Catalytic converter chemical reaction

A catalyst is a substance that:. Only a very small amount of catalyst is needed to increase the rate of the reaction between large amounts of reactants. Different catalysts are needed to catalyse different reactions. Therefore, we must also consider the energy heat transfer across our reactor, because a catalytic converter is, in fact, a reactor.

Furthermore, each channel of the monoliths serves as a mini reactor since the reactions occur in the channels. There are three main heat transfer mechanisms in this system: 1 Heat conduction along the monolith 2 Convection heat transfer from the gaseous species to the monolith walls.

Also, reaction rates are a function of the reactants concentration so it is crucial to take into consideration their transport and consumption along the reactor. Citation: Pulkrabek, W. Download Citation. Author s : Willard W. Pulkrabek, Roy A. Affiliated: University of Wisconsin-Platteville. Preview Document Add to Cart. This process does not work if the metal is coated with lead, because lead has a high boiling point.

If the lead poisoning is severe enough, the whole converter is rendered useless and must be replaced. Recall that thermodynamics predicts whether or not a reaction or process is spontaneous under certain conditions, but not the rate of the process. The redox reactions below occur slowly without a catalyst; even if the processes are thermodynamically favorable, they cannot occur without proper energy.

A catalyst aids in the thermodynamic process by lowering the activation energy; the catalyst itself does not produce a product, but it does affect the amount and the speed at which the products are formed. Due to the precious metals in the coating of the inner ceramic structure, many catalytic converters have been targeted for theft.

The converter is the most easily-accessible component because it lies on the outside and under the car. A thief could easily slide under the car, saw the connecting tubes on each end, and leave with the catalytic converter.

Although the catalytic converter has helped reduce toxic emissions from car engines, it also has detrimental environmental effects. In the conversion of hydrocarbons and carbon monoxide, carbon dioxide is produced. Carbon dioxide is one of the most common greenhouse gases and contributes significantly to global warming. Along with carbon dioxide, the converters sometimes rearrange the nitrogen-oxygen compounds to form nitrous oxide. This is the same compound used in laughing gas and as a speed enhancer in cars.

As a greenhouse gas, nitrous oxide is a times more potent than carbon dioxide, and contributes proportionally to global warming. Introductio n Catalytic converters were first widely introduced in American production cars in due to EPA regulations on toxic emissions reductions. Dangers of pollutants Without the redox process to filter and convert the nitrogen oxides, carbon monoxides, and hydrocarbons, the air quality especially in large cities becomes harmful to the human being.

Catalytic inhibition and destruction The catalytic converter is a sensitive device with precious metals coating the inside. Lead: Most vehicles run on unleaded gasoline, in which all the lead has been removed from the fuel. However, if lead is added to the fuel and is burned, it leaves a residue that coats the catalytic metals Pt, Rh, Pd, and Au and prevents contact with the exhaust fumes, which is necessary in performing the necessary redox reactions.