Examples of Two Plane Adsorption

An example of a multiplane adsorption has already been presented in Fig. 75. This, however, is a compilation of isotherms for carbon adsorbent. Examining just one isotherm for carbon, for example N2 adsorption on Sterling FT carbon in Fig. 83, the break in the isotherm is stiU obvious, if not more so. In this figure, there are two lines drawn on the right axis corresponding to a monolayer of the total surface, the upper line, and a mono-layer of the high-energy planes only, the lower line. It seems unlikely that 

Another example of multiplane adsorption is the 1000°C fired thoria powder mentioned in Chapter 3. This sample, however, evidences some mesoporosity and will be a good example to analyze in the next chapter. 

The comparison to isotherms, when there is a distribution, comes back to the Henry s law question. Why is it that sometimes one observes the Freundlich isotherm and thus at least the appearance that the pressure and adsorbate amount simultaneously approach zero. As demonstrated in Ch ter 4 a log-normal distribution in yields the Dubinin-Polanyi (DP) set of isotherms of which the Freundlich isotherm is a subset. The Toth isotherm is similar but mathematically not in this class. The question becomes, are the generated isotherms, and not just the energy distributions, similar. 

For these isotherms, especially the DP and Toth isotherms, not only must the distribution in be considered but also the distribution in the micropore sizes. The reason for this is that these two distributions are close enough to overlap somewhat, thus interacting to change the values of the parameters. 

As a review, the general form for the Freudlich-Dubinin-Polanyi equation is 

---