(227c) Mapping the Adsorption and Phase Behavior of Fluids in Micro-Mesoporous Adsorbents with Hierarchical Pore Structure:  Towards an Advanced Pore Structural Characterization

Thommes, M., Quantachrome Instruments
Cychosz, K., Quantachrome Instruments
Recently, much effort has been devoted to the development of materials which exhibit hierarchical pore structure with the appropriate balance of micropores and mesopores, as well as advantageous pore connectivity. The network of interconnected micro- and mesopores facilitates efficient transfer of fluids to and from catalytically active sites, leading to benefits in numerous catalytic applications. With the development of these materials, a large amount of work has been dedicated to their pore structural characterization. Detailed insights about the pore architecture (pore size distribution, pore volume, and pore interconnectivity) are important because they control transport phenomena, diffusional rates, and govern selectivity.

 Gas adsorption is well suited for this characterization because it assesses a wide range of pore sizes, spanning the entire micro- and mesopore range [1]. Argon (87 K) adsorption coupled with methods such as non-local density functional theory (NLDFT) allow one to obtain an accurate pore size distribution over the entire micro- and mesopore size range using a single method [1,2]. However, for an in-depth characterization of the pore network, a detailed understanding of the adsorption and phase behavior of fluids confined in such complex pore structures is needed. Within this context, we focus on a systematic experimental study of the adsorption and phase behavior of argon, nitrogen, and carbon dioxide in a series of mesoporous Y-zeolites with hierarchical pore structure and tailorable mesopore size [3] over a wide range of temperature (from below the bulk triple point to above the boiling point). An advanced interpretation of the hysteresis behavior, also as a function of temperature, allows one to obtain a detailed picture of the pore network. For this we utilized hysteresis scanning experiments, performed at various temperatures.

 Our results not only lead to a better understanding of the fundamental aspects of the adsorption and phase behavior of fluids in such hierarchically structured micro-mesopore networks, but also contribute to the development of new methodologies for an accurate and detailed pore structural characterization, which is crucial for advancing the application of nanoporous materials such as mesoporous zeolites in catalysis, separations, and other industrial processes.

[1] Thommes, M., Cychosz, K.A. Adsorption 20, 233 (2014).

[2] Landers, J., Gor, G.Y., Neimark, A.V. Colloids Surfaces A 437, 3 (2013).

[3] Garcia-Martinez, J., Xiao, C., Cychosz, K.A., Li, K., Wan, W., Zou, X., Thommes, M. ChemCatChem 6, 3110 (2014).