First, the nature is different.
1, physical adsorption
Physical adsorption, also known as van der Waals adsorption, is caused by intermolecular force between adsorbate and adsorbent, also known as van der Waals force.
2. Chemical adsorption
Chemical adsorption refers to the transfer and exchange of adsorbate molecules with atoms (or molecules) on the solid surface or the adsorption of electrons to form adsorption chemical bonds.
Second, the main features are different.
1, physical adsorption
① The physical adsorption of gas is similar to the liquefaction of gas and the condensation of steam, so the heat of physical adsorption is small, which is similar to the liquefaction heat of corresponding gas.
② The higher the boiling point of gas or steam or the lower the saturated vapor pressure, the easier it is for them to liquefy or condense, and the greater their physical adsorption capacity.
③ Physical adsorption generally does not require activation energy, so the adsorption and desorption rates are relatively fast. As long as the temperature is appropriate, any gas can be physically adsorbed on any solid without selectivity.
④ Physical adsorption can be monolayer adsorption or multi-molecular adsorption; ⑤ The adsorbed molecular structure has not changed much, and no new chemical bonds have been formed, so there are no new absorption peaks in infrared and ultraviolet spectra, but there may be shifts.
⑤ Physical adsorption is reversible.
2. Chemical adsorption
(1), the force involved in adsorption is equivalent to chemical bond force, which is much stronger than 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's isothermal formula, and sometimes it can also be described by freund's rich formula.
4. selectivity.
⑤ Irreversibility to temperature and pressure.
Third, the application is different.
1, physical adsorption
Physical adsorption is widely used in chemical industry, petroleum processing industry, agriculture, pharmaceutical industry, environmental protection and other departments and fields. The most commonly used is to recover useful substances or remove impurities from gas and liquid media, such as gas separation, gas or liquid drying, oil decoloration and so on.
2. Chemical adsorption
Pulse chemisorption, catalyst pretreatment, isothermal reaction, BET specific surface area. Used to characterize catalysts, such as metal dispersion, active metal surface area, number of acid centers and strength distribution.
Baidu encyclopedia-physical adsorption
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