The heterogeneous catalysts are those operating in a phase differently than the reagents or reactants in chemistry, where any substance exerts an interaction with another in a chemical reaction that leads to other substances properties, characteristics and different distribution, named products reaction or absolutely products. The vast majority of practical heterogeneous catalysts are solids but most of the reactants are gases or liquids.
In this area, different mechanisms for reactions on surfaces are known, depending on how the processes of attraction of molecules or ions of a substance are carried out on the surface of Langmuir-Hinshelwood, Eley-Rideal, and Mars-van Krevelen.
In the area of the total surface of the solid has a result that is of importance in the speed of reaction that indicates which is the smaller particle size of the catalyst, the greater is the external part of a body that serves as a limitation with the exterior for given mass of particles. For example, in the process of having the nitrogen reaction are mononuclear diatonic molecules formed by two nitrogen atoms and hydrogen are composed of two nitrogen atoms at room temperature is a flammable, colorless and odorless gas that are gaseous to produce ammonia, finely divided iron serves as a catalyst for the synthesis of ammonia which is a chemical compound whose molecule consists of anitrogen atom (N) and three hydrogen atom (H) according to the formula NH3.
The reactant gases that retain a surface between the molecules in the active sites of the iron particles, once absorbed, the bonds within the reacting molecules suffer and new bonds are integrated between the generated fragments, in part reasonable to their proximity.
