Physisorption of Gases by Solids: Fundamentals, Theories and Methods for the Textural Characterisation of Catalysts

Abstract

The knowledge of textural parameters, such as surface area, pore volume and pore width, usually contributes to the understanding of the behaviour of a catalyst in a process, since the extent of surface can be determinant for an efficient distribution of catalytically active sites, while the type of porosity can affect the accessibility and the diffusion process of reactant and product molecules through the porous structure. Gas adsorption is a powerful mean for the textural characterisation of powders and nanoporous solids. Despite the fact that recent developments for the characterisation of porous solids have been dedicated to advanced computational methods for modelling adsorption in nanoporous materials, it is unquestionable that the classical methods of adsorption data analysis are those available for the majority of researchers needing to characterise their materials in everyday work and can still provide, in most cases, the necessary information. However, it is obvious that the methods have to be carefully selected and properly applied, for the particular system under study, otherwise the parameters may be significantly inaccurate or even meaningless. Therefore, some classical methods to obtain surface area and pore volume are addressed and their advantages and limitations are critically evaluated on the basis of the type of mechanism of adsorption involved. A brief overview of some procedures for the determination of pore size and pore size distributions is also considered.