Why are catalytic converters becoming an endangered species? Because they contain three valuable metals - platinum, palladium, and rhodium - making them worth hundreds, even thousands of dollars, stolen or not. It's the rhodium thieves are after. It's very rare, very expensive and has some strange properties. Could there be a better time for a Dreaded Chemistry Lesson from Hell? I think not.
Hey, chemistry fans. It's time to live the good life!. I know that a distressingly high number of you who count on the regular appearance of The Dreaded Chemistry Lesson From HellTM to fill your otherwise-empty lives are probably a few days from having the DTs because I haven't done one in a while. So, as a New York humanitarian (1) it is only right that I stop churning out a stream of boring slop about COVID drugs and vaccines and get back to my roots as a chemist. It's the least I can do to appease
all both of my devoted chemistry followers. Today, we discuss rhodium – one of the rarest and most valuable of all the elements.
Chances are that you know, or have at least heard about, someone who heads out to their car, starts driving and it's not driving well, sort of like it's towing a brontosaurus on a skateboard. What happened? There's a pretty good chance that your catalytic converter is gone. As in stolen. Yes, someone pilfered the platinum, ripped off the rhodium, and poached the palladium. This is now very common. Thefts of catalytic converters increased by 325% from 2019 to 2020. Both performance and emissions suffer in the absence of this important car component. Good luck passing an inspection without one.
The real reason dinosaurs became extinct. Image credits: Maxipixel, Maxipixel, Wikimedia Commons, AllFreeDownloads.com
A recycled catalytic converter from a car, stolen or not, can fetch between $150 and $250, but converters from trucks can be worth as much as $1,500. The value is due to the rare metals needed to make the converter work: palladium, rhodium, and platinum. Most of you would probably guess that platinum is the most valuable of the metals. It's not; it's quite the opposite. The most valuable metal in a converter is (by far) rhodium; it's also the most valuable metal in the world. As of today (1/31/22) here are the prices of selected valuable metals (per ounce)
- Silver - $22
- Platinum - $1,019
- Gold - $1,796
- Palladium - $2,437
- Rhodium - $16,850
Source: Money Metals
What is so special about rhodium that makes it so valuable? To answer this question, it's time for...
But first, since they've been my DCLFH hosts for years it's time to give Steve and Irving some recognition for their service. Maybe get to know them a little? How did they end up in such a terrible place? Here are their stories:
How Steve and Irving came to be your hosts of The Dreaded Chemistry Lesson From Hell.
Steve was a blackjack dealer from Reno who was cursed with poor impulse control and a hair-trigger temper. During one night shift he was in an especially foul mood when a woman at his table said "hit me," and he did just that. Unfortunately, the woman was the wife of a beloved local pastor, which earned Steve a trip on the one-way elevator ride to the hot zone years later when he was fatally struck by a 92-year narcoleptic Uber driver in the casino parking lot.
Irving, a cantankerous New York deli manager, secured his place in the eternal broiler when his wife asked whether he would mind if she hosted an Amway event in their 500 square foot Queens studio apartment and he responded, "I'd rather burn in hell." Irving got his wish.
Now, let's get to the rhodium chemistry lesson!
Facts about rhodium:
- Rhodium is very rare. Of the 78 elements found in the earth's crust, Rh is #77, only ahead of osmium, which is in last place.
- Rhodium is a noble metal, which means it is chemically inert, like gold and platinum. Therefore, whatever tiny amount of rhodium is found on earth (1 part in 200 million) is found as the metal itself rather than a chemical compound. But there is a very rare mineral rhodplumsite, which is a complex of rhodium, lead, and sulfur with the rather odd chemical formula Rh3Pb2S2.
(Left) A 78-gram cube of rhodium is worth $1.3 million. (Right) A sample of rhodplumsite is unremarkable looking but valuable. Images: Wikipedia, Mindat
3. Rhodium's inert properties make it suitable for use in exhaust systems. It is no accident that metals like rhodium, platinum, and palladium are used for this purpose. More common metals like iron, aluminum, or copper are more chemically reactive and would oxidize (and decompose) quickly under the conditions required to purify gasoline exhaust – a temperature of about 600°F.
4. Speaking of oxidation, this is one of the two chemical reactions that these metal catalysts (1) promote:
Rhodium is responsible for reducing (removing oxygen) from nitrogen oxide pollutants like nitrous oxide, which cause smog and acid rain.
NOx + Rh catalyst -------> N2 + O2 (a reduction reaction)
Platinum and palladium are responsible for promoting oxidation reactions that neutralize the pollutants carbon monoxide and uncombusted hydrocarbons, for example, methane.
CO + O2 + Pt/Pd catalyst -------> CO2
CH4 + O2 + Pt/Pd catalyst -------> H2O + CO2
In this way, some pretty nasty pollutants are converted to non-toxic gases. It works.
5. Rhodium is badass, even more so than gold or platinum
There's noble and there's noble. All three metals are chemically inert, but gold and platinum have one notable weakness. You can boil either metal in nitric acid (pretty much nothing on earth will survive this) and they sit there laughing. But if you add hydrochloric acid you get a horrifying concoction called aqua regia (Latin for "Royal Water") they laugh no more. Aqua regia also dissolves both platinum and gold. But it doesn't touch rhodium. Rhodium is badass.
6. Rhodium forms some crazy-looking complexes with organic molecules. Here's one of them.
Neither name will be used by Wordle. Image: Wikipedia
I don't know (or care) what it is used for, but the image is interesting. Maybe a helicopter propellor? Feel free to take a guess.
What to do about protecting your catalytic converter in New York?
If you park on the street in NYC – a form of torture that is unmatched in modern society – there isn't much you can do. A thief simply crawls under your car and cuts it off. Since the current leadership in the city, such as it is, is considering treating armed robbery as a misdemeanor some joker under a car with a saw is unlikely to have much to attract much attention.
Or you could be robbed by garages (about $800/month per car in Manhattan) and protect the converter, assuming it won't be stolen in there (3). Which is worse? The math here is beyond my feeble ability.
Or you could ditch the car and ride a bike around. But the chances of getting the bike stolen range between 100% and 100%. It used to be OK to get a heavy-duty lock and fasten the bike to a tall street sign. Not any more.
Bicycle thieves in NYC have learned to detach the sign from the top of the pole. Then they lift the bike over the empty pole. Pretty clever if you ask me. Photos: EVGrieve
Let's wrap this up. I have to write some more nonsense and Steve and Irving are preparing for their next DCLFH® gig. Plus they both have HVAC duty tonight. In hell. Could be some technical challenges.
(1) A New York humanitarian is defined as someone who pushes an elderly person in a wheelchair across a busy avenue. Halfway.
(2) ACSH friend, Dr. Joe Schwarcz, Director of McGill University's “Office for Science and Society” made a very nice YouTube video about catalysts. You can view it here. OSS has a virtually identical mission to ACSH - "separating sense from nonsense."
(3) When my brother Billy lived in Manhattan he was forced to garage his car. I naively asked him how safe it was to leave his possessions in the car. His reply: "They will steal a gum wrapper."