Physisorption

Physisorption or physical adsorption is a type of adsorption in which the adsorbate adheres to the surface only through Van der Waals (weak intermolecular) interactions, which are also responsible for the non-ideal behaviour of real gases. It is characterised by:
 * Low ambient temperature, always under the critical temperature of the adsorbate;
 * Type of interaction: Intermolecular forces (van der Waals forces);
 * Low enthalpy: ΔH < 20 kJ/mol;
 * Adsorption takes place in multilayers;
 * Low activation energy.
 * The energy state of adsorbate is not altered.
 * Reversible.

Examples
N2 on iron at 80 K

Notes and References
Physisorption Physisorption 物理吸着