Brunauer-Deming-Teller

Figure 7.2 The Brunauer-Deming-Teller classification of isotherm types I to VI (from top left to bottom right). In each case adsorption uptake is plotted against p/Po, where p is the adsorbate pressure and Po the saturated vapour pressure of the pure liquid adsorbate at the isotherm temperature.

Fig. I.l The five types of adsorption isotherm, I to V, in the classification of Brunauer, Deming, Deming and Teller (BDDT), together with Type VI, the stepped isotherm.

Five types of isotherms for adsorption according to Brunauer, Deming, Deming, and Teller (4). 

Brunauer, Deming, Deming and Teller, based upon an extensive literature survey, found that all adsorption isotherms fit into one of the five types shown in Fig. 3.1. 

Adsorption isotherms are plots of the amount of gas adsorbed at equilibrium as a function of the partial pressure p/p°, at constant temperature. The quantity of gas adsorbed is mainly expressed as the mass of gas (usually g) or the volume of gas reduced to STP (standard temperature and pressure). The majority of isotherms which result from physical adsorption may conveniently be grouped into five classes — the five types I to V included in the classification originally proposed by Brunauer, Deming, Deming and Teller — sometimes referred to simply as the Brunauer classification [2]. The essential features of these types are indicated in Fig. 12.1. 

An extension to the BET model was put forward by Brunauer, Deming, Deming and Teller (BDDT) in 1940. The BDDT equation contains four adjustable parameters and was designed to fit the isotherm Types I-V. From a theoretical standpoint, the BDDT treatment appears to offer very little more than the original BET theory and the cumbersome equation has very rarely been applied to experimental data. 

The majority of isotherms which result from physical adsorption may conveniently be grouped into five classes, i.e., the five types I to V included in the classification originally proposed by Brunauer, Deming, Deming and Teller [4]. The essential features of these types are indicated in Fig. 13.3. 

Fig. 13.3. The six types of adsorption isotherms following the Brunauer, Deming, Deming, Teller...

B.D.D.T. = Brunauer-Deming-Deming-Teller m is the number of monolayers, and is a heat of adsorption. 

FIGURE 14.14 Adsorption data of water vapor on silica gel at 25°C. Isotherm fits Brunauer-Deming-Dem-ing-Teller Freundlich, Langmuir, and Redhch-Peterson equations. 

Brunauer, Deming, Deming, and Teller [3] later distinguished five different physical adsorption isotherms. The Type I adsorption isotherm is characteristic of chemisorption, for which the first layer is adsorbed much more strongly than subsequent layers. The type II isotherm is characteristic of the multilayer adsorption exhibited with physical adsorption near the boiling point of the adsorbate. Type III isotherms are obtained for multilayer physical adsorption with condensation of the adsorbate in narrow pores whereas Type IV isotherms are obtained when the first layer is adsorbed with a lower heat than the heat of condensation of the adsorbate. Finally, Type V isotherms are characteristic of adsorption according to Type IV on an adsorbent with narrow pores. 

The n-layer treatment mentioned above takes an account of the forces of capillary condensation. In 1940, Brunauer, Deming, Doming and Teller [132] were able to extend the BET theory by introducing an additional contribution to the energy of adsorption resulting from these forces. The so-called BDDT equation, contrary to the BET isotherm, can be applied over a wider range of relative pressures. This equation, however, is rather complex and contains four adjustable parameters which cannot be assessed independently. For this reason, this is seldom applied and only a few attempts have been made to use the equation under consideration [95,118],... 

Another important contribution by Brunauer, Deming, Deming and Teller [132] deals with the identification of five principal types of adsorption isotherms for gases and vapours. This identification is known as the BDDT classification and is recommended as the basis for a more complete classification introduced by lUPAC [15],... 

The nitrogen adsorption at 77 K of the samples is shown in Figure 1. The adsorption isotherms are of type I+II in the Brunauer, Deming, Deming and Teller (BDDT) classification... 

There are several isotherm interpretations available. The most widely used is the Brunauer, Emmett and Teller (BET) [1] and its various modifications including the Brunauer, Deming, Doming and Teller (BDDT) [2]. 

The majority of isotherms may be grouped in the six types shown in Figure 2.1. The first five types were described by Brunauer, Deming, Deming and Teller [1], Type 6 was identified later [2]. 

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