Introduction
Many chemical reactions don't happen unless they are in the presence of a third substance called a catalyst. Although the catalyst does not enter the reaction and does not change itself, it has a key effect in the start and continuation of the actual chemical process. 

Catalysis plays a key part in all our lives and is of vital importance to our present-day standard of living and quality of life because of the many products and energy related activities derived from its application.  Catalysts represent a major material industry. The 1989 U.S. catalyst market was $1.9 billion [$5 billion, worldwide]. In 1999, the catalyst market is approaching $3 billion in sales.