A catalyst is a substance that can modify the rate of a chemical reaction without being consumed itself in the process. Catalysts may be gases, liquids or solids and they may function in single phase (i.e. gas or liquid only) or multi-phase (e.g. gas-solid) systems.
Catalysts are vital to the chemical industry and are now used in most industrial chemical processes. Process benefits derive from cost savings (via improved chemical and energy efficiencies) and from reducing the environmental impact of chemical operations.