Green Chemistry

Captures carbon dioxide from power stations and stores it away safely, instead of being released into the atmosphere. It is an immediate strategy to get rid of waste gas.

Underground porous rock can act as a sponge to store carbon dioxide gas and keep it from leaking away. It has been estimated that these rocks are capable of storing up to 500 years of CO2.

Decarbonised fuels are being developed by reforming natural gas into a mixture of H2 and CO2.

CH4 + 2H2O --------> CO2 + 4H2

The CO2 will then be separated and piped off to an offshore oilfield nearing the end of its productive life to extract the remaining fuel.

Energetic UV radiation in the stratosphere provides energy to catalyse the breakdown of ozone by chlorine radicals.

CFCl3 -------> Cl (radical) + CFCl2 (radical)

Then there are two propagation steps:

Cl (radical) + O3 ------> ClO (radical) + O2          [Propagation step 1]

ClO (radical) + O ------> Cl (radical) + O2            [Propagation step 2]

Overall: O3 + O ---------> 2O2

Another chlorine radical is produced and is free to go on and break down more ozone molecules. A single CFC can destroy 100,000 ozone molecules.

Nitrogen oxide radicals can also deplete ozone. They come from aircraft engines or lightening.

NO (radical) + O3 ------> NO2 (radical) + O2            [Propagation Step 1]

NO2 (radical) + O ------> NO (radical) + O2              [Propagation Step 2]

Overall: O3 + O -------> 2O2

CFCs have been banned almost completely and are now being replaced with HCFCs and HFCs. However, HCFCs and HFCs also contribute to global warming, and HCFCs are up to 10,000 more potent as a greenhouse gas than carbon dioxide.

A typical catalytic converter is made from platinum, palladium and rhodium supported on a honeycomb mesh. The honeycomb mesh provides a large surface area.

Oxidation catalysts are used on diesel engines to decrease emissions of carbon monoxide and unburnt hydrocarbons. The following reactions take place:

2CO + O2 ------> 2CO2

C12H26 + 18.5O2 -----> 12CO2 + 13H2O

In a three way catalytic converter, the catalyst provides a large surface area for the reaction to take place. The CO and NO gas molecules diffuse over the catalytic surface of the metal, and they are held onto the metal surface by adsorption. Temporary bonds are formed betweent the metal and the gas molecules. These bonds hold the molecules in the correct position on the metal surface, where they react together. After the reaction, the CO2 and N2 products are desorbed from the surface where they diffuse away.

2NO + 2CO ------> N2 + 2CO2