What is a catalyst, and how are they used in the chemical industry?

The action of catalyst is shown in the diagram. It does not (and cannot) affect the thermodynamics of the reaction (both catalyzed and uncatalyzed reaction have the same energy change). However, here the activation energy of the reaction has been reduced by the catalyst, so that more reactant molecules have the required activation energy to undergo reaction. The rate of the reaction will thus increase.

Catalysts are extensively used in industry to enable chemical transformations. Generally, the catalyst is embedded on a surface, and the reactant molecules are pumped over the surface (this would be an example of heterogeneous catalysis because the catalyst and the product/reactants are in different phases - precious metal surfaces are very commonly employed). Sometimes, the catalyst is in the same phase as the reactants. These so-called homogeneous catalysts are so active that there may be loaded at such low concentrations that there is no need to recover them from the product.

Heterogenenous catalysts are very common industrially, and catalyze such processes as methanol and ammonia production. Polymer formation is also extensively catalyzed.

Catalysts are common substances found in chemistry and biology. Many substances can be a catalyst. A catalyst is a chemical or compound that lowers the activation energy of a reaction.

All reactions that take place require a certain amount of energy to "activate" or start. In the human body many reactions wouldn't be feasible without a catalyst (in the form of enzymes) because the energy requirements would be to great for the body to initiate.

Many factors can influence when a reaction takes place such as temperature of the reaction vessel. However a catalyst is the easiest way to initiate a reaction at a feasible temperature and energy level.

Its also extremely important to note that a catalyst cannot be used up once the reaction is finished. The catalyst can interact with the compounds in the reaction but once the reaction is finished the catalyst must still be present in its entirety or else it would change the products of the reaction.

To explain further, a catalyst cannot change the energy required to react, however it can provide another "path" to the same products which requires less energy.

A catalyst can also just provide an inert surface on which to react -for example iron in the reaction to create Ammonia.

credit to anor277 for clarifying something I glossed over