Brunauer-Emmet-Teller theory

During physical adsorption, each adsorbed molecule forms a new active site for the remaining gas molecules, but there is no reason why this process should limit itself to only one layer. The Brunauer-Emmet-Teller theory, which originates from the Langmuir theory, allows us to obtain a relation (BET eqiration) involving a parameter that expresses the influence of the solid s global surface area, that is to say, the area exposed to gas aetion. 

Brunauer-Emmet-Teller Theory Applied to Fractal Surfaces... 

The method as a rule used for the determination of the specific surface of a material is the Brunauer-Emmet-Teller (BET) method [2,4,5], The BET theory of multilayer adsorption for the calculation of specific surface area, S, was originally developed by Brunauer, Emmett, and Teller [2,4,5], The adsorption process, within the frame of the BET theory, is considered as a layer-by-layer process. In addition, an energetically homogeneous surface is assumed so that the adsorption field is the same in any site within the surface. Additionally, the adsorption process is considered to be immobile, that is, each molecule is adsorbed in a concrete adsorption site in the surface. Subsequently, the first layer of adsorbed molecules has an energy of interaction with the adsorption field, and a vertical interaction between molecules after the first layer,, is explicitly analogous to the liquefaction heat of the adsorbate. Besides, adsorbed molecules do not interact laterally. 

Many theories of gas adsorption have been advanced. For meso-pores the measurements are usually interpreted by using the BET theory [Brunauer, Emmet, and Teller, J. Am. Chem. Soc., 60, 309 (1938)]. Here the amount of absorbed n is plotted against the relative pressure p/po. The monolayer capacity n is calculated by the BET equation ... 

The oversimplified BET (Brunauer, Emmet and Teller) theory, valid for relative pressures between 0.05 and 0.35, allows the calculation of the specific surface area of solids and the estimation of the interactions between the solid and the vapour (from the value of the constant c). The BET equation is mainly applicable for Type II and IV isotherms. The specific surface area deduced from T)q)e I isotherms has no physical mearung because the notion of a monolayer is not applicable in the case of micropores [9,41,46,47]. 

Surface areas are usually determined by gas adsorption (nitrogen or krypton) and although there are a number of theories describing this phenomenon, the most widely used method is the Brunauer, Emmet and Teller, or BET, method. Adsorption methods for surface area determination have been reviewed in detail by Sing (1992). Two methods are used the multipoint and single-point. 

Brunauer, Emmet and Teller theory of adsorption and isotherm equation... 

Eigure 5.6 shows an isotherm obtained from nitrogen absorption measurements of TIMREX SEG44, which is a typical highly crystalhne graphite. The shape of the graphite adsorption isotherm according to the Brunauer, Emmet, and Teller theory as well as... 

The multilayer adsorption model, as shown in Fig. 2.11, was proposed by Brunauer, Emmet and Teller (BET) in 1938 to modify Langmuir s monolayer one. BET theory developed from the multilayer model can be applied to explain all types of isotherms. Based on the BET theory, a standard method for determining the specific surface area of solid catalysts was developed, which brought catalysis study into a new stage. 

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