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Do semi tractors have catalytic converters?

I ran onto a guy who buys used cats from salvage yards and such. He showed me two huge items that I took to be semi mufflers. He said they were catalytic converters from “some big diesel truck”. I didn’t have the heart to tell him that I didn’t think that diesels have them. Am I wrong?

Your friend has been taken.

Why is he buying cats from junk yards?

Nope, you’re not wrong. You’re probably right - it’s probably the muffler.

New semi trucks have two catalytic converters.

One is called a DOC or a Diesel Oxidizing Catalyst and the other is called a SCR or a Secondary Catalyst Reduction. The DOC captures the soot from the engine and then burns the soot off. The SCR converts the NOx emissions to N. So yes, newer big rigs have catalytic converters.

The next time you see a new big rig running down the highway, look and you won’t see the chrome stacks pointing up from behind cab.


Great answer, Tester.

nowmaybe, those catalytic converters your friend has may be from a new truck that was totalled in an accident. They could also be from an old gas burning truck, or from a large class A gasoline burning RV.

He’s buying cats for their platinum, of course. At least he didn’t appear to be stealing them… He seemed to know the business, except for the two big truck items in his van. They looked like old mufflers to me, but I didn’t tell him. I suppose they could have been from a newer truck, as even a year old one could have easily had 100K miles,

He’s buying them for the platinum and palladium. What do they get for a cat off a car for recycling? $60.00-$70.00 depending on the size? Think about how much he’s getting for those huge cats from diesel vehicles!

And pick one up. The weight will tell you it’s not a muffler.


He was paying anywhere from $60 for small Taurus and GM cats up to $250 for Mercedes, and $150 each for some BMWs, which have two. At least he was paying for them, not stealing them. He seemed to know the business pretty well. Said he’d make a profit of $50 to $75 on each cat when he sold them. He had dozens of them in his van. I’d like to know where he sells them. Of course that’s a trade secret.