8.2 Physical and chemical adsorption
Furthermore, the adsorbed atoms are localized at particular sites on the solid surface and only one layer of adsorbate may be chemisorbed. 化学吸附的位点是特定的，吸附的层数只能为一。
ΔG= Δ H-T Δ S
8.1 Introduction 引言
The adsorption of gases plays an important role in many processer, in particular heterogeneous catalysis（异相催化）. 气体的吸附在很多进程中其重要作用，尤其是异相催化。
8.2 Physical and chemical adsorption
In chemisorption, on the other hand, a chemical bond is formed. Consequently the enthalpies of the adsorption are much greater (~>80kJ/mol) than for physical adsorption. There are occasional exceptions (e.g. for the chemisorption of hydrogen on glass the enthalpy is only about 12 kJ/mol). 化学吸附存在化学键的形成， 其焓变大得多(~>80kJ/mol) 。 不过也有例外。
“The calculations for the supported system clarify that the γ-Al2O3 support increases NO activation for three-fold sites, while it decreases it for on-top and bridge sites.”
8.1 Introduction 引言
It is the weakening or breaking of chemical bonds that occurs upon adsorption that makes some solid surfaces effective catalysts（催化剂） for gas phase reaction. 吸附的同时发生化学键的减弱或者加强，导致某些固体成为 气相反应的催化剂。
8.2 Physical and chemical adsorption Comparing physical and chemical adsorption
Specificity 特异性 As chemical adsorption involves a chemical between gas molecules and groups on the surface of the solid it is highly specific. Physical adsorption, on the other hand， and occurs with any gas-solid combination under the appropriate conditions of temperature and pressure. 化学吸附因为存在化学反应而有特异性，但物理吸附则 只要有合适的温度和压强即可发生。
NO在P4上的三种化学吸附的形式
Fig. 4 Calculation models of NO adsorption on Pt 4 /γ-Al 2 O 3 : (a) on-top site, (b) bridge site, and (c) three-fold site. Ryota Ishimoto , Changho Jung , Hideyuki Tsuboi , Michihisa Koyama , Akira Endou , Momoji Kubo , Carlos A. Del Ca... Periodic density functional and tight-binding quantum chemical molecular dynamics study of catalytic properties on γ Al2O3 supported Pt catalysts Applied Catalysis A: General, Volume 305, Issue 1, 2006, 64 - 69 /10.1016/j.apcata.2006.02.049
8.2 Physical and chemical adsorption
The adsorption of a gas (often called the adsorbate吸附质 ) on a solid surface (often called the adsorbent吸附剂) may involve only physical interactions due to van der Waals force, or there may be a chemical interaction between the solid and the gas. 吸附质和吸附剂之间可能存在范德华力的物理相互作用 ，或者化学相互作用。
8.2 Physical and chemical adsorption Comparing physical and chemical adsorption
In comparing the characteristic of physical and chemical adsorption it is useful to use the analogies with condensation and chemical reaction. It will be seen that no single characteristic can be used to distinguish these two types of adsorption as there are often exceptions, so several characteristics should be examined.
Activated carbon is used as an adsorbent
8.2 Physical and chemical adsorption
Physical adsorption, because involves only the forces of molecular interaction, is very similar to the condensation of a vapor to form a liquid. 物理吸附只涉及分子间力，所以和气体的凝聚类似。
第五章——气固界面
李硕琦 山东科技大学材料学院 2015.4
ቤተ መጻሕፍቲ ባይዱ
8 The gas-solid interfaces: adsorption; catalysis
8.1 Introduction 引言
A solid surface in contact with gas usually attracts an adsorbed layer of gas molecules. When adsorption occurs the process is spontaneous, which means the free energy change, ΔG, is negative. In most cases there is also a decrease in entropy(熵), ΔS, because the gas loses degrees of freedom. Hence, to ensue that ΔG is negative, the enthalpy(焓)，ΔH，negative and large enough to outweigh the entropy term: 固体表面和气体接触时会吸附一层 气体分子，如果该过程是自发的， 即意味着ΔG是负的。 而此时ΔS 下降，所以， ΔH一定为负， 而且超过ΔS项。
Fig. 3 Optimized structure of Pt 4 /γ-Al 2 O 3 system: (a) side view; (b) top view.
氧化铝表面的P4催化剂
Ryota Ishimoto , Changho Jung , Hideyuki Tsuboi , Michihisa Koyama , Akira Endou , Momoji Kubo , Carlos A. Del Ca... Periodic density functional and tight-binding quantum chemical molecular dynamics study of catalytic properties on γ Al2O3 supported Pt catalysts Applied Catalysis A: General, Volume 305, Issue 1, 2006, 64 - 69 /10.1016/j.apcata.2006.02.049
8.2 Physical and chemical adsorption
The enthalpy (焓变) of the physical adsorption is roughly (20 kJ/mol) the same as the enthalpy of condensation and in many ways the adsorbed materials, especially when many layers have been adsorbed, behaves like a two dimensional liquid. 物理吸附的焓变大约是20 kJ/mol，和凝聚的焓变相同。