chemisorb

Chemisorption, or chemical adsorption, refers to the process by which an adsorbate forms a chemical bond with a solid surface. The verb form is chemisorb, and the noun form is chemisorption (also spelled chemosorption). The bond can be covalent, ionic, or metallic in character, and it typically involves electron transfer or sharing between the adsorbate and surface atoms. Because of the electronic rearrangement involved, chemisorption is usually highly specific for the adsorbate–surface pair and often associated with activation of the adsorbate or the surface.

Its energetics are substantially larger than those of physisorption, with enthalpies of adsorption ranging from tens to hundreds or even thousands of kilojoules per mole, depending on the system. As a result, chemisorption is typically slower to form and can be less reversible than physical adsorption, though reversibility depends on temperature and pressure. Chemisorbed species may remain intact on the surface, or dissociate the molecule upon adsorption (dissociative chemisorption).

Chemisorption is contrasted with physisorption, which involves weak van der Waals forces, is generally non-specific, occurs at lower temperatures, and is easily reversible. The coverage and rate of chemisorption are strongly influenced by surface structure, availability of active sites, temperature, and gas composition. Kinetic models such as the Langmuir isotherm are often used, with the caveat that real surfaces may deviate from ideal assumptions.

Applications and relevance: in heterogeneous catalysis, many reactions proceed via chemisorption of reactants on metal or oxide surfaces, activating bonds for subsequent transformation. It also underpins gas sensing, corrosion processes, and hydrogen storage materials. Experimental evidence comes from techniques such as temperature-programmed desorption, X-ray photoelectron spectroscopy, infrared spectroscopy, and scanning tunneling microscopy.