Presentation by Alagudevi. C

A catalyst is a substance that increases the rate at which achemical reaction approaches equilibrium, but is notconsumed in the process.

Catalyst affects only the rate of the reaction

Most catalysts used in industrial and research laboratories are inorganic (often organometallic) compounds.

Catalysts can:

• Make a reaction possible under achievable conditions

• Reduce the necessity of expensive & dangerous conditions

• Generate high yields and high product purity

• Reduce the amount of side-product and waste created

Catalysts can be divided into two main types

Catalysts

Heterogeneous Homogeneous

This involves the use of a catalyst in a different phase from the reactants.

Typical examples involve a solid catalyst with the reactants as either liquids or gases.

The hydrogenation of a carbon-carbon double bond

The simplest example of this is the reaction between ethylene and hydrogen in the presence of a nickel catalyst.

Ethylene molecules are adsorbed on the surface of the nickel. The double bond between the carbon atoms breaks and the electrons are used to bond it to the nickel surface.

Hydrogen molecules are also adsorbed on to the surface of the nickel. When this happens, the hydrogen molecules are broken into atoms. These can move around on the surface of the nickel.

If a hydrogen atom diffuses close to one of the bonded carbons, the bond between the carbon and the nickel is replaced by one between the carbon and hydrogen.

That end of the original ethylene now breaks free of the surface, and eventually the same thing will happen at the other end.

As before, one of the hydrogen atoms forms a bond with the carbon, and that end also breaks free. There is now space on the surface of the nickel for new reactant molecules to go through the whole process again.

The proton is the most pervasive homogeneous catalyst because water is the most common solvent. Water forms protons by the process of self-ionization of water In an illustrative case, acids accelerate (catalyse) the hydrolysis of esters:

CH3CO2CH3 + H2O CH3CO2H + CH3OH

Biocatalyst is a substance, for instance an enzyme or hormone, which initiates or increases the rate of a chemical reaction.

A biocatalyst is also known as a biochemical catalyst.

A biochemical catalyst normally an enzyme.

EXAMPLE OF AN ENZYME BIOSENSOR

◦ The most widespread biosensor today is the glucose biosensor.

◦ It is very often used to measure the glucose concentration in blood.

◦ There are quite a few enzymes which could be used as glucose detectors.

◦ The following example shows the glucose enzyme reaction with glucose oxidase.