Since the 1970s, the federal government has taken a special interest in reducing the emissions produced by autos and trucks. In most US States, a car inspection (typically required yearly) tests not only your cars road-worthiness, but the function of your car in reducing emissions which could potentially damage the environment.
It is important to keep your catalytic system in good working order as part of the overall exhaust health of your car. Not only can a failed or dirty converter lose its effectiveness in reducing harmful emissions, it can reduce the performance of your car. Your converter may become clogged by gasoline additives in the fuel used to run your car; these additives may come from improperly deleaded gas, or additives used in certain brands of gas to increase engine performance.
Signs that your converter unit requires maintenance may include: Changes in performance of your vehicle, such as sluggish operation. Your car may lose its ability to accelerate when you push the gas pedal to speed up. Another good sign that your system needs maintenance is a big change in your gas mileage.
Typical car engines release a few chemicals into the atmosphere after conversion. Before conversion, an engine releases products of combustion such as Nitrogen gas (N2), Carbon dioxide (CO2) and Water (H20). The engine releases other emissions in smaller amounts. These include Carbon monoxide (CO), Volatile organic compounds (VOCs) and Nitrogen oxide emissions (NOx emissions). With the exception of H20, all of the above chemicals pose potential hazards to environmental and human health.
Nitrogen and water are part of the earths atmosphere. Carbon dioxide is similarly part of the natural respiration process for all carbon-based life; however, too much carbon dioxide released in the air is thought to contribute to global warming.
Far more dangerous, Carbon monoxide is a poison, which in concentrated amounts can lead to asphyxiation in humans and animals. VOCs emitted by cars are released into the water table and are believed to be carcinogenic. NOx emissions are similarly undesirable, and regulated by the federal government. They contribute to smog and acid rain, which are damaging to the environment and to human and animal health.
Before emissions get to the catalytic chamber, an oxygen sensor reads output from the engine. The vehicles onboard computer can change the mix of oxygen in the engine so that more or less oxygen escapes in the emission process. This control is used to ensure that enough oxygen gets to the converter to allow the burning off of some of the chemicals (called the oxidation process). Oxygen is the key to the entire catalysis process.
The actual converter consists of ceramic beads, or a network of honeycomb structures housed in a metal body. These plates are dipped in a metal catalyst (a substance that creates a chemical reaction) such as platinum (Pt) or palladium (Pd), or rhodium (Rh). These catalysts start a chain reaction with emissions delivered by the exhaust system.
The car part called a catalytic converter is actually two types of converter in one piece of equipment. The converter reduces harmful emissions by turning them into safer compounds by means of reduction and oxidation catalysis. These are two different types of chemical reaction used to change bad chemicals into better ones.
Reduction catalysis occurs when NOx chemicals contact rhodium in the first portion of the converting process. The rhodium catalyst pulls the nitrogen from the molecule, leaving only oxygen behind (O2). The nitrogen atoms then attract to each other, and form up in pairs to form (N2).
Oxidization on the other hand, is the second part of the catalytic process. Hydrocarbons and CO2 from the fuel burning process are subjected to platinum and palladium. This transforms the previously harmful chemicals into CO, which then bonds with the oxygen left over from the first process to create CO2 (which is far preferable to its more dangerous, single-atom cousins, hydrocarbons and carbon dioxide).
While the main purpose of a catalytic converter is to protect the environment and human health, the process is not without its flaws. Although CO2 is a far safer compound than the products that come out of the engine before the catalytic process, the release of CO2 into the atmosphere is a major cause for concern with regards to environmental damage.