Three-way catalysts play a crucial role in the exhaust system of modern vehicles. Its main function is to convert harmful exhaust gases into harmless gases, thus reducing pollution to the environment. However, do you know? Three-way catalysts are not "treated equally", and they generally have four different types of codes, which are DOC, DPF, SCR and ASC. These codes not only represent the type of catalyst, but also reflect its working principle and performance characteristics. Next, let's take a closer look at these four types of codes.

1. DOC (Diesel Oxidation Catalyst) -- Oxidation Catalyst DOC is one of the earliest exhaust treatment technologies, mainly used to treat diesel engine exhaust gases. Usually the first section of the three-stage exhaust pipe, generally with precious metals or ceramics as catalyst carriers, its main role is to oxidize the carbon monoxide in the exhaust gas, as well as hydrocarbons, and convert them into carbon dioxide and water. At the same time, it can absorb soluble organic components and some carbon particles, reduce the emission of some PM (particulate matter), and oxidize the NOx into NO

2. DPF (Diesel Particulate Filter) - wall flow particle catcher DPF is a kind of exhaust treatment technology after DOC, mainly used for filtering particles of diesel engines, and the second section of the three-stage exhaust pipe. Its main role is to capture PM particles, and the reduction capacity of PM is about 90%. When the DPF device captures enough particles, in order to avoid blockage, the captured particles will be digested, and this process is called DPF regeneration. 

3. SCR (Selective Catalytic Reduction) - selective catalytic reduction SCR is one of the most advanced exhaust treatment technologies at present, mainly used for treating the exhaust gas of gasoline engines and diesel engines, and the last section of the exhaust pipe. Its working principle is that under the action of catalyst, the reducing agent NH3 is injected into the processor, so that it can reduce NO and NO2 into N2 at 290~400°C, and almost no oxidation reaction of NH3 occurs, thus improving the selectivity of N2 and reducing the consumption of NH3. It is generally used in conjunction with urea injection system.

4. ASC (Ammonia Slip Catalyst) -- ammonia oxidation catalyst A kind of diesel exhaust post-treatment, installed at the rear end of SCR, due to the possibility of urea leakage and low reaction efficiency, the ammonia produced by urea decomposition may not participate in the reaction and directly discharged into the atmosphere. The role of ASC is mainly to eliminate excess or escaped NH3: oxidize the excess NH3 to N2, N2O, NOx; at the same time, catalyze the reaction of NOx and NH3 to nitrogen N2. In general, these four coding types represent four different working principles and performance characteristics of ternary catalysts. Although they have their own advantages and disadvantages, they are all the products of continuous progress and development in order to meet the increasingly stringent environmental requirements.