Catalytic Converter Basics...

Learning something new on the internet always starts with filtering out the bad advice and learning from the good. Can someone tell me if I'm at least understanding the basics of catalytic converters? I deeply regret not taking any chemistry in school some days.

Precious metals in a muffler-like container require heat (mainly the exhaust), a 14.7/1 air fuel mixture (well, approximately), and an exhaust free of oil, coolant and other contaminants. But it has to perform 2 separate chemical reactions - oxidation & reduction. The oxidation will remove carbon monoxide and unburned hydrocarbons by combining them with oxygen the cat has stored. The reduction will break apart the various oxides of nitrogen into oxygen & nitrogen, making them no longer a smog component. Pretty good for a simple pipe with a few special metals in it. BUT, in order for it to work, the cat requires periods of rich & lean (it will store oxygen when lean for the oxidation). So instead of getting the mixture to a 14.7/1 ratio and keeping it there, the ECU will deliberately cycle the mixture between slightly rich and slightly lean.

Before I write more (maybe a lot), do I have the basics right? No sense making you read more if my understanding is way off.

tmcquinn wrote: So instead of getting the mixture to a 14.7/1 ratio and keeping it there, the ECU will deliberately cycle the mixture between slightly rich and slightly lean.

I don't claim to understand the magic that happens in a Cat. But, it is my understanding that the Rich/Lean switching is a result of the ECU TRYING to maintain a perfect 14.7:1 ratio. Variable conditions make it impossible to maintain a perfectly solid 14.7:1 ratio. Like steering a car, to maintain driving in a straight line, the steering wheel is constantly adjusting left and right.

You’ve got the basics right