Legend has it, “Let there be catalytic converters!” said GM’s Ed Cole, and »poof« the catalytic converter sprang into existence and evolved into the kind we now use. How it actually happened is a whole lot more complicated. Kind of amazing it happened at all, actually; it almost didn’t, several times over.
The idea of catalytic cleanup of exhaust dates back a lot further than many people realise. A top catalysis expert—probably the top expert for many years—was Eugene Houdry, who devised techniques for catalytic (rather than thermal) cracking of petroleum to turn it into better and more gasoline and other useful products, and then after WWII he applied his expertise to various kinds of exhaust. At first he worked to solve specialised, local problems like how to use engine-driven forklifts and machinery in warehouses, mines, and other enclosed spaces without gassing all the workers, and how to eliminate noxious odours from factory smokestacks. But it wasn’t long before he turned his sights on automobile exhaust.
Here’s an excellent article about his work (and exhaust catalysis in general) in Popular Science, June of 1955. “One of these days,” it starts out, “you are going to take a whiff of your car’s exhaust and get a surprise; the greasy smell will be gone.” That day was quite awhile in coming; it took about two decades’ time after this article was published.(click the pic for the whole article in a new browser tab):
For 1961 the road draft tube, which dumped hydrocarbon fumes and vapours from the engine crankcase into the atmosphere, was replaced in California by positive crankcase ventilation systems that routed crankcase fumes into the intake tract to be burned. Success with that first effort was followed by experimentation with all kinds of ideas for auto emissions control. Some of them moved things in a good direction, and while their R&D paid long-term dividends in knowledge of combustion dynamics and suchlike, at the time many of them degraded drivability, performance, and fuel economy, and none of them made car exhaust enough cleaner over enough miles to meet the increasingly obvious need.
From very early on there were musings about exhaust catalysis. Despite successful demonstrations of practical catalytic converters by outside suppliers, the idea was widely unpopular with automakers, so things moved slowly until 1970, when the U.S. Congress put the Clean Air Act on the books. It mandated that emissions of three major pollutants in exhaust—carbon monoxide, unburnt hydrocarbons, and oxides of nitrogen—be cut down by 90% by the 1975 model year (versus 1970-model cars, which the industry had straightfacedly argued were clean enough that no further regulation was necessary). The law had sharp teeth, too, requiring automakers to demonstrate not just a whack of money thrown at the problem, but actual, real, ongoing good-faith effort, subject to stringent audit. Suddenly there was very urgent interest in catalytic exhaust treatment. Yes, converters would be expensive, and yes, they might have to be bought rather than made in-house, and yes, there were lots of unknowns, but y’know, ninety percent cutdown or their vehicles wouldn’t be saleable!
That brings us to the start of the catalytic converter development timeline thoroughly and engagingly described in Doing The Impossible, a 2004 deep-dive article in the once defunct, now resurrected, highly worthy magazine “Invention & Technology”. If you’ll read only one of today’s links, please make it this one. Read it now; the rest of this post will make more sense afterward (alternate and better-formatted/more readable link here archived from their old website).
Y’back! Okeh, so if catalytic converters didn’t just appear on GM’s say-so, then what was GM’s role? Well…it’s complicated. GM, by dint of their employee Thomas Midgley Jr’s 1921 discovery and their 1923 joint venture with Esso (Ethyl Corporation) were largely responsible for the existence, proliferation, and persistence of leaded gasoline, which spoils exhaust catalysts. GM sold Ethyl in 1962, and so had likely been reluctant to do something that would degrade the value of the company they’d sold—such as develop and commercialise cars that couldn’t take leaded gasoline—but the Clean Air Act came along and put push to shove about it.
A quote attributed to GM’s Cole, to the effect of ~”give me unleaded fuel and I’ll put catalysts on the cars”, when taken out of context, has a spaketh-the-Lord sound about it, and that’s probably where the idea comes from that he was the go/no-go decider for the technology and industry as a whole. He wasn’t, but he did decide to go forward with catalytic converters on GM vehicles, and he overcame inertia and resistance to make that happen. Given GM’s market share at the time, his decision and effort surely went a very long way in terms of the percentage of catalyst-equipped ’75 cars on the road, and made it easier for the rest of the industry to do it. GM’s big market share probably amounted to a critical mass of the vehicle fleet; If an AMC or a Chrysler, a VW or a Toyota had decided in favour of catalytic converters but GM had gone with some other method, it would’ve been much harder (or likely impossible) to enact the mandate for universal nationwide availability of unleaded gasoline by July of 1974 in time for the first ’75 cars to hit the roads.
