A chemical reaction is a process by which atoms of the reactants come together and combine or re-arrange to form products. An example of a chemical reaction is the reaction of nitrogen gas and hydrogen gas to produce ammonia:
`N_2 + 3H_2 -> 2NH_3` . This is an example of the former where atoms combine. The oxidation of methane to form carbon dioxide and water is an example of the latter.
For chemical reactions to occur, there are some factors that should be considered. For instance, the reactants must come together - must collide. The collision must also happen with the reactants assuming a specific orientation, and the collision must occur with the reactants having enough energy. All these factors contribute to the energy barrier, known as activation energy, of chemical reactions. Different chemical reactions have different activation energies, and higher activation energies mean the reaction will proceed slower, or not at all at certain conditions.
In an industrial setting, a reaction with a high activation energy is not an attractive investment as large-scale production will be hindered by cost and time associated with a chemical reaction that has a high activation energy. A get-around to this is the use of catalysts.
Catalysts are molecules that lower the activation energy of a chemical reaction without actually participating in the chemical reaction. They do so by providing an alternative path to the reaction. Enzymes are an example of biological catalysts. For instance, in synthesis of a protein, enzymes are responsible for attaching a specific amino acid in the chain - in a way, this illustrates the function of catalysts as species that make sure orientation of reacting species are in place (and with specificity).
In the industry, catalysts would lower the cost of production, as well as the time of production, of certain chemical species, thereby making the production as efficient as possible. Examples of this include the use of iron or platinum surfaces to catalyze the production of ammonia from the reaction of hydrogen and nitrogen (above). This reaction is very inefficient and expensive without the use of catalysts.
There are other catalysts - some specific, some generally applied - used in industries - including vanadium oxide for the production of sulfuric acid, aluminosilicates for the conversion of ethene to ethanol, and zeolites for catalytic cracking of oils among others.
All these catalysts lower the activation energy of a reaction by providing an alternative route to the final product, and hence make a reaction more efficient. In the industrial setting, this will lower the time, and ultimately cost of making a product.