Critical Overview of Textural Characterization of Zeolites by Gas Adsorption

Abstract

Porous materials with pores within molecular size are essential to solve several technological problems taking advantage of their textural properties related to their exposed surface and porosity. Among these materials, zeolites are in the podium, with technological and industrial applications, which are directly related to pore properties (e.g., size, surface chemistry, among others). To obtain their textural properties, there are several techniques, but gas adsorption plays an important role, and it is among the most widely used for this purpose. Despite being a popular technique, with nitrogen at 77 K as the reference probe molecule to obtain adsorption isotherms, the estimation of the textural properties is not a trivial procedure. On the other hand, it is possible to perform adsorption measurements with different gases at different temperatures and pressures, whereby is crucial the choice of adequate analysis conditions because the adsorption-desorption isotherm will be the unique information obtained from the experiment. Once the data are obtained, a careful selection of methods and models to analyze them is mandatory to evaluate textural properties of the samples in a reliable and reproducible manner. Particularly for zeolites, due to their pore sizes and the presence of surface functional groups, the application of this characterization technique is not straightforward, thus needing to pay attention to the previous knowledge that exists about this type of materials, to carry out the experiment as well as to choose the appropriate methodology for data treatment. In this chapter, we introduce an overview of the experimental procedure and data treatment to obtain the more reliable textural properties for zeolites.