Adsorption and pre-adsorption for the detailed characterisation of clay catalysts

Abstract

Ion exchange and acid activation are easy and appropriate modification treatments for obtaining versatile clay derived catalysts which can be tailored for a precise reaction of interest. Depending on the specific conditions and also on the nature of the starting clays, the alterations in the porosity and the surface chemistry that occur can be determinant for the catalytic performance, in particular for selectivity. However, it is known that the detailed description of the porosity is not straightforward from the analysis by nitrogen adsorption at 77 K alone. In this work it is shown how the n-nonane pre-adsorption method, with adaptations and in combination with the alpha-S method using appropriate reference isotherm, can provide valuable information to elucidate the complex porosity of clay derived materials, with special reference to primary and secondary micropore filling. Ion exchanged clay minerals, and after acid activation, which we are currently using as catalysts, e.g. in the conversion of glycerol, will be considered. The starting clays are from the Source Clays Repository (U.S.A.) and from Porto Santo of Madeira Archipelago (Portugal).