So GM certainly deserves substantial credit for getting catcons onto the roads. But as to those converters themselves, well…yeah…about that. GM didn’t participate in the monolithic honeycomb converter R&D described in the linked I&T article, or avail themselves of its fruits; they wanted their own AC Spark Plug division to make their converters, and they weren’t going to use a monolithic design. GM had spent a mountain of dollars in the ’60s and early ’70s trying to develop a practical catalytic converter, and it seems some chunk of that expenditure went into flailing and failing. John DeLorean’s scathing memoir “On a Clear Day You Can See General Motors” makes a tantalising, cryptic, one-line reference: “monolithic converter—$millions wasted”. I hope someday to find an access point for that particular rabbit hole.
Here’s what you see if you peer into one end of a monolithic converter—a gazillion tiny straight-through tunnels. Hold such a converter up and you can see light coming through from end to end:
And here’s a cutaway showing how the exhaust has a relatively easy, straight flow path from inlet to outlet in such a converter:
That’s the kind GM decided against. Instead of a cordierite honeycomb for exhaust to flow through, GM went with a bed of alumina pellets or beads for exhaust to be forced through. And “force” is quite an apt word. Here’s the inlet of a GM converter; exhaust hits this wall and has to turn two sharp corners, then enter the bead bed through slotted louvers. Look closely and you can see individual beads in some of the louvers:
And at the other end of the converter, here’s the outlet—more tight corners and flow restriction. Some might remember the prominent hissing sound from the exhaust of a converter-equipped GM vehicle at high engine RPM, as when the driver would floor the accelerator. Hissing is caused by gas turbulence resulting from flow restriction. H’mm…y’think?
The beads were packed in pretty tightly, but there had to be a little wiggle room or else there’d be no flow possible. But that also meant the beads would tend to bounce around and abrade one another with gas flow and road vibration. Gradually the beads would attrit, accrete, and plug up the bead bed outlet plate, causing severe exhaust restriction. And the louvered plates containing the beads eventually tended to soften and distort, letting beads out of the bed (so much for GM’s claims that this design was superior because it allowed for replacement of just the catalyst rather than the whole assembly). Some of those freed beads were caught by the muffler downstream of the converter, but sometimes a red-hot bead managed to make it through the muffler and was ejected at high speed out the tailpipe. So heavy-duty GM vehicles—station wagons, trucks, and vans—came with a spark arrestor at the end of the tailpipe. Here’s such a one, photographed recently on a decrepit RV factory-lettered “454 SG” on the side and obviously on a Chev/GMC chassis. Someone has punched three larger holes in the outer screen, revealing the inner screen:
By and by, when enough beads plugged enough holes in the spark arrestor, the hiss grew more prominent and occurred at lower engine speeds.
Now, any kind of catalytic converter will overheat and melt down if too much raw fuel hits it. That’s why automakers installed them only in conjunction with high-power ignition systems—GM’s was especially good—and other catalyst-protection measures. But carburetors, particularly non-feedback ones, and catalytic converters were a bad marriage from the start; there were going to be rich conditions sooner and later, and the catalyst would suffer—especially at high altitude.
One morning in the mid-1980s my mother, in turn to drive the carpool, pulled her 1978 Caprice Classic into the driveway of one of my elementary schoolmate’s house to pick him up. He opened the door and we heard an alarming sound coming from under the car, like BvvFFFft!……bvvFFFft!……bvvFFFft! An exhaust leak, that much was obvious, but it didn’t sound like your ordinary everyday faulty muffler—my mother was quite adamant about that (“Shut up about the car, Daniel! I’ve had a broken muffler before! I know what they sound like, and that’s not it!”). The muffler got replaced, but the car’s original converter stayed—and wheezed—on.
In retrospect, what we were hearing was exhaust backing up behind a severely clogged catalytic converter and eventually forcing its way out, once enough pressure built up. That would also explain the eyewatering stink of its half-catalysed exhaust, which smells worse than uncatalysed or fully catalysed because it’s a fœtid mix of both. Dad’s ’77 Cutlass Supreme had the same ailment up there at 5,500 feet near Denver. It ran poorly, too, but this was the early 1980s and “clogged catalyst” just wasn’t much on the radar at that time, at least not the radar of the service stations my folks patronised. Those cars would have run a lot better with monolithic replacement converters.
