Catalyst

The automotive catalyst is equipment exhaust emissions that arise due to imperfections of the combustion process. The catalyst converts the chemical reactions using harmful substances into water, carbon dioxide and other less dangerous substances.

The primary task of the catalyst is to convert hydrocarbons, carbon monoxide and nitrogen oxides, which are produced by the engine into less harmful substances - water vapor, carbon dioxide and nitrogen. The name comes from the Greek catalyst katalýtis that indicates the substance entering into chemical reactions, the chemical reaction speed, but it will itself unchanged. In our case, the catalyst for the chemical reaction layer of precious metals. Use of catalyst in the exhaust system requires the use of unleaded gasoline, because lead destroys the catalytic effect of rare metals.

Automotive catalytic converter contains precious metals deposited on the surface reaction medium, usually used platinum compounds (oxidative part) and rhodium (reductive part). Carrier has a fine structure similar to bee plástvím that even with the compact size guarantees a large catalyst surface. At temperatures from 300 to 600 ° C, chemical reactions occur that reduce the amount of harmful ingredients. First, platinum and rhodium break down nitrogen oxides to nitrogen (N) and oxygen (O) and then platinum and palladium combine oxygen with carbon monoxide and hydrocarbons. The result is non-toxic carbon dioxide (CO ₂₎ and water (H ₂ O). Currently, the catalyst can remove 97% of hydrocarbons, carbon monoxide, 96% and 90% of nitrogen oxides.

Video:

During cold start is not an effective catalyst, begins to run from the temperature of about 300 ˚ C. To achieve this temperature, some time is needed in order to shorten this time, it is necessary to include into the exhaust system předkatalyzátor smaller in size, which is located closer to the engine. This catalyst is smaller and is located close to the manifold, so it reaches operating temperature much earlier.

exhaust pipe - předkatalyzátor

Principle:
Catalyst (more correctly: the catalytic converter) is a component of the exhaust pipe. It consists of the so-called lambda probe and subsequent catalytic equipment itself. Lambda probe responds to the composition of flue gas and is particularly important in three-way catalysts, see below.

Conventional engines burning hydrocarbon fuel combustion have imperfect, so when they run generated noxious gases - emissions . For example. carbon dioxide (CO _2), water (H ₂ O), carbon monoxide (CO), irritable nitrogen oxide (NOx), unburnt carcinogenic hydrocarbons (HC), sulfur oxides (SO _x), where diesel engines are formed solid particles (DPM) . The production of these undesirable gases affects the quality of combustion, ie the state of the engine, its mode of operation, quality and purity of the fuel, etc. The catalyst helps to significantly reduce emissions of harmful exhaust gases.

Catalyst is filrt! The catalytic chamber through ceramic honeycomb exhaust gases, which are covered with precious metals. Thanks to these metals occur chemical reactions that help break down pollutants into harmless substances. Cleaning the exhaust gas catalytic converter consists of two basic processes (chemical reactions) reduction (oxygen compounds are removed O ₂₎ and oxidation (oxygen compounds is supplied O _2).

Reduction
in reducing the nitrogen oxides NO _x changes (reduces) the N ₂ nitrogen and carbon dioxide CO _2.

Oxidation
during the oxidation of carbon monoxide is converted into CO (oxidizes) to carbon dioxide CO _2, hydrocarbons HC also oxidize water to H ₂ O and carbon dioxide CO _2. It is basically for additional burning.

Distribution of catalysts
In practice, the most commonly used catalysts for the division two-way and three-way. This meant the number of basic pollutants catalyst is able to efficiently dispose of (CO, HC and NOx). We may also share catalysts on ceramic and metal.

Two-way oxidation catalyst reduces emissions of carbon monoxide (CO) and unburned hydrocarbons (HC). Prerequisite for the correct function is sufficient oxygen in the flue gas.

