive Diesel Filter regeneration is exothermic = thermal sintering/plugging of the filter Diesel 6
Continuously regenerating trap Pt/Al 2 O 3 catalyst PM filter AND THE FUTURE? Are the Three Way Catalysts the Solution? Improvements in durability and low NM loading are needed: Best solution available (1) NO + ½ O 2 = NO 2 (2) NO 2 +PM= CO 2 + H 2 O + N 2 Sulphur tolerance is an issue Diesel hsubstantial improvement of lean-no x technology is needed, NO x -storage/reduction catalysts being the most reliable technology hcontinuously regenerating trap appears very promising for PM removal Conclusion Auto pulita può essere costruita trasformando il carburante in idrogeno per alimentare una cella a combustibile che genera la corrente per il motore elettrico.