Chemistry of catalytic converter cleaning?

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Seems like there are a lot of purported ways to clean a catalytic converter (lacquer thinner, dish soap + water, etc.). The discussion I've seen seems to focus on which methods do or don't restore efficiency in the short term. That's great, but what I want to know is which treatments might or might not chemically interact with the catalyst in a bad way. Anyone have any thoughts and/or resources on this?

If I do this, it'll be with the cats off the car, so I'm not looking at fuel additives.
 
As much as it pains me to even say his name, Scotty Kilmer has a vid. That's all I've ever watched about cleaning cats so that's the extent of my knowledge
Came across that. Avoiding it. The fact that I don't know anything about this topic makes me leery of anything he says on it (I wouldn't be able to separate fact from fiction myself).
 
If a catalyst has deposits in the first place it usually means that the catalyst is shot, the whole point of the catalyst is to burn up incomplete combustion byproducts, if you're getting deposits on the cat, it's probably poisioned and operating poorly anyways if cleaning it clears a code it'll probably come back sooner rather than later, you'll likely just end up doing it twice, once to take the bad cat off and try to "clean" it, a short while later you'll have to drop it again and replace it, might as well just bite the bullet the first time.
 
My car has 4 cats and they have to be able to withstand a good amount of heat. “Biting the bullet” is not trivial. >$3k for a good aftermarket option, >$5k for refurbished OE.

Dropping the exhaust, by contrast, is not hard (I can do it alone on my back if necessary), and I’ll probably have to do it once soon anyway and probably again in the next few years for other maintenance/repairs.

Right now there’s no urgent need to do anything about my cats AFAICT. I’m trying to stay ahead of it. If there’s something relatively simple I can do to extend their service life, it’s a no-brainer. If not, NBD.
 
After properly warming your car, run at 3/4-4/5 of your redline at highway speeds (shift to appropriate lower gear as to not exceed speed limit) for 5 miles followed by 5 runs full throttle to redline at a lower gear, coasting back down each time, then 5 more steady miles at high engine RPM's, then 5 miles in top gear (slow engine speed) at a steady 60 mph to cool everything down.
 
Yeah the best thing to do to keep your catalytic converter clean is to make sure that it actually gets all the way up to temperature or at least the best that you can get your engine up to so that it efficiently Burns off what it can. Engines that burn oil and are operated for short trips that is the hardest thing to do on one of these pieces. I didn't have my first one fail to almost 300,000 miles on my Honda Civic.
 
Seems like there are a lot of purported ways to clean a catalytic converter (lacquer thinner, dish soap + water, etc.). The discussion I've seen seems to focus on which methods do or don't restore efficiency in the short term. That's great, but what I want to know is which treatments might or might not chemically interact with the catalyst in a bad way. Anyone have any thoughts and/or resources on this?

If I do this, it'll be with the cats off the car, so I'm not looking at fuel additives.
i think about this, also about dpf.
burnt oil in cat according to some whitepaper is mostly similar to gypsum chemical mix.
reasonably diluted hcl, maybe even chlorine bleach should etch the crud on top of precious metals.
questions:
how about iron body of cat, or some types of substrates ? could be etch risk in unwanted areas
how about precious metals being flaked off by heatcycles from substrate, after many years of operation ?
I think I seen a product called Cataclean....Dont know much about it or if it works...
this is temporary, on car use. must keep using it.
similar to acetone, "oxygen carrier"and vaporisation improvement. should improve hc numbers.
 
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Yeah the best thing to do to keep your catalytic converter clean is to make sure that it actually gets all the way up to temperature or at least the best that you can get your engine up to so that it efficiently Burns off what it can. Engines that burn oil and are operated for short trips that is the hardest thing to do on one of these pieces. I didn't have my first one fail to almost 300,000 miles on my Honda Civic.

Also good to make sure that the upstream oxygen sensor is working correctly, especially on an OBD-I vehicle which may be more tolerant of a lazy oxygen sensor than an OBD-II vehicle.
 
From what I understand CAT get poisoned with glycol or melted due to excessive fuel burning through it. I don't think it is something people have been able to "clean" successfully using chemicals.
 
From what I understand CAT get poisoned with glycol or melted due to excessive fuel burning through it. I don't think it is something people have been able to "clean" successfully using chemicals.

My understanding is that it's not glycol, but the silicates in the antifreeze that poison the cat (and the oxygen sensor). Glycol itself is quite flammable and a cat will have no problem oxidizing it.

Does this mean that silicate-free antifreeze is less likely to poison a cat?
 
