Catalytic Converter

vehicles with internal combustion engines - come with catalytic converters - reduce pollution they produce

Converter → located midway in the exhaust system of a vehicle → between engines and the muffler.

contains coating of catalysts → made up of platinum, palladium, rhodium that speed up conversion of harmful substances in the vehicle exhaust into less harmful substances. catalysts are arranged in honeycomb structures that maximise surface area for gases to interact with.

gases that leave engine typically contain following substances:

• carbon dioxide
• carbon monoxide
• nitrogen $N_2$
• nitrogen dioxide
• nitrogen monoxide
• oxygen
• unburn hydrocarbons
• water vapour $H_{2}O$

nitrogen monoxide, nitrogen dioxide, carbon monoxide → air pollutants.

• catalytic converters can remove them by catalysing the following redox reactions:

carbon monoxide + nitrogen monoxide → carbon dioxide + nitrogen $2CO(g)+2NO(g)\to 2C{O}_2(g)+N_2(g)$

carbon monoxide + oxygen → carbon dioxide $2CO(g)\to O_2(g)+2C{O}_2(g)$

nitrogen dioxide → nitrogen + oxygen $2N{O}_2(g)\to N_2(g)+2O_2(g)$ octane + oxygen → carbon dioxide + water vapour $2C_8{H}_{18}(g)+25O_2(g)\to 16C{O}_2(g)+18H_{2}O(g)$

even though catalytic converter → increases amt of carbon dioxide in exhaust emissions → it is still preferred air pollution control original pollutants from engine are more harmful than carbon dioxide. hence, catalytic converter reduces pollution, but doesn’t eliminate it

redox reactions

Sample

lean burn engine runs with higher ratio of air to fuel than normal car engine. explain how this will affect amt of CO and NO produced compared to normal car engine

• lower compared to normal car engine
• lean burn engine has higher ratio of air to fuel compared to normal car engine. thus more oxygen is available for combustion in a lean burn engine
• hence favouring the production of carbon dioxide instead of carbon monoxide thus the amt of carbon monoxide formed is lesser compared to normal car engine
• lean burn engine has a lower running temperature compared to normal car engine. thus the probability of nitrogen gas react with oxygen gas to produce NO is lower in lean burn engine as this reaction only occurs at high temperature.
• hence amt of NO produced is lesser compared to normal car engine