With the development of human industrial civilization, the damage to the environment has become increasingly serious, and the pollution of the atmosphere has also intensified. People gradually realize that the exhaust of automobiles is an important source of atmospheric pollution, so the treatment of automobile exhaust has become an urgent problem to be solved in the automotive industry. Through the analysis of automobile exhaust gas, it is found that CO, HC and NOx are the most serious substances polluting the atmosphere. Therefore, the treatment of automobile exhaust gas is more and more important, which has spawned an automobile exhaust gas purification device. The three-way catalytic converter is the automobile exhaust gas purification. The main component of the device. It can greatly reduce the degree of pollution of the exhaust gas to the atmosphere.
The three-way catalytic converter is the main component for exhaust gas purification treatment of fixed pollution sources of automobiles and other engines. It uses platinum (Pt), rhodium (Rh) and palladium (Pd) as catalysts to oxidize and reduce carbon monoxide, hydrocarbons and nitrogen oxides in the exhaust gas to form carbon dioxide, nitrogen and water. The result of purification. Its purification efficiency is very high, and it can purify more than 90% of harmful substances. As people's attention to the environment has increased, countries and regions have developed increasingly stringent emission regulations, and this component plays a pivotal role in post-discharge treatment.
The three-way catalyst is generally composed of a casing, a vibration damping layer, a carrier and a catalyst coating.
The housing is made of stainless steel to prevent clogging of the carrier due to detachment of the scale. The material of the vibration damping layer is generally an expansion gasket or a wire mesh mat, which functions as a sealing, heat preservation and fixing carrier to prevent damage to the carrier caused by vibration, heat deformation and the like. The expansion gasket is composed of expanded mica, aluminum silicate fiber and a binder.
The expansion gasket expands significantly when it is heated for the first time, and only partially contracts when it is cooled, so that the gap between the casing and the carrier is completely swelled and sealed.
The catalyst carrier is typically a honeycomb ceramic material and a few metal (stainless steel) materials. The outside of the three-player catalyst is made of a double-layer stainless steel sheet. In the double-layer sheet sandwich, a heat insulating material---asbestos fiber felt is installed. The interior is filled with a scavenger in the middle of the mesh partition
purifier:The scavenger consists of a carrier and a catalyst. The carrier is generally made of alumina, and has a spherical polygonal shape and a mesh separator.
Catalyst coating: mainly composed of Pt (platinum), Rh (铑), Pd (palladium) and cocatalyst CeO2 (cerium oxide), oxidation catalyst γ-Al2O3 (aluminum oxide), coated in the carrier On the inside wall. Its rough porous surface can greatly increase the actual catalytic reaction area of ​​the carrier wall. The main role of the promoter is to improve the activity of the catalyst and high temperature stability.
1. Fuel requirements The fuel used by the vehicle must be lead-free clean fuel. After the lead-containing oil is burned, the lead particles will be covered on the surface of the catalyst when the exhaust gas is discharged through the three-way catalyst, so that the catalytic action area is reduced, thereby greatly reducing the conversion efficiency of the catalyst. This is commonly known as the three-way catalytic converter. Lead poisoning. Low-quality fuel is also one of the main reasons leading to the shrinkage, sintering and clogging of the three-way catalyst. There are also requirements for the content of impurities such as sulfur and phosphorus in gasoline.
2, the use of three-way catalytic converter must be used simultaneously with the closed-loop EFI engine. In order to maintain a relatively high conversion efficiency, the engine theoretical air-fuel ratio is 14.7:1.
3, temperature requirements The optimum operating temperature of the three-way catalytic converter is between 500-8500, the temperature is too low, the conversion efficiency of the three-way catalytic converter is low, and the temperature is too high, so that the catalyst is deactivated and the catalyst carrier is sintered.
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