Abstract

Hydroxy-chromium beidellite is of interest for use in catalysis and as adsorbents. The micro porosity of the materials differing in pillar density has been explored. Nitrogen adsorption data obtained at very low relative pressures were used. This paper determines the influence of the OH-Cr species on the structure and texture of modified dioctahedral smectites (beidellite). Minerals varying in cation exchange capacity pillared with various Cr pillar precursor ions can provide a family of catalysts that differ in surface area, porous structure and concentration of active sites. These data were analyzed by means of the method a_s and the BET, Langmuir and Dubinin–Radushkevich approaches. Different types of isotherm equations are used, one to describe adsorption in micro pores while another one for describing adsorption on external surfaces. All methods applied demonstrated that these solids possess micro pores over a broad pore-size range. Chromium pillared clays contain a significant amount of ultramicropores. Interlayer with larger spacing resulted in different specific surface areas and micro pore volumes. Generally, this behaviour could be related to the different structural characteristics of the smectites.

Key words: Chromium pillared clays, micro porosity analysis, nitrogen adsorption-desorption, textural study.