Crystal-fluids interaction in zeolites at high pressure

Zeolites (natural or synthetic) are a class of open-framework silicates with cavities, in the form of channels or cages, with diameters shorter than 2 nm. These porous materials respond to the applied pressure differently, in response to the nature of the pressure-transmitting fluids, used to compress hydrostatically the materials under investigation. For instance, cavities can be accessed or filled by suitable guest chemicals, intruded in the zeolitic pores upon compression. Moreover, pressure can play an important role also in increasing the efficiency of zeolites as "nano-reactors", favoring the access of reactants and products to/from the catalytically active sites and the aggregation of molecules in the cavities. Over the last years [1,2,3], we have performed a series of experiments - by in-situ single-crystal and powder synchrotron diffraction using a number of penetrating and non-penetrating pressure transmitting fluids with a diamond anvil cell – in order to describe the crystal-fluid interaction upon pressure of a series of natural or synthetic zeolites with different topologies and compositions, expected to favor or not the penetration of liophilic/hydrophobic guest species. The following aspects were investigated: 1) the structural deformations of the tetrahedral framework in response to the isotropic compression regime; 2) the unit-cell variations with pressure and the elastic anisotropy; 3) the penetration of molecules of the P-fluid (e.g., H2O, methanol, ethanol, ethylene glycol), along with the host-guest and guest-guest interactions; 4) the reversibility extents of the observed phenomena. The authors acknowledge the Italian Ministry of Education, MIUR-Project: “Futuro in Ricerca 2012 - ImPACT- RBFR12CLQD”.