Three-way (three-way) catalyst in contrast to two-way also reduces emissions of nitrogen oxides NO _X. Three-way catalyst can function properly only in a narrow range of fuel-air ratio in the box. That the motor could move in that window, you must use a feedback loop to control the fuel mixture with a lambda probe . In this way, now working all modern engines with fuel injection. Lambda probe through the engine control computer simply adjusts the ratio of fuel and air to the engine in optimum working regime of the stoichiometric mixture. Therefore, installation of three-way catalytic converter to the engine with carburetor can never bring the desired result.

Ceramic catalysts are ceramic insert. The only advantage of these catalysts is slightly lower price. Ceramic catalysts are much more sensitive to both mechanical damage (strikes a foreign object on the road) and chemicals, especially in poor adjustment. Ceramic catalysts are not suitable for modified cars on alternative fuel LPG / CNG or in diesel engines.

Metal catalysts have a metal insert. These catalysts are less susceptible to mechanical damage, not so much worse than the risk of damage due to engine operation. Metal catalysts are suitable for petrol and diesel engines and engines powered by alternative fuel LPG / CNG.

History:
The first catalyst was installed in a Cadillac already in 1975. P rvní serial car equipped with a partial catalyst became Cadillac Seville. This catalyst to some extent reduced the content of harmful substances in exhaust gases, but the first real catalyst was invented by a team of scientists led engelhardských John J. Mooney and Carl D. Keith in 1979. A year later it was improved and was called three-way catalyst.

Cadillac Seville, the first car with a catalytic converter

What You Did not Know:

How big is the active catalyst surface?
The internal structure of the catalyst is similar to a honeycomb, which allows to maximize the active area while maintaining a compact size. In the case of an ordinary engine 1.8 cc catalyst surface is approximately comparable to the area of two football pitches

How to recognize a defective catalytic converter?
According to the manufacturers of catalysts may be symptoms of a faulty catalytic converter include:
▪ odor resembling rotten eggs remaining long after the engine warms up
▪ difficulty starting the vehicle
▪ poor acceleration
▪ loss of power of approximately 80 km / h and higher gasoline consumption
▪ Knocking noise under the vehicle during acceleration.

What can destroy a catalytic converter?
▪ physical damage, such as a retarder or in the field
▪ accidental use of leaded gasoline, or use of additives containing lead
▪ catalyst may be contaminated with phosphorus, which is produced when the vehicle consumes more than one liter of oil per 1 000 km, phosphorus blocks the active catalyst layer
▪ is very dangerous contact with a catalyst nespáleným fuel. This may occur for example when there is a problem with the ignition system when the vehicle or roztlačeno Resize the heated engine, when the mixture is affected by poor maintenance of the intake system (dirty air filter or intake manifold), or when a fault occurs lambda probe. If the catalytic converter gets burnt mixture that burns in him, sharply increases the temperature in the catalyst. If the temperature exceeds 1400 ° C to destroy the catalyst.

Catalytic converter for diesel engines
Diesel engines operate with excess air (λ> 1) and therefore can not regulate the proportion of oxygen in the fuel-air mixture. Cleaning the exhaust combustion takes an additional oxidation catalyst. The additional combustion (oxidation) is used residual oxygen in the exhaust gases, thereby reducing the content of hydrocarbons (HC) and carbon monoxide (CO). The case of diesel engines is not controlled cleaning of exhaust gases and the oxidation catalyst converts only those components of the exhaust gases which can be changed by oxidation.

The amount of nitrogen constituents is not possible in an oxidation catalyst to change. The resulting oxides are therefore already reduced during combustion using a recirculation system, which means that introducing a controlled exhaust gases back into the combustion chamber. Cooled exhaust gases are fed back into the combustion chamber, and thus reduces the emissions of NO _X. If combustion at low excess air, increases in the proportion of exhaust carbon monoxide (CO), hydrocarbons (HC) and particulate matter (PM). Particles of soot (PM) can capture a special filter (DPF) .