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Catalyst: A substance, device, or person that can create or accelerate change without itself being changed.
The 3 Way catalyst in your vehicle is designed to minimize the tail pipe emissions of unburned Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx).
This is accomplished via two chemical pathways-Oxidation and Reduction. The catalyst stores available oxygen in the exhaust stream and when the available O2 meets the HC and CO, in the presence of Platinum or Palladium, the ensuing oxidation reaction breaks the molecular bonds and Carbon Dioxide (CO2) and Water (H2O) are formed and released out of the tailpipe. When the NOx molecules enter the catalyst in the presence of Rhodium they are reduced to Nitrogen (N2) and Oxygen (O2).
It is not uncommon to see high mileage vehicle catalysts operating at or above 99.8% efficiency.
Catalyst Efficiency Example: a 4,750 lb. Ford Explorer with a 4.6 liter V-8 emits about 11.4 grams of CO/hour. An uncatalyzed 50 cc four stroke lawn mower or scooter emits more than 100 times that amount/hour. (About 2.6 lbs/hr.) A two stroke weed whacker or scooter (60% of the scooters on the road are of the two stroke variety) emits even more CO/hr.
Ellwood Thompson Pop Quiz of Science: The EPA defines the full useful life of the SUV is 120,000 miles. The full useful life of the scooter is 250 hours. Which one is the Low Emitting Vehicle (LEV)?
Hint: It’s not the one parked in the designated LEV parking area.