The working principle of a three-way catalytic converter:
When the high-temperature vehicle exhaust passes through the purification device, the purifying agent in the three-way catalytic converter will enhance the activity of CO, HC and NOx gases, promoting certain oxidation-reduction chemical reactions among them. Among them, CO is oxidized into colorless and non-toxic carbon dioxide gas at high temperatures. HC compounds are oxidized to water (H2O) and carbon dioxide at high temperatures. NOx is reduced to nitrogen and oxygen. Three harmful gases are transformed into harmless ones, thus purifying the vehicle exhaust.
The carrier component of the three-way catalytic converter is a porous ceramic material, which is installed in a specially designed exhaust pipe. It is called a carrier because it does not participate in the catalytic reaction itself, but is covered with a layer of precious metals such as platinum, rhodium and palladium on top. It can convert HC and CO in the exhaust gas into water and CO2, while decomposing Nox into nitrogen and oxygen. HC and CO are toxic gases. Excessive inhalation can cause death, while NOX directly leads to the occurrence of photochemical smog.
Research has proved that the three-way catalytic converter is an effective method to reduce these emissions. Through oxidation and reduction reactions, carbon monoxide is oxidized to carbon dioxide, hydrocarbons are oxidized to water and carbon dioxide, and nitrogen oxides are reduced to nitrogen and oxygen.
All three harmful gases have turned into harmless ones. The three-way catalyst needs to react at a minimum temperature of 250 degrees Celsius. When the temperature is too low, the conversion efficiency drops sharply. The active temperature (optimal working temperature) of the catalyst is around 400 ℃ to 800 ℃. If it is too high, it will also accelerate the aging of the catalyst. Under the ideal air-fuel ratio (14.7:1), the catalytic conversion effect is also good.
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