Assessing the pore network of hierarchical micro/mesoporous materials

F. Villemot, A. Galarneau, J. Rodriguez, F. Di Renzo, F. Fajula, B. Coasne
Institut Charles Gerhardt, FR

Keywords: hierarchical, tplot, pore network

Summary:

Microporous materials such as zeolites present remarkable potential for catalysis, adsorption, and ion-exchange due to their unique pore network. However, the nanometer size of the micropores limits mass transfer, which is required for efficient use of the active sites of the materials. To circumvent this limitation, an approach is to create a secondary pore network, with wider pores. However, the existence of a hierarchical porosity raises the question of its fine characterization using adsorption-based techniques. Among available techniques, the t-plot method is routinely applied to determine the micro- and/or the mesoporous volumes of a sample by comparison with a reference adsorption isotherm of a non-porous material having the same surface chemistry. In this presentation, we discuss the validity of the t-plot method in the case of hierarchical porous materials exhibiting both micro- and meso- porosities. We first show an intrinsic failure of the t-plot method with large errors in microporous volume determination. We further show that this error is captured using the simple thermodynamical model by Derjaguin. The effect of such a drawback on the ability of the t-plot method to estimate the micro- and mesoporous volumes of hierarchical samples is then discussed.