SCR+ASC

1. SCR (Selective Catalytic Reduction)
1. Function
Core goal: Convert nitrogen oxides (NOx) in exhaust gas into harmless nitrogen (N₂) and water (H₂O).

Applicable scenarios: Diesel vehicle exhaust treatment to meet the NOx limit requirements of National VI/Euro VI emission regulations.

Key input: Urea aqueous solution (AdBlue, containing 32.5% urea) needs to be added as a reducing agent.

2. Working principle
Urea injection: Urea solution is sprayed into the exhaust pipe and hydrolyzed at high temperature to generate ammonia (NH₃).

Catalytic reduction: NH₃ undergoes a selective reduction reaction with NOx on the surface of the SCR catalyst to generate N₂ and H₂O.

Catalyst type: Vanadium-based (V₂O₅-WO₃/TiO₂) or zeolite molecular sieve (such as Cu-ZSM-5).

2. SCR+ASC (SCR + Ammonia Escape Catalyst)
1. Function
Core goal: On the basis of SCR, further eliminate unreacted residual ammonia (NH₃ escape) to avoid secondary pollution.

Additional functions:

Oxidation of residual NH₃ to N₂ and H₂O;

Some ASCs have the ability to oxidize both CO (carbon monoxide) and HC (hydrocarbons).

2. Working principle
Location: ASC is located downstream of the SCR catalyst.

Catalytic oxidation: Use precious metal catalysts (such as Pt/Pd) to selectively oxidize escaped NH₃ to N₂ instead of NOx.

Anti-overoxidation: The reaction conditions need to be precisely controlled to avoid excessive oxidation of NH₃ to generate NOx.