Pressure-mediated crystal-fluid interaction in the zeolite offretite

The high-pressure behaviour and the crystal-fluid interaction of a natural offretite have been investigated by in situ single-crystal synchrotron X-ray diffraction, using a diamond anvil cell. Five different P-transmitting fluids have been employed: the non penetrating daphne oil 7575 and the potentially penetrating methanol:ethanol:H2O = 16:3:1 mixture, ethanol:water = 1:1 mixture, distilled H2O and liquid Ne. The daphne oil 7575 experiment allowed to describe the intrinsic compressional behavior of offretite, without any pressure-induced crystal-fluid interaction, with an isothermal bulk modulus KV0 = 59(2) GPa (βV0 = 0.0170(9) GPa-1) for the range Pamb-1.83(5) GPa. All the experiments in potentially penetrating P-transmitting fluids showed the P-induced sorption of extra molecules within the large 12mRs channel of offretite, obtained on the basis of X-ray structure refinements. For the aqueous mixtures, the magnitude of the adsorption appears to be governed by the H2O content of the P-transmitting fluid. Ne atoms are also able to penetrate into the 12mR channel in response to the applied pressure, interacting with the extraframework population via weak Van der Waals attraction. A comparative analysis of the P-mediated crystal-fluid interaction phenomena between offretite and the structurally similar erionite is provided.