However, this process could be reversed by running the engine at a high temperature to increase the hot exhaust flow through the converter, melting or liquefying some of the contaminants and removing them from the exhaust pipe. 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.
As the number of cars throughout the world increases, further cuts in pollution per vehicle are needed to keep improving air quality. Many governments in the fast growing emerging markets of Brazil, India, and China — the BRIC countries —, are putting legislation in place to catch up with the standards already implemented in the US, Europe and Japan.
As exhaust gasses pass through the catalyst a chemical reaction occurs which converts carbon monoxide CO , hydrocarbons HC and oxides of nitrogen NOx to less harmful compounds water, nitrogen and carbon dioxide. To work most effectively, a catalytic converter needs to reach an optimum temperature.
It may not reach this in a short journey. Devises to pre-warm the catalyst are being developed which improve the overall performance of catalytic converters. However, they also result in an increase in CO 2 emissions, which do not cause a problem for urban air quality, but may contribute to global warming.
Oxidation catalysts may be fitted to either petrol or diesel cars. The catalyst oxidises the pollutants formed by incomplete combustion to carbon dioxide and water, and is effective for hydrocarbons, aldehydes and carbon monoxide. However, they do not reduce NOx emissions. Carbon canisters are being fitted to petrol tanks to reduce evaporative emissions of petrol petroleum.
Vapour rises into the carbon canister, which then returns the petrol to the tank, hence avoiding a loss due to evaporation. Lean burn engines are more fuel-efficient than other engines and produce less NOx and CO, but they do emit higher levels of hydrocarbons. Close Privacy Overview This website uses cookies to improve your experience while you navigate through the website.
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