Selective Catalytic Reduction
In Automotive
Zdeněk Král
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Selective Catalytic Reduction
…in general
•Wide technique of NOx removal
•Used everywhere, where NOx is produced (and undesired)
•Used mainly for exhaust gases (chimneys, exhausts, …)
•
•Selective
•We can select which molecule will be reduced (NOx, CO, CO2, SO2)
•Catalytic
•Reaction needs to be catalysed.
•Reduction
•NOx to N2
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SCR in automotive
•Reduction of NOx using reduction agent on a surface of solid catalyst in presence of oxygen
•
•Summary equation: 4NO + 4NH3 + O2 → 4N2 + 6H2O
• Other SCR reactions:
• 8NH3+ 6NO2 → 7N2 + 12H2O
•… plus many side reactions 2NH3 + NO + NO2 → 2N2 + 3H2O „fast SCR“
•
•Reduction agent
•Needed for high conversion rates
•NH3, HC (hydrocarbons)
•
diesel exhaust.png Gasoline exhaust.png
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… a bit of History
•SCR was developer for industrial applications
•70s - applied in thermal power plants in Japan
•Since 80s – widespread to Europe and USA
•
•First mobile aplications (not powerplants)
•90s Korean cargo ships (diesel engine = electric generator)
•Reason for this application - similar application as in powerplants, steady state of engine
operation
•
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How does SCR catalyst look like?
… of urea
Obsah obrázku interiér, stůl, vsedě, klávesnice Popis byl vytvořen automaticky
•Ceramics carrier with active substance
•SiC, Cordierite
•
•„Mate“
•Heat resisting dense fibers
•Spacer for thermal dilatation
•
•Metal housing
•Stainless steel
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What is the active substance?
… of urea
Obsah obrázku interiér, stůl, vsedě, klávesnice Popis byl vytvořen automaticky
•Several substances are catalytically active enough to be used for SCR
•
•Cu and Fe zeolites (Cu-SSZ-13, Fe-ZSM5)
•
•Metal oxides (V2O5)
•
•
ZSM-5 - Wikipedia SSZ-13 Zeolite
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•Mechanism is strongly dependent on exact composition of the material
What is the mechanism?
Critical Thinking Skills Seminar
7

„State of the Art“
Obsah obrázku motocykl, fotka, vsedě, motor Popis byl vytvořen automaticky
… of urea
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SCR in Automotive
Turbocharger
HOT END
Oxidation cat
DPF+SCR
SCR
ASC
COLD END
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SCR in Automotive
ASC
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NH3-SCR in Automotive
Injection of AdBlue (32,5 % solution of urea in distilled water)
•Injection (200°C): H2N-CO-NH2 + H2O → 2NH3 + CO2
•1. hydrolysis: H2N-CO-NH2 + H2O → NH3 + HNCO
•2. acid w. water: HNCO + H2O → NH3 + CO2
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