A catalytic converter is everyone's friend, because it takes the harmful emissions your car produces, and changes them into less harmful gasses. So when your car generates carbon monoxide (CO), hydrocarbons (HC), and oxides of nitrogen (NOx), they'll be transformed into carbon dioxide (CO2) and water (H20) by your vehicle's 'cat'. Almost every developed country in the 21st century requires new cars to have one, and virtually all new cars in the US have had them since 1975.
The catalytic converter is integrated into the car’s exhaust system, usually connected to the manifold in modern vehicles. Other modern cars have maniverters that form part of the manifold; the reason for this lovation is that it heats up mouch more quickly, which gets the converter working sooner. It's a far cry from the old days of under-floor cats, which sat roughly beneath the front seats on the underside of the car.
Catalytic converters all work in roughly the same way. They feature a honeycomb core or matrix coated with rhodium, platinum and palladium. These metals heat up as hot exhaust gases pass over them, and cause the harmful pollutants to chemically react, turning into carbon dioxide, nitrogen and water.
As long as it remains undamaged, a catalytic converter should typically last more than 100,000 miles. The big problem for your car's cat is impact damage, be that from running over a large object or even a curb, because this can cause the matrix inside to fracture and deteriorate. . The elements will eventually break down and exit your vehicle via the tailpipe. You'll want to keep an eye on your car's oxygen sensors and fuel injectors; both fo these can result in too much unburnt fuel being sent into the exhaust, which increases the temperature and burns out or melts the converter matrix.
Try to avoid deep puddles, too, because the rapid cooling brought about by being submerged in cold water can cause the converter to fracture.
Your car's catalytic converter has no moving parts and works automatically. Exhaust gasses heat the matrix, and once it is "lit off" it causes the expected chemical reactions in all gasses flowing through it. Most OBDII equipped cars (everything made since 1996) have oxygen (O2) sensors in the exhaust systems, before and after the catalytic converter, in order to monitor it for proper function. If a scan reveals code P0420 - Catalyst System Efficiency Below Threshold it most likely means your cat is no longer performing its job and needs replacement.
How long does a catalytic converter typically last? You should expect a cat to last at least 10 years but most last the life of the vehicle - as long as it isn’t damaged in some way, as mentioned above.