IUPAC classification, adsorption isotherms

Given the complexity of the pore structure in high-surface-area catalysts, six types of adsorption isotherms have been identified according to a classification advanced by IUPAC 145-481. Out of these six, only four are usually found in catalysis ... 

Figure 4.30 Adsorption isotherms according to IUPAC classification.

Figure 9.13 Basic types of adsorption isotherms by IUPAC classification [53],...

The nitrogen adsorption/desorption isotherms show typical type IV profiles (IUPAC classification [18]) for the pristine MCM-48 and the Co/Fe/O/MCM-48 silica materials A and B (figure 3). 

IUPAC) classification of the adsorption isotherms79 in Figure 2. The sixth isotherm in Figure 2 is recently added. 

Bilayer architectures formed in M2(2)3(N03)4 n (where M = Co, Ni and Zn) were one of the first systems of coordination polymers to be shown as porous materials [43]. The bilayer architectures interdigitate with each other leaving small channels in the crystal lattice which were occupied by solvated water molecules. Powder X-ray studies indicate that the water molecules can be removed from the network without causing any distortion or decomposition of the network. The adsorption studies of water removed and dried sample indicated that the material is capable of adsorbing CH4, N2 and 02. About 2.3 mmol of CH4 and 0.80 mmol of N2 or 02 are adsorbed per gram of anhydrous material. The adsorption-readsorption followed the same isotherm, indicating the stability of the network throughout the process. Further, the isotherms for the adsorption-readsorption can be classified as type I in the IUPAC classification [48]. 

Adsorption/separation processes are based on adsorption isotherms (thermodynamics) and intracrystalline diffusivity (kinetics). Figure 16.1 illustrates various shapes of adsorption isotherms depending on the VOC nature, trichloroethylene (TCE) and tetrachloroethylene (PCE), and of the zeolite, MFI with Si/Al > 500 and FAU (Si/Al > 100) (14). The isotherms of VOCs adsorbed on FAU present a more or less S-shape which corresponds to type V of the IUPAC classification. In contrast, the isotherms of VOCs on MFI are more of type I, with the additional particularity of a step at 4 molecules per u.c. for PCE adsorption. The... 

Experimental adsorption isotherms recorded in the literature, measured on a wide variety of gas-solid systems, have a wide variety of forms. Nevertheless, the majority of these isotherms which result from physical adsorption may conveniently be grouped into six classes in the IUPAC classification (cf. Figure 1.7). The first five types (I to V) of the classification were originally proposed by S. Brunauer, L.S. Deming, W.S. Denting and E. Teller as the BDDT classification (1940), sometimes referred to as the Brunauer classification (1945). 

In the original IUPAC classification, the hysteresis loop was said to be a characteristic feature of a Type IV isotherm. It is now evident that this statement must be revised. Moreover, we can distinguish between two characteristic types of hysteresis loops. In the first case (a Type HI loop), the loop is relatively narrow, the adsorption and desorption branches being almost vertical and nearly parallel in the second case (a Type H2 loop), the loop is broad, the desorption branch being much steeper than the adsorption branch. These isotherms are illustrated in Figure 13.1 as Type IVa and Type IVb, respectively. Generally, the location of the adsorption branch of a Type IVa isotherm is governed by delayed condensation, whereas the steep desorption branch of a Type IVb isotherm is dependent on network-percolation effects. 

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