The main characteristics of chemical adsorption are: only monolayer adsorption occurs; the adsorption heat is equivalent to the chemical reaction heat; selective; mostly irreversible adsorption; the adsorption layer can remain stable at higher temperatures. Chemisorption can be divided into activated adsorption that requires activated energy and non-activated adsorption that does not require activation energy. The former has a slower adsorption rate and the latter has a faster adsorption rate.
Chemisorption is an important step in heterogeneous catalytic reactions. The study of chemical adsorption is of great significance to understand the mechanism of heterogeneous catalytic reactions and to realize the industrialization of catalytic reactions. Compared with physical adsorption, chemical adsorption has the following characteristics: ① The force involved in adsorption is equivalent to the chemical bonding force, which is much stronger than the van der Waals force. ② The heat of adsorption is approximately equal to the heat of reaction. ③ Adsorption is monolayer. So it can be described by Langmuir isotherm, and sometimes by Freundlich's formula. ④ Selective. ⑤Irreversible to temperature and pressure. In addition, chemisorption often requires activation energy. The determination of whether an adsorption is chemisorption is based primarily on the heat of adsorption and irreversibility.