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Q11(b):
Discuss briefly the following:
(b) Catalytic converter
Solution :
1. Definition and Primary Objective
A catalytic converter is a critical emission control device fitted into the exhaust systems of automobiles. Its primary objective is to reduce the toxicity of emissions from an internal combustion engine by catalyzing redox (reduction and oxidation) reactions. This mitigates the release of severely toxic and environmentally damaging pollutants into the atmosphere, directly addressing the issue of vehicular air pollution.
2. Structural Composition and Catalysts
The core of a catalytic converter consists of a ceramic monolith with a honeycomb structure, which maximizes the surface area available for exhaust gases to interact with the active catalytic materials. This structure is coated with highly expensive noble metals, which serve as the chemical catalysts:
- Platinum ($Pt$) and Palladium ($Pd$): These act as oxidation catalysts, facilitating the addition of oxygen to unburnt hydrocarbons and carbon monoxide.
- Rhodium ($Rh$): This acts as a reduction catalyst, facilitating the removal of oxygen from nitrogen oxides.
3. Chemical Mechanism: Reduction and Oxidation
As the high-temperature exhaust gases pass through the catalytic converter, three simultaneous, vital chemical conversions occur [Per the principles of catalytic redox chemistry]:
- Conversion of Unburnt Hydrocarbons ($HC$): Unburnt fuel residues are oxidized to form carbon dioxide and water vapor.
$C_xH_y + \left(x + \frac{y}{4}\right)O_2 \xrightarrow{Pt/Pd} xCO_2 + \frac{y}{2}H_2O$ - Oxidation of Carbon Monoxide ($CO$): The highly toxic carbon monoxide is oxidized into the comparatively harmless (though greenhouse-contributing) carbon dioxide.
$2CO + O_2 \xrightarrow{Pt/Pd} 2CO_2$ - Reduction of Nitrogen Oxides ($NO_x$): Nitric oxide and nitrogen dioxide, which contribute to acid rain and photochemical smog, are reduced to harmless nitrogen gas and oxygen gas.
$2NO \xrightarrow{Rh} N_2 + O_2$
$2NO_2 \xrightarrow{Rh} N_2 + 2O_2$
4. Schematic Representation of a Catalytic Converter
5. Operational Precaution: The Mandate for Unleaded Petrol
Automobiles fitted with a catalytic converter must operate exclusively on unleaded petrol. Historically, tetraethyl lead ($Pb(C_2H_5)_4$) was added to petrol as an anti-knock agent to prevent premature engine combustion. However, lead behaves as a catalyst poison. Upon combustion, lead is vaporized in the exhaust stream and coats the platinum, palladium, and rhodium sites in the honeycomb mesh. This irreversible physical coating blocks the active catalytic sites, entirely rendering the catalytic converter inactive and ineffective at neutralizing toxic emissions.
Final Solution: A catalytic converter is an exhaust emission control device utilizing heavy noble metals (Platinum, Palladium, Rhodium) in a honeycomb mesh to chemically catalyze highly toxic vehicle emissions (Unburnt hydrocarbons, $CO$, and $NO_x$) into harmless atmospheric gases ($CO_2$, $H_2O$, and $N_2$). It requires the strict use of unleaded petrol to prevent the deactivation of these expensive catalysts by lead poisoning.
More Questions from Class 12 Biology Environmental Issues EXERCISES
- Q1: What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.
- Q1: What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.
- Q2: List all the wastes that you generate, at home, school or during your trips to other places. Could you very easily reduce the generation of these wastes? Which would be difficult or rather impossible to reduce?
- Q2: List all the wastes that you generate, at home, school or during your trips to other places. Could you very easily reduce the generation of these wastes? Which would be difficult or rather impossible to reduce?
- Q3: Discuss the causes and effects of global warming. What measures need to be taken to control global warming?
- Q3: Discuss the causes and effects of global warming. What measures need to be taken to control global warming?
- Q4: Match the items given in column A and B:
- Q4: Match the items given in column A and B: Column A Column B (a) Catalytic converter (i) Particulate matter (b) Electrostatic precipitator (ii) Carbon monoxide and nitrogen oxides (c) Earmuffs (iii) High noise level (d) Landfills (iv) Solid wastes
- Q5(a): Write critical notes on the following: (a) Eutrophication
- Q5(a): Write critical notes on the following: (a) Eutrophication
- Q5(b): Write critical notes on the following: (b) Biological magnification
- Q5(b): Write critical notes on the following: (b) Biological magnification
- Q5(c): Write critical notes on the following: (c) Groundwater depletion and ways for its replenishment
- Q5(c): Write critical notes on the following: (c) Groundwater depletion and ways for its replenishment
- Q6: Why does ozone hole form over Antarctica? How will enhanced ultraviolet radiation affect us?
- Q6: Why does ozone hole form over Antarctica? How will enhanced ultraviolet radiation affect us?
- Q7: Discuss the role of women and communities in protection and conservation of forests.
- Q7: Discuss the role of women and communities in protection and conservation of forests.
- Q8: What measures, as an individual, would you take to reduce environmental pollution?
- Q8: What measures, as an individual, would you take to reduce environmental pollution?
- Q9(a): Discuss briefly the following: (a) Radioactive wastes
- Q9(a): Discuss briefly the following: (a) Radioactive wastes
- Q9(b): Discuss briefly the following: (b) Defunct ships and e-wastes
- Q9(b): Discuss briefly the following: (b) Defunct ships and e-wastes
- Q9(c): Discuss briefly the following: (c) Municipal solid wastes
- Q9(c): Discuss briefly the following: (c) Municipal solid wastes
- Q10: What initiatives were taken for reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?
- Q10: What initiatives were taken for reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?
- Q11(a): Discuss briefly the following: (a) Greenhouse gases
- Q11(a): Discuss briefly the following: (a) Greenhouse gases
- Q11(b): Discuss briefly the following: (b) Catalytic converter
- Q11(c): Discuss briefly the following: (c) Ultraviolet B
- Q11(c): Discuss briefly the following: (c) Ultraviolet B
CBSE Solutions for Class 12 Biology Environmental Issues
Chapters in CBSE - Class 12 Biology
- Reproduction in Organisms
- Human Reproduction
- Reproductive Health
- Principles of Inheritance and Variation
- Molecular Basis of Inheritance
- Evolution
- Human Health and Disease
- Strategies for Enhancement in Food Production
- Microbes in Human Welfare
- Biotechnology: Principles and Processes
- Biotechnology and Its Applications
- Organisms and Populations
- Ecosystem
- Biodiversity and Conservation
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