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How is homogeneous catalysis different from heterogeneous catalysis?
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catalysis
Nanoparticles of a gold-palladium (yellow-blue) alloy supported on acid-treated carbon (gray) directly catalyzing hydrogen peroxide formation from hydrogen (white) and oxygen (red) while shutting off unwanted hydrogen peroxide decomposition.
The primary difference between homogeneous and heterogeneous catalysis lies in the physical state of the catalyst relative to the reactants.1
- Homogeneous Catalysis: The catalyst is molecularly dispersed within the same phase as the reactants, typically as a gas or a liquid. Because they exist in the same state, the catalyst and reactants are uniformly mixed throughout the reaction medium.12
- Heterogeneous Catalysis: The catalyst and the reactants exist in different phases, separated by a distinct phase boundary. Most commonly, the catalyst is a solid, while the reactants are gases or liquids that undergo chemical change at the catalyst's surface.13
While both types of catalysis function by lowering the activation energy of a reaction without being consumed, they are distinguished by this fundamental difference in physical distribution. Heterogeneous reactions are of significant practical interest in industrial processes, though they are often more complex to study than single-phase homogeneous reactions due to the interface interactions involved.143