| Popis: |
Publisher Summary The rate of adsorption would be very rapid if a clean non-porous adsorbent surface were exposed to a gas or vapor adsorbate and the fluid boundary layer adjacent to the surface offered no resistance to the transport of gas to the surface. The classical kinetic theory of gases may be invoked to assess the order of magnitude of such intrinsic adsorption rates. Physical adsorption entails attractive Van der Waals forces between adsorbate and adsorbent, and the energy barrier that molecules have to overcome for adsorption to occur is usually very small. The energy released when physical adsorption occurs is close to the heat of liquefaction of the adsorbate gas. However, for desorption to take place, a similar quantity of heat has to be absorbed. Thus, the processes of adsorption and desorption are reversible and non-activated. This is in contrast to chemisorption, in which moderately strong chemical bonds are formed and molecules need to have sufficient energy or activation energy to surmount the energy barrier and fall into the lower potential well of the chemisorbed state. |
