Principles

"Catalytic reagents (as selective as possible) are superior to stoichiometric reagents."

"Energy requirements should be recognised for their environmental and economic impacts and should be minimised. Synthetic methods should be conducted at ambient temperature and pressure."
(Green Chemistry Principles, Dr. Paul Anastas et al)

Using Catalysts

It is not possible to overstate the importance of catalysis in the development of greener industrial manufacture. There are many advantages in developing and using catalysts for industrial reactions. Two important ones are:

  • Catalysts affect the conditions that are needed, often reducing energy demand
  • They enable different reactions to be used, with better atom economy and reduced waste

Catalyst Life Expectancy

Although catalysts take part in the reaction, they are not reactants and do not feature in the chemical equation. In practice, however, catalysts may be destroyed during product extraction, may be vaporised during use, and may require recovery.
Nitric acid is produced by the oxidation of ammonia using a platinum/rhodium metal catalyst. During operation platinum is oxidised and vaporised, and must be recovered to prevent its inclusion in the product. The development of more sophisticated catalytic gauzes, and oxidation at lower pressure, has resulted in reduced loss of catalyst. More details can be found in the nitric acid section.

The aim is always to find a catalyst that can be reused many times, though this may depend on how the catalyst is used, not just on which catalyst is used. The Turnover Number (TON) is a measure of how long a catalyst can be used before it needs replacing. A TON in excess of 1 million indicates a stable, long-lived catalyst.

photo: car   For a detailed discussion of catalysis, see the catalysis-ed site


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