In the 70s, air pollution was out of control causing people to be sick, climatic issues like acid rain, and other negative effects and most of these were as a result of car exhaust and it was then that the Clean air act was passed into law in the US causing cars to begin use catalytic converter.
This catalytic converter is a chamber along the exhaust pipe of cars (this is not found in electric vehicles) and this box receives harmful gases from the exhaust and turn them to less harmless gases into the environment. In the United State, people began stealing Catalytic converters in cars from 2018, and it wondered what could be in that box that would cause people to steal it.
The catalytic converter chamber is made up of different metals including platinum (Pt), Palladium (Pd), and Rhodium. Maybe you have heard that rhodium is the most expensive metal on earth. So you then wonder why these metals are used in something that is meant to clean harmful chemicals?
First, Rhodium beongs to a group of metals (Noble metals) that are resistant to oxidation, corrosion, and heat. With this, it can withstand the condition of the exhaust, also it i a catalyst speeding up chemical reaction. In the aspect of being a catalyst, it converts gases such as Nitrogen oxides which can destroy the ozone layer to nitrogen and oxygen gas. When you see people destroying the exhaust of a car just to remove the catalytic converter or according to Nigerians the Catalyst of the car, it is because they want to sell it. In the United States, the Rhodium in an exhaust has a black market value of over $1000. This is because this metal along with the other metals in the group are rare on earth's crust.
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Talking about abundance, it is believed that all of the earth's hydrogen were created after the big bang, and were in excess as a result of the energy from the bang. Since elements are made up of nucleus, they require energy to make more nuclei and this nuclei fusion becomes more difficult as we move down the periodic table. The immense energy in the core of a star an only keep fusing elements together to form iron and can't go more than that.
Do not think all elements naturally exist from energy fusing elements because so many elements were man made. Every element after Uranium was made by man but for others, protons were added to nucleus and this was done by adding neutrons. Since neutrons don't have charges, they require less energy to stick to a nucleus but adding them can make a nucleus unstable. This is why radioactive isotopes would decay spontaneously ejecting subatomic particles and radiation. In some cases, the neutrons that have been captured can decay into a proton (beta-decay), and when these proton shows up, a new element has been born.
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To answer the question of where neutrons are being gotten from, they are gotten from stars that die off as they have lots of neutrons in them. When this happens, a nucleus grabs one neutron which decays into a proton and them becomes a heavy element and the more protons they can decay into, the more which decays into, the more heavier element they become. Neutrons can also be gotten from supernovas which are made up of lots of neutrons but then it can also be found neutron star merges.
Rhodium likely forms from these methods and this could be why they are rare because stars do not die every time, neither do mergers of neutron stars happen each time. So when next you are complaining of the catalytic converter in your exhaust being removed, remember that there is Rhodium in it and it is rare. Until car manufacturers find a better alternatives or maybe we all go to EV, we will have to battle this.
Reference
https://langleyrecyclingkc.com/how-much-rhodium-is-in-a-catalytic-converter/
https://pmrcc.com/en/news-blog/catalytic-converter-101/catalytic-converter-value/
https://www.newscientist.com/article/2323120-cosmic-dawn-ended-200-million-years-later-than-cosmologists-thought/
https://sciencing.com/parts-periodic-table-5414878.html
https://www.mpg.de/18720037/the-end-of-the-cosmic-dawn
https://theconversation.com/after-our-universes-cosmic-dawn-what-happened-to-all-its-original-hydrogen-65527
https://home.cern/science/physics/early-universe
https://www.pnas.org/doi/full/10.1073/pnas.2026110118
