What’s a Catalyst?

A catalyst is a substance that causes or accelerates a chemical reaction without itself being affected. Catalysts participate in the reactions, but are neither reactants nor products of the reaction they catalyze. Catalytic Converter is one type of catalysts.

Catalytic converters are amazingly simple devices, so it is incredible to see how big an impact they have. A catalytic converter is a device causes conversion of harmful gases into mostly harmless products. Catalytic converters were first widely introduced in American production cars in 1975. In Iran, installation of Catalysts is mandatory on the manufacturing of cars and vans, from 2004.

Without the redox process to filter and change the nitrogen oxides, carbon monoxides, and hydrocarbons into less harmful chemicals, the air quality (especially in large cities) would reach a harmful level to the human being.

Most modern cars are equipped with three-way catalytic converters. This refers to the three regulated emissions it helps to reduce. Three-way catalysts are designed to simultaneously convert three pollutants to harmless emissions:
Carbon Monoxide (CO) → Carbon Dioxide (CO₂)
Hydrocarbons (HC) → Water (H₂O)
Oxides of Nitrogen (NO_X) → Nitrogen (N₂)

Three-way catalysts will only give full conversion of each of these three pollutants in a gas stream containing a stoichiometric ratio of CO and NOx, as shown in the figure below:

Fuel impurities can also directly impact on emissions and performance of the catalyst. The quality of automotive fuels in the European Union is specified by standards developed by the European Standards Organization as the below table:

Removing a catalyst converter is illegal. If the vehicle is computer control, removing the catalyst will cause a check engine light and limp in condition which will reduce power.