But those bad ol’ bead beds were gone by 1981 and GM went to monolithic converters like everyone else, right? Actually, no. While they did begin phasing in monolithic converters in the early-mid 1980s, GM kept putting pellet-bed type converters in trucks and vans clear on up through the mid-1990s. When oxidation + reduction “3-way” converters came in for ’81, GM put two bead beds, one above the other, in the one housing. That’s twice the baffle plates, for those keeping score at home. (Sorry, what were we talking about? Oh yes: flow restriction and turbulence.)
Here’s a very detailed 1979 analysis of nine catalytic converters after what passed for high miles at that time. As today’s clickbait headlines are wont to say, Photos 10 and 19 will shock you! (Click Photo 10 here, of meltdown in a ’75 Dodge converter, to get the analysis in the background as a pdf):
Now, I’ve been plenty critical of GM here, but they’re hardly the only automaker to have faffed around with
half-melted half-baked catalytic converter systems. Ford used monolithic converters, thus avoiding the bead badness, but in many cases the inlet was at 90° to the flow axis; the exhaust hit a wall on entering the converter and had to turn a sharp, restricted corner to get into the main body. But wait, there’s more: for 1975 Ford put a catalytic converter on just one leg of the headpipe on many V8 models, thus treating the exhaust from one but not the other bank of cylinders. On learning this really happened, I was reminded of a ’75 LTD that lived in our high school auto shop’s fenced yard. We figured the single cat meant someone had repaired half of the exhaust system without bothering to replace the “other” cat, which actually wasn’t ever there to begin with. This meant different backpressure for each half of the engine even when new, let alone after some miles—small wonder cars of that time developed a reputation for running poorly.
These kinds of monkeyshines, amongst many others, paint a plausible picture of automakers indulging in a cynical effort to kill vehicle emissions and safety regulation, which many of their SAE papers of the time reveal they viewed as a needless, pointless, passing fad. And they resented being told how to make cars. They invested enormous money and effort into fighting and delaying almost each and every provision of each and every regulation. Maybe if that money and effort had been put into the cars instead, results might’ve been much nicer. But as it was, cheap and nasty compliance was one of their primary tools in the war against regulation: “Oh, gosh, Mr. and Mrs. Carbuyer, you say your new car has ugly bumpers and runs poorly and gets lousy gas mileage and won’t stay fixed and buzzes angrily at you until you put on the uncomfortable seat belts? Gee, »tsk« what an awful pity. Not our fault; the government made us do it. Guess you’d best run get busy writing to Congress!”.
It didn’t work. The catalytic converter is still with us. It’s not without baggage or tradeoffs, and here’s a biggie: most of the noble metals used in catalytic converters come from South Africa. The sudden surge in demand for platinum and palladium and eventually rhodium came at the depths of the Apartheid era, which means we got to breathe cleaner air over here by dint of vicious, brutal racial enslavement over there, ugh. But the cat does a terrific job of cleaning up engine exhaust, and is now in virtually universal use on petrol-powered road vehicles all over the world.
• New: A Catalytic Converter That Really Cleans Up Auto Exhaust (Popular Science, December 1970)
• Detroit Promises Clean-Air ’75s…But Ups the Sticker Another $300 (Popular Mechanics, September 1973—AMC, Chrysler, Ford, and GM emissions bigwigs scorn the law, ruefully resign themselves to using catalytic converters, and predict big troubles and costs)
• Mining Platinum, Palladium, Rhodium From Street Dust (Pity this wasn’t around in the ’70s and ’80s when GM’s bead converters were chuffing out catalyst dust!)
• Moving Violations: Automobiles, Experts, and Regulations in the United States (a graphic look at how the sausage was made. Includes direct accounts of some of the dramatics and disingenuous ploys the automakers tried to get the standards loosened. Relevant sample pages available online here)
• A Review And Analysis Of The Good Faith Of The Automobile Industry In Attempting To Comply With The Statutory NOx Standard (A very deep mid-’70s look at the complex matter of whether automakers were really doing their best—and if not, whether appropriate remedies were legally available)