First off: "cleaning" the elements inside a cat should NEVER be necessary. If your engine is running properly, the OE cat should last the life of the vehicle. It's a passive unit, meaning it's functionality is directly related to the environment it's exposed to. That being said, aftermarket units are hit and miss.

Case study: my father purchased a brand new Hyundai Accent in 2018, the first year of the re-design. Within the first 5k miles it developed a misfire. Given the lack of sales of that particular model, and by extension the lack of sample size, the dealer was stumped. After multiple calls by the dealer to Hyundai corporate, it was discovered that engineering in Korea had identified that early engines were built with a bad batch of spark plugs early in the production run. The dealer replaced the plugs, and all seemed fine.

Around 30k, the car threw a P0420 code for cat efficiency. Obviously, it was covered under warranty, but it goes to show how quickly even the best OEM cat can be ruined by a poor running engine.

I've long touted the "Italian tune up" to my customers for this very reason. Many parts on modern automobiles work best when used to their full potential, and a convertor is no different. They require heat to function at their peak. I firmly believe that every car on the road would benefit from a weekly full-throttle on ramp run. Doing so allows the convertors to ignite, clears carbon, and heats the crankcase to a level which evaporates built up condensation.

Many of the issues I come across at the shop can be directly attributed to a given vehicle being "babied". Internal combustion engines do NOT respond well to repeated low load, low temp conditions. I sincerely believe my aggressive driving habits have a major influence over the fact that my 240K mile Jeep 4.7 use NO oil over the course of a 5k mile OCI. That's almost unheard of from that engine.

Load + heat = longevity.
 
Seems like there are a lot of purported ways to clean a catalytic converter (lacquer thinner, dish soap + water, etc.). The discussion I've seen seems to focus on which methods do or don't restore efficiency in the short term. That's great, but what I want to know is which treatments might or might not chemically interact with the catalyst in a bad way. Anyone have any thoughts and/or resources on this?

If I do this, it'll be with the cats off the car, so I'm not looking at fuel additives.
What effect are you trying to get, and what issue are you trying to resolve?

Catalytic converters have a wash coat of precious metal on a substrate.

The wash coat on a high surface area substrate gives it lots of area. Like the surface area of a football field in a few grams of material.

The tiny dispersed bits of PM can get covered, melted, agglomerated, reacted, etc.

Anything you seem to look at would wash soot or other chemical residues off. Not sure if much else.

Id try to reduce the catalyst in a hydrogen environment….
 
If you already drive it like an M3, I don't think there is much else you can do. I don't know about that generation of BMW, but, many cars I see only monitor the front cat's efficiency, so you may only need to replace 2 of the 4 if there is an issue. I seem to recall that those engines use oil, so the cats may just become less effective over time.

Also, I want your car. I test drove a CPO '08 M3 6MT Sedan in 2010 as a potential replacement for my '06 6MT G35 Sedan, which already had over 100K miles on it. I immediately fell in love with the engine/transmission combo, but I was concerned about operating costs while driving the miles per year that I was doing. Shortly thereafter, I dropped to a more reasonable driving schedule and bought a 3rd car, so the M3 probably would have been fine as my garage queen. I've always kind of regretted that decision. On the other hand, the G35 is still fun and fairly inexpensive to over maintain. But that 8,300 rpm V8...
 
What effect are you trying to get, and what issue are you trying to resolve?

Catalytic converters have a wash coat of precious metal on a substrate.

The wash coat on a high surface area substrate gives it lots of area. Like the surface area of a football field in a few grams of material.

The tiny dispersed bits of PM can get covered, melted, agglomerated, reacted, etc.

Anything you seem to look at would wash soot or other chemical residues off. Not sure if much else.

Id try to reduce the catalyst in a hydrogen environment….
Yeah the whole idea of cleaning the substrate is a bit odd to me but I'll admit I don't understand it completely. When we cleaned our platinum labware in school we just heated it red hot in a flame and any contaminates were burned off. That catalyst should be operating at a temperature that would accomplish the same thing, if it is not then I'm guessing something else is wrong.
 
is love to see an objective, results based test of catalyst cleaning.

in our older aircraft, the ozone converters were simply catalytic converters with a metal substrate with (I think) a sliver and manganese coating. (That’s by memory, so don’t hold me to it. Long time ago)

they were cleaned on a set hourly schedule by spraying some foofoo spray in them, then boiling in a mild solution of citric acid and water.

it seems the process works fine for O3 to O2 converters.
 
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