Catalysis
- Created by: Emily Cartwright
- Created on: 28-05-14 14:49
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- Catalysis
- In industry, use of catalysts can;
- Allow milder reactions because the catalyst speeds the reaction up, so it may be possible to use a lower temperature and/or a lower pressure
- This reduces the energy input for the process and therefore reduced cost, consumption or non-renewable fossil fuels and the production of the greenhouse gas CO2
- Allow more efficient use of resources and reduced waste
- Improve the percentage yield of a reaction by increasing the rate of the desired reaction relative to those of unwanted side reactions
- Allow milder reactions because the catalyst speeds the reaction up, so it may be possible to use a lower temperature and/or a lower pressure
- In living systems the rates of all biochemical processes are controlled by highly specific catalysts called enzymes
- Ozone Chemistry
- Ozone (O3) is a gas which is present in the upper atmosphere
- It is very important to life on earth because it absorbs UV radiation from the sun, which if it reached the surface could cause mutations leading to for example, skin cancer
- Steady state ozone concentration
- Ozone is formed by photochemical reactions in the upper atmosphere (the UV light can provide energy to initiate reactions that might not occur significantly at the earth's surface)
- O2(g) ->UV O(g) + O(g)
- O(g) + O2(g) -> O3(g)
- The UV can also break down the ozone, to re-form diatomic oxygen
- O3(g) -> UV O2(g) + O(g)
- The UV can also break down the ozone, to re-form diatomic oxygen
- O(g) + O2(g) -> O3(g)
- Ordinarily the two natural processes are in balance, so that the rates of formation and breakdown of ozone are the same, and the concentration of ozone therefore stays fairly constant
- O2(g) ->UV O(g) + O(g)
- Ozone is formed by photochemical reactions in the upper atmosphere (the UV light can provide energy to initiate reactions that might not occur significantly at the earth's surface)
- Catalytic destruction of Ozone
- This steady state ozone concentration has been altered in the last century as a result of our releasing chemicals into the atmosphere which can catalyse the breakdown reaction
- The main culprits are chloroflurocarbons (CFC's) and nitrogen oxides
- Chlorofluorcarbons are chemicals which were widely used in the 20th century e.g. as refrigerants and aerosol propellants
- They were thought to be well suited to this because they are chemically unreactive, non-toxic and non-inflammable. They are also gases at room temperature and pressure but can be easily liquified by compression
- Although CFC's do not readily react under normal conditions at the Earth's surface, they can be broken down by UV light in the upper atmosphere to form Cl radicals
- CF2Cl2 ->UV CF2Cl(radical) + Cl (radical)
- The Cl radicals then act as a catalyst, breaking down ozone molecules in a chain reaction during which the Cl radicals are used up and then regenerated
- CF2Cl2 ->UV CF2Cl(radical) + Cl (radical)
- Although CFC's do not readily react under normal conditions at the Earth's surface, they can be broken down by UV light in the upper atmosphere to form Cl radicals
- They were thought to be well suited to this because they are chemically unreactive, non-toxic and non-inflammable. They are also gases at room temperature and pressure but can be easily liquified by compression
- Nitrogen Oxides
- Nitrogen oxides are formed naturally as a result of lightning acting on nitrogen and oxygen in the air
- However, the amount formed at high altitude has been greatly increased by the effect of jet aeroplane angines
- Nitrogen oxides are formed naturally as a result of lightning acting on nitrogen and oxygen in the air
- Chlorofluorcarbons are chemicals which were widely used in the 20th century e.g. as refrigerants and aerosol propellants
- The main culprits are chloroflurocarbons (CFC's) and nitrogen oxides
- This steady state ozone concentration has been altered in the last century as a result of our releasing chemicals into the atmosphere which can catalyse the breakdown reaction
- Ozone (O3) is a gas which is present in the upper atmosphere
- Catalysts in industry
- Ziegler-Natta Catalysts in polymer production
- These compounds contain metal and organic parts e.g. triethylaluminium
- These catalysts allow the polymers to pack together more densely as in the formation of high density poly(ethene)
- These compounds contain metal and organic parts e.g. triethylaluminium
- The Haber Proces
- The iron catalyst allows a lower temperature to be used
- Ziegler-Natta Catalysts in polymer production
- Biotechnology
- Enzymes are biological catalysts. They usually catalyse specific reactions and work best close to room temperature and pressure
- Catalytic Converters
- Motor vehicle engines produce a number of potentially dangerous pollutants
- Carbon Monoxide
- CO is formed by incomplete combustion of fuel
- It is poisonous as it combines with haemoglobin in the blood, preventing it from carrying oxygen
- CO is formed by incomplete combustion of fuel
- Nitrogen Oxides
- NO is immediately oxidised to NO2 by oxygen in the air. NO2 causes respiratory problems when breathed in and dissolves in water to form acid rain
- Unburned hydrocarbons
- A small fraction of the hydrocarbons in fuel may not burn in the engine. Some of these are carcinogenic
- Photochemical Smog
- Some of the compounds in the mixture of pollutants produced by vehicle engines can react together in the presence of sunlight to produce photochemical smog
- Carbon Monoxide
- A catalytic converter is installed in the exhaust system of petrol-driven vehicles
- A catalyst comprising an allow of platinum, rhodium and palladium is laid down on the surface of a ceramic honeycomb structure through which the exhaust gases have to pass, thus ensuring a large surface area on which catalysed reactions can occur
- Carbon monoxide is removed by a reaction with oxygen and a reaction with nitrogen monoxide which both turn it into carbon monoxide
- Unburned hydrocarbons are removed by combustion, producing CO2 and H2O
- Motor vehicle engines produce a number of potentially dangerous pollutants
- In industry, use of catalysts can;
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