chemiszorpió

Chemiszorpió, also known as chemisorption, is the adsorption of a chemical species onto a solid surface via the formation of chemical bonds with surface atoms. It involves electron sharing or transfer between the adsorbate and the substrate, typically requiring an activation energy. The resulting interaction is localized at specific surface sites and is usually stronger than physical adsorption.

Mechanisms include dissociative chemisorption, where a molecule dissociates upon adsorption (for example H2 into two H atoms on a metal surface), and molecular chemisorption, where the intact molecule remains bound. Bonds are typically covalent or ionic, and adsorption energies are often large (tens to hundreds of kilojoules per mole). Because chemical bonds form, chemisorption is often less reversible at moderate temperatures and pressures, though it may be reversed by heating or chemical treatment. Coverage is often sub-monolayer due to the finite density of active sites.

Compared with physisorption, chemisorption is stronger, shorter-ranged, and more site-specific. It generally features higher activation energy and slower kinetics, and can markedly alter the electronic structure of the surface and adsorbate, influencing properties such as work function and catalytic activity. Physisorption tends to be multilayer and largely reversible under moderate conditions.

Chemiszorpió is central to heterogeneous catalysis, gas sensing, corrosion protection, and surface modification. It is studied with techniques such as temperature-programmed desorption (TPD), infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning tunneling microscopy (STM), and calorimetry. Distinguishing chemisorption from physisorption relies on adsorption energies, reversibility, spectroscopic changes, and evidence of bond formation.