Substances which alter the rate of a chemical reaction without themselves getting changed are called as catalysts. The amount of catalyst used for any particular reaction is generally very small as compared to that of the reactants. We have two types of catalysts namely positive catalyst which increases the rate of a reaction and negative catalyst which decreases the rate of a reaction. In a number of chemical reactions, transition metals and their oxides are used as catalysts. Transition metals such as iron, cobalt, nickel, platinum, chromium, manganese and their compounds are the common catalysts used in various industries these days. An image of transition metals in the periodic table is given below:
Explanation for behaviour of catalyst
Transition metals show catalytic behaviour mainly due to the following reasons:
- The presence of vacant d orbitals.
- They have the ability to exhibit variable valencies.
- They have a tendency to form complex compounds.
Transition metals form unstable intermediates with their reactants as they have a tendency to exhibit variable valency and form complexes. The unstable intermediate formed during the reaction provides an alternative path having lower activation energy for the reaction. The lowering of activation energy increases the rate of the reaction. Later these unstable intermediates decompose in order to give final product and the catalyst is regenerated towards the end of the reaction. In many cases finely divided catalysts are used as they can provide a greater surface area for the reaction to take place. This large surface area actually provides free valencies through which the reactant molecules get absorbed on the surface. A large surface are facilitates more reactant molecules to move closer and get combined and hence the rate of reaction is increased
Catalysts find application in almost all the reactions that are used in industries for commercial purposes. Following are some reactions where catalysts are used:
- In hydrogenation reactions we use finely divided nickel as catalyst. The catalyst is mainly used for hydrogenating oil in order to manufacture vegetable ghee.
- In the synthesis of ammonia by Haber’s process finely divided iron is used as catalyst.
- V2O5 is used in the manufacturing of H2SO4 by Contact process.
- TiCl4 is used in the manufacturing of high density polythene.
We have seen the catalytic property of transition elements, their uses in the manufacturing of various products and the explanation for this behaviour. For any further query on any topic download BYJU’S – The Learning App and enjoy learning.