A catalyst is any substance that speeds up a chemical reaction, or lowers the temperature or pressure needed to start one, without itself undergoing any permanent chemical change.
Catalysis is the process of adding a catalyst to facilitate a reaction. A catalytic reaction is any process that involves use of a catalyst. Enzymes are naturally occurring catalysts that are responsible for many essential biochemical processes.
Increasingly specialized catalysts have been developed during the past few decades, some of which have had beneficial effects on protecting the environment and on public health. For example, they have resulted in the development of more efficient techniques for producing biofuels and hydrogen and for converting carbon dioxide into fuels and various chemicals. They are also making possible the production of plastics with increased biodegradability, of less harmful fertilizers, and of improved pharmaceuticals.