The microporosity of chromia-and titania-pillared clays differing in pillar density has been explored. Nitrogen adsorption data determined at very low relative pressures were used. These data were analyzed by means of the a s method and the BET, Langmuir, Dubinin-Radushkevich and Dubinin-Stoeckli approaches. The applicability of these methods for determination of the PILCs' microporosity was studied. The surface area calculated by the a s method can be considered as a total surface area of the materials studied. The BET method underestimates, whereas the Langmuir approach overestimates, the total surface area of these solids. The Dubinin-Radushkevich method can be applied only to characterize textural features of PILCs exhibiting homogeneously distributed narrow micropores (<0.7-1.0 nm width). The same holds for the Dubinin-Stoeckli relation. The method developed by Zhu et al. is useful for the determination of the porous structure of PILCs having a significant contribution of supermicropores (0.7-2.0 nm width). A good agreement between the total micropore volume of the materials studied and that obtained from the a s method was found. All the methods applied demonstrated that these solids possess micropores over a broad pore-size range.
Chromia-pillared montmorillonites contain a significant amount of ultramicropores (<0.7 nm width), whereas titania-pillared clays show an important contribution of supermicropores. An alteration of the pillar density can provide a family of pillared clays that differ in the surface area, micropore volume, and micropore size distribution.