The Unsung Heroes – Catalytic Converters

Hey guys! I wanna say Happy New Years! This is the first “Scientific Saturday” of the year and hopefully, I’ll actually stick to a schedule so there are more posts! Also, I’ll be taking requests if anyone is interested!

Welcome back to another brilliant “Scientific Saturdays” and today, we’ll be talking about some chemistry that helps our planet survive. This type of machine helps prevent acid rains as well possibly preventing death. That’s right! I’ll be looking at some sweet, sweet catalytical converters! Today’s blog will be concerning catalytic converters (and why you, if you drive, should have one!) Let’s dive right into it!

Okay, so why should we even have catalytic converters to begin with? Like, is it necessary? Yes. Yes, it is. If you don’t think so, then you’re probably reading the wrong blog. Imagine this: you (or whoever is driving) are trying to get somewhere by car. Theoretically, you should be dispensing out from your car carbon dioxide (CO2) and water and nothing else, right? Well, theory and practice are two different things. Because of how small the space in your engine is, and thus the limited supply of oxygen in the car, what is produced is actually carbon monoxide (CO) and some water. Also, the car, because air isn’t just comprised of just oxygen, reacts with nitrogen to form some nitrogen monoxide (NO) and sometimes nitrogen dioxide (NO2). What’s the harm in all that?

Here is what happens. Any nitrogen oxide (specifically nitrogen monoxide) will react with sulphur dioxide in the air (from places like power plants) and thus forms acid rain. [1] If acid rain is formed, what happens is the acid rain can kill trees and increase the acidity of lakes, ponds or any body of water. If you don’t know, many living organisms have specific optimum pH and that’s because of the ionic bonds in the tertiary structure of an enzyme (I’ll be talking about enzymes in a different post in the future). To give you the Cliffnotes version, a change in pH changes the ionic bonds in an enzyme, thus changing the 3D tertiary structure of the enzyme and causing the enzyme to be denatured. If an enzyme is denatured, then no metabolic processes will occur (at an efficient rate to meet the demands of the organism) and thus the organism will die. Think of it this way: acid rain is an efficient method to kill fish in a slow process, as well as plants in an area. (Also, you, if you’re unlucky enough to be caught in acid rain, because acids burn, like, hard.)

Also, think about where the fuel is being burnt. Do you think there is enough oxygen at all for complete combustion to occur? Probably not. So, what happens? Carbon monoxide is formed which is dangerous to the human body. To simplify the process in the body (because this too will be in a separate blog post in the future) the ever-loving haemoglobin, which is a prosthetic group in blood, does not bind to an oxygen molecule but rather the carbon monoxide molecule. This means that the body does not receive oxygen at all, and without oxygen, our cells cannot respire. In turn, we die, which means it’s pretty dangerous. It’s pretty clear too – according to the NHS, around 25 deaths occur due to carbon monoxide poisoning [3] and according to the CDC, in 2015, USA, there had been an approximate 393 deaths. [4] So, it’s bad and should be avoidable, if we are careful enough.

Okay, that sounds bad, doesn’t it? But how will a catalytic converter help? Glad you asked!

In a catalytic converter, there are two different types of catalysts. [5] One catalyst deals with nitrogen oxide and separates the compound into nitrogen and oxygen – so this way acid rain does not form. This is a process called reduction. Another catalyst works by adding oxygen to the carbon monoxide compound, forming carbon dioxide. This is oxidation. (In my opinion, it’s a bit of a lose-lose situation with forming CO2 or keeping the CO, but I suppose it’s better to choose the lesser of the two evils, right?)

There are three main elements in a catalytic converter – platinum (Pt), rhodium (Rb) and palladium (Pd). Platinum and rhodium are known as oxidisers (which are also knowns as the reducing agent) and palladium is known as reducers (which are also known as the oxidising agent.)

 

How the oxidisers work on nitrogen monoxide: [6]

  • 2NO -> N2 + O2
  • 2NO2 -> N2 + 2O2
  • 2N20 -> 2N2 + O2

How reducers work on carbon monoxide:

  • 2CO + O2 -> 2CO2
  • Unburnt hydrocarbons + O2 + N2 -> CO2 + H20 + N2

These types of catalysts are heterogeneous catalysts – meaning they are at a different phase (aka state) than the reactants. (Think about it – carbon monoxide and nitrogen monoxide are gases, whereas Pt, Rb and Pd are metals which are solids.) The reason why these metals are heterogeneous catalysts because these are transition metals that use their d-orbitals to absorb other molecules or ions onto the metal’s surface. In turn, this weakens the internal bonds of the absorbed species – which lowers the activation energy required for the reaction. Furthermore, the products escape from the surface of the catalyst (desorb) which remains unchanged and more reactants can then be adsorbed onto the surface and so the reaction continues.

That’s pretty much the science of a catalytic converter. If, by any chance, you do not want a catalytic converter, haha, you have no choice in that matter – at least as far as I know in England. You see, according to the government [7] a car can be identified as illegal if the car originally had a catalytic converter, or if the car has failed the carbon emissions test in an MOT. Overall, that means most cars would have to have a catalytic converter to pass the MOT test, more specifically petrol cars. If anyone wished to remove the catalytic converter or alter it with a change in carbon emissions, then there are penalties because it violates the Road Vehicles (Construction and Use) Regulations (Regulations 61(7) and 61A(3)) and the Road Traffic Act 1988 (Section 42). Penalties for cars are approximately £1,000 and for vans and lorries, it is £2,500.

Either way, it is safer to be sorry in our modern society! Thanks for reading this post! Come back next time where the next post may be a bit more… addictive.

Bibliography:

[1] https://www.epa.gov/acidrain/what-acid-rain

[2] https://www.sciencenewsforstudents.org/article/explainer-co2-and-other-greenhouse-gases

[3] https://www.nhs.uk/conditions/carbon-monoxide-poisoning/

[4] https://www.cdc.gov/mmwr/volumes/66/wr/mm6608a9.htm

[5] https://www.explainthatstuff.com/catalyticconverters.html

[6] http://explorecuriocite.org/Explorer/ArticleId/4585/catalytic-converters-how-platinum-and-other-noble-metals-keep-the-air-clean.aspx

[7] https://www.gov.uk/government/publications/modifying-your-vehicles-emissions/modifying-your-vehicles-emissions-the-legal-safety-and-health-implications

By Joerel Gestopa