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Chemistry of Catalytic Converters
Episode 1514th June 2024 • Chemistry Connections • Hopewell Valley Student Publication Network
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Chemistry Connections

Chemistry of Catalytic Converters

Episode #15  

Welcome to Chemistry Connections, my name is Matthew Nguyen and I am your host for episode 15 called Fumes to Fresh Air. Today I will be discussing the chemistry of catalytic converters. 

Segment 1: Introduction to Catalytic Converters

General Information on Catalytic Converters

  • Used to reduce emissions from car engines
  • Used in exhaust systems to remove harmless byproducts from internal combustion engines
  • Removes nitrogen oxides, carbon monoxide, and hydrocarbons and turns them into carbon dioxide, water, and nitrogen gas
  • Converts 98% of the harmful emissions to less harmful gasses
  • Most stolen parts of the car because it has valuable materials like platinum, rhodium, and palladium which can sell for a lot of money
  • No more than 4-9 grams of these precious metals are used in a single converter
  • Located between the muffler and the engine
  • Composed of metal housing with a ceramic honeycomb-like interior with insulating layers
  1. To begin, I’ll first dive into what specifically a catalytic converter is and what its function is for those who don’t know
  2. A catalytic converter filters out harmful emissions released by a vehicle.
  3. It is a metal square box containing a ceramic honeycomb interior, located on the underside of the car between the engine and muffler with insulating layers composed of precious metals like platinum, rhodium, and palladium. 
  4. Because these metals are extremely valuable, they make the converter one of the most frequently stolen items in a car. Put a pin in that idea, we’ll come back to it later.
  5. Due to the elements of palladium, platinum, and rhodium, a single converter can filter 98% of harmful emissions like nitrogen oxide, carbon monoxide, and hydrocarbons into harmless gasses of carbon dioxide and nitrogen. 

Segment 2: The Chemistry Behind Catalytic Converters

The Chemistry part of Catalytic Converters

  • One reduction and two oxidation reactions occur inside a catalytic converter
  • Nitrogen oxide reduces into elemental nitrogen and oxygen
  • Carbon monoxide oxidized into carbon dioxide
  • Hydrocarbons are oxidized into carbon dioxide and water
  • Two systems running in catalytic converters “rich” and “lean” 
  • It runs lean resulting in the favoring of oxidation of carbon monoxide and hydrocarbons 
  • It runs rich resulting in the favoring of the reduction of nitrogen oxide into elemental nitrogen and oxygen
  • If NO is not converted into less harmful emissions, it can create smog or acid rain 
  • Catalysts like platinum, rhodium, and palladium are used to lower the activation energy to drive the reaction forward

  1. Let's pause here and talk about some of the chemistry at work. Surprisingly, catalytic converters have many chemical processes.
  2. When a car combusts in the presence of oxygen and gasoline, it releases nitrogen gas (N2) as a harmless byproduct; however, when it bonds with oxygen, it creates nitrogen oxides which are extremely harmful to the environment. If these nitrogen oxides are not filtered out, it can create smog or even acid rain.
  3. That's when catalytic converters come into play which contain no more than 4-9 grams of valuable metals like platinum, rhodium, and palladium. 
  4. What makes these metals different from others is that they are good at resisting oxidation, corrosion, and acid allowing them to withstand all of the chemicals released by an internal combustion engine. 
  5. Furthermore, these metals function as catalysts within a catalytic converter. These catalysts reduce the activation energy needed for a reaction to occur, allowing it to proceed at a faster rate. Furthermore, the honeycomb structure within a converter allows for a large amount of surface area so that multiple reactions occur rapidly and efficiently. 
  6. Inside a catalytic converter, a redox reaction occurs simultaneously: called oxidation and reduction reactions. In an oxidation reaction, electrons are lost whereas in a reduction reaction, electrons are gained. Each metal is responsible for either oxidizing or reducing carbon or nitrogen. For example, the first stage of the reaction involves platinum and rhodium which both take part in reduction reactions that reduce nitrogen oxides in the exhaust. They can do this by removing nitrogen atoms from nitrogen oxide or nitrogen dioxide molecules, freeing up oxygen atoms. Once the catalysts have finished the reaction, the nitrogen atoms react with each other creating nitrogen gas which is harmless to the environment. The byproducts are nitrogen and oxygen gas.
  7. Similarly, the second stage of the reaction involves platinum and palladium which oxidize carbon monoxide and hydrocarbons, turning them both into carbon dioxide and water. 

Segment 3: Personal Connections

  1. Let's return to the idea of how catalytic converters get stolen pretty often.
  2. Well… a couple of years ago, after coming home from a family trip, I remember my dad turning on our car after dropping it off in a secluded lot for several weeks. The car soon became extremely loud after ignition and it turns out that the catalytic converter on our car was stolen. 
  3. The reason for this was merely because of the precious metals within the converter that made it a prime target for thieves.
  4. The purpose of these metals has remained a curious phenomenon with me, but taking AP Chem has allowed me to understand the chemistry and function of the metals. This has prompted me to want to create a podcast episode about how harmful emissions are reduced and the chemistry behind catalytic converters. 

Thank you for listening to this episode of Chemistry Connections.   For more student-run podcasts and digital content, make sure that you visit


Music Credits

Warm Nights by @LakeyInspired 

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