Characterization of the microporosity of chromia- and titania-pillared montmorillonites differing in pillar density. I. Adsorption of nitrogen

The microporosity of chromia- and titania-pillared clays differing in pilla r density has been explored. Nitrogen adsorption data determined at very lo w relative pressures were used. These data were analyzed by means of the al pha(s) method and the BET, Langmuir, Dubinin-Radushkevich and Dubinin-Stoec kli approaches. The applicability of these methods for determination of the PILCs' microporosity was studied. The surface area calculated by the alpha (s) method can be considered as a total surface area of the materials studi ed. The BET method underestimates, whereas the Langmuir approach overestima tes, the total surface area of these solids. The Dubinin-Radushkevich metho d 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 agr eement between the total micropore volume of the materials studied and that obtained from the alpha(s) method was found. All the methods applied demon strated that these solids possess micropores over a broad pore-size range. Chromia-pillared montmorillonites contain a significant amount of ultramicr opores (<0.7 nm width), whereas titania-pillared clays show an important co ntribution of supermicropores. An alteration of the pilar density can provi de a family of pillared clays that differ in the surface area, micropore vo lume, and micropore size distribution. (C) 2000 Elsevier Science B.V. All r ights reserved.