Chemisorption

Chemisorption

Illustration of hydrogenation on a catalyst surface, a process involving chemisorption.

Chemisorption is a type of adsorption that involves a chemical reaction between the surface and the adsorbate. This process results in a strong bond, often covalent, between the adsorbate and the surface. Chemisorption is typically characterized by its specificity, irreversibility, and the formation of a monolayer.

Mechanism

Chemisorption occurs when the adsorbate forms a chemical bond with the surface atoms of the substrate. This process can involve the sharing or transfer of electrons, leading to the formation of covalent or ionic bonds. The strength of these bonds is much greater than those involved in physisorption, which is governed by weaker van der Waals forces.

The process of chemisorption can be influenced by several factors, including the nature of the surface, the type of adsorbate, temperature, and pressure. Unlike physisorption, chemisorption is often an activated process, meaning it requires an initial input of energy to overcome an activation barrier.

Applications

Chemisorption plays a crucial role in various industrial and scientific applications. One of the most significant applications is in catalysis, where chemisorption is essential for the activation of reactants on the surface of a catalyst. For example, in the hydrogenation process, hydrogen molecules chemisorb onto the surface of a metal catalyst, facilitating the addition of hydrogen to unsaturated organic compounds.

Other applications include:

• Heterogeneous catalysis
• Surface science
• Gas sensing
• Corrosion inhibition

Characteristics

Chemisorption is characterized by the following features:

• Specificity: Chemisorption is highly specific to the type of adsorbate and the surface.
• Irreversibility: Due to the strong chemical bonds formed, chemisorption is often irreversible.
• Monolayer formation: Chemisorption typically results in the formation of a single layer of adsorbate on the surface.
• Activation energy: The process usually requires activation energy to proceed.

Related pages

• Adsorption
• Physisorption
• Catalysis
• Surface chemistry