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Chemical adsorption occurs due to the uneven force field present on the solid surface; the atoms on this surface often still possess residual bonding capacity. When gas molecules collide with the solid surface, electron exchange, transfer, or sharing takes place between them and the surface atoms, resulting in the formation of adsorption bonds through this adsorption process. Adsorption characteristics: Compared with physical adsorption, chemical adsorption has the following main characteristics: ① The forces involved in adsorption are comparable to chemical bond forces, and are much stronger than van der Waals forces. ②The adsorption heat is approximately equal to the reaction heat. ③The adsorption is monolayered. Therefore, it can be described by the Langmuir isotherm, and sometimes by the Freundlich equation as well. Temkin’s adsorption isotherm applies only to chemical adsorption: in the equation, V is the adsorption volume at an equilibrium pressure of p ； Vm is the single-layer saturated adsorption volume ； a and c0 are constants. ④Selective. ⑤It is irreversible with respect to temperature and pressure. Furthermore, chemical adsorption often also requires an activation energy. To determine whether an adsorption is chemical adsorption, it is mainly based on the adsorption heat and irreversibility. The adsorption mechanism can be divided into 3 cases: ① Gas molecules lose electrons and become positive ions, while the solid gains electrons; as a result, the positive ions are adsorbed on the negatively charged solid surface. ②The solid loses electrons while gas molecules gain electrons, resulting in negative ions being adsorbed on the positively charged solid surface. ③Gases and solids share electrons to form covalent bonds or coordinate bonds. For example, the adsorption of gases on metal surfaces often occurs because the electrons of the gas molecules form covalent bonds with the d-electrons of the metal atoms, or the gas molecules provide a pair of electrons to form coordinate bonds with the metal atoms. Its role and research in heterogeneous catalysis: In heterogeneous catalysis, most cases involve the catalysis of gas-phase reactions on solid surfaces, and this is closely related to adsorption on those solid surfaces. In such catalytic reactions, at least one of the reactants is chemically adsorbed on the solid surface, and this adsorption is a key step in the catalytic process. In the adsorption layer on a solid surface, the density of gas molecules is much higher than in the gas phase. However, catalysts accelerate reactions not primarily as a result of an increased surface concentration, but mainly because the adsorbed molecules, ions, or groups possess high reactivity. When gas molecules are chemically adsorbed on a solid surface, they may undergo dissociation, deformation, etc., which can **increase their reactivity. Therefore, the study of chemical adsorption is very important for elucidating catalytic mechanisms. Chemical adsorption is related to the structure of the solid surface. There are many new methods and techniques in the study of chemical adsorption on surface structures, such as field emission microscopy, field ion microscopy, low-energy electron diffraction, infrared spectroscopy, nuclear magnetic resonance, chemical analysis by electron energy spectroscopy, isotope exchange method, and others. Among them, field emission microscopy and field ion microscopy can directly observe adsorption on different crystal planes as well as the positions of individual atoms on the surface, thus providing the most direct evidence for the study of lattice defects, adsorption properties, and mechanisms of various surfaces.