Heterogeneous Catalysis
Definition and meaning of Heterogeneous Catalysis in chemistry.
Heterogeneous catalysis is catalysis in which the catalyst exists in a different phase, usually a solid, from the reactants, which are typically gases or liquids, with the reaction occurring at the catalyst's surface.
In more detail
The process typically follows several steps: reactant molecules diffuse to the catalyst surface, adsorb onto active sites, react while adsorbed (often after being weakened or dissociated), and the products then desorb and diffuse away. Because reaction occurs only at surface active sites, catalysts are often prepared with high surface area (porous pellets, fine powders, or supported metal particles) to maximize the number of available sites. Heterogeneous catalysts are widely used industrially because the solid catalyst can be easily separated from fluid products and often reused.
Key facts
| Field | Physical Chemistry |
|---|---|
| Catalyst phase | Typically solid |
| Reactant phase | Gas or liquid |
| Key mechanism steps | Adsorption, surface reaction, desorption |
In the Haber-Bosch process, nitrogen gas and hydrogen gas react over a solid iron catalyst (with potassium and aluminum oxide promoters) to synthesize ammonia; N2 and H2 adsorb and dissociate on the iron surface, enabling bond formation that would otherwise require far higher temperatures.
Frequently asked questions
How does heterogeneous catalysis differ from homogeneous catalysis?
In heterogeneous catalysis, the catalyst is in a different phase from the reactants (usually solid catalyst with gas or liquid reactants), and reaction occurs at the surface. In homogeneous catalysis, the catalyst is in the same phase as the reactants, typically all dissolved in solution.
Why is surface area important in heterogeneous catalysis?
Because the reaction happens only at exposed active sites on the catalyst surface, increasing surface area (via porous or finely divided materials) increases the number of active sites and thus the reaction rate.