The relation between the synthesis of pillared clays and their resulting porosity

Abstract

Clays can be converted to stable microporous materials by the incorporation of pillars. The type of pillars determine to a large extent the porosity features of the pillared clays. Different pillaring species (Al, Ti, Zr, Fe) were investigated and discussed in terms of pore volume, pore size and pore size distribution. The porosity induced by pillaring can be further modified by small modifications during the synthesis. More meso- and macroporosity can be achieved by choosing clays with smaller clay layer sizes (laponite compared to montmorillonite) or by the way of drying (air or freeze drying). Incorporation of Zr and Cr in the Fe-pillars creates mixed oxide pillared clays and pillared clays with new properties were obtained. The adsorption strength strongly increased resulting in higher adsorption capacities as demonstrated for gases (O 2, N 2 , CO 2, CO and CH 4) and chlorinated hydrocarbons. Pre-adsorption of amines effectively reduces the pillar density (Fe-PILL) and distributes the pillars more homogeneously between the layers (Al- and Ti-PILC) creating higher pore volumes and higher adsorption strength. Amines were also useful for the orientation of laponite clay layers to more regularly ordered face-to-face stacked pillared laponite clays which exhibit significant increased pore volumes.