Application of the BET equation to experimental data

The most convenient form of the BET equation for application to experimental data is that already given in Equation (2.13), viz 

Some typical examples of BET plots are given in Figs 2.5-2.7. Those in Fig. 2.5 for nitrogen adsorption at 90K on various catalysts, taken from the 

Plot of pMp° - p) against p/p° (r is expressed in cm (stp)). (1) Unpromoted Fe catalyst (2) AljOj-promoted Fe catalyst (3) AI2O3-KjO-promoted Fe catalyst (4) fused copper catalyst (5) chromium oxide gel (6) silica gel. (Courtesy Brunauer, Emmett and Teller.) 

A number of attempts have been made to modify the BET equation so as to obtain better agreement with the experimental isotherm data in the multilayer region. One of the most recent is that of Brunauer and his co-workers  

The Type II isotherms obtained experimentally often display a rather long straight portion (BC in Fig. 2.9), a feature not strictly compatible with the properties of the BET equation which, as we have seen, yields a point of 

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A review of the application of the BET equation to experimental data the C parameter... 

Application of the BET equation to experimental data has become the standard method for surface area determinations. The constants are determined from data at low humidities (5-30% RH). Based on these parameters, the BET equation almost always overestimates the amount of water associated with the solid at high humidity. 

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