Ok, since there seems to be some confusion on how a Catalytic Converter works, and why its important I figured I'd do a write up explaining the engineering behind it.
What is a Catalytic Converter ("cat")?
Its an emissions control device that is designed to remove Carbon Monoxide (CO) from the engine exhaust and convert it to Carbon Dioxide (CO2). Carbon Monoxide
is one of the gasses responsible for the 'greenhouse effect'
, believed to be responsible to global warming, but thats a topic for a different thread.
Carbon Monoxide has one carbon triple bonded to one oxygen molecule, and it looks like this:
This triple bond is typically very hard to break. CO becomes a problem because it can react with a series of other contaminents in the atmosphere to reduce the quality of the air we breath everyday.
Why do Jeep's make CO?
CO is a byproduct of our engines due to incomplete combustions (burning fuel), and since the typical gasoline engines are only around 25% efficient, there is a lot of CO produced. Multiply that by millions of cars, trucks and engines in the world, and you can see how we get trillions of tons CO produced every year.
The important part: How a Cat works
The catalytic converter works on a principal of a catalyized reaction - meaning an intermediate step is used to convert something to something else. For example - if you want to bring a box full of tools up to the 15th floor of a building, you could climb the stairs carrying the bucket, and it would take a lot of effort. However, if you take the elevator it takes a lot less effort, and you get there faster. In this example, the elevator is a catalyist that helps you get to the 15th floor.
The Cat in a vehicle converts Carbon Monoxide to Carbon Dioxide. Why do you want this to happen? Well Carbon Monoxide is a pretty nasty gas, but carbon dioxide is much better. Plants can use CO2 for energy, and they spit out oxygen when they're done...oxygen we can breath.
: Cats typically contain a Platinum. Platinum has a unique property of allowing CO to bind to its surface, and then when an oxygen molecule comes close to that CO molecule, it coverts them to CO2.
CO + * <--> CO(ad)
O2 + 2* <--> O2, (ad) --> 2 O(ad)
O(ad) + CO (ad) <--> CO2 +2*
* denotes a free adsorption site on the surface of Platinum.
The key to this reaction is it must occur above 500 Kelvin (440 degrees F), and this reaction only occurs on the surface of Platinum. This is why catalytic converters are always mounted in close proximity to the engine's exhaust manifold - where exhaust gasses are the hottest directly from the combustion chamber. This is also why they have a honeycomb inside - it increases the surface area, resulting in a significantly increased number of reactions that can occur.
Why is all this important?
If the cat is not mounted where it can operate at 450+ degrees F, its essentially useless and turns into a restriction on the exhaust system. If its operating properly, the heat and high velocity of exhaust gasses will keep exhaust flowing and will reduce CO emissions in the process. In fact, an catalytic converter that is properly placed and sized for the engine will present very little resistance to exhaust flow. A correctly installed cat will NOT reduce horsepower or torque for 95% of Jeep street use, and it is required by the government in all 50 states and most industrial countries overseas!
Basic Solid State Chemistry
The Physics and Chemistry of Materials