Spring or bumper/shock absorber: how different electrolyte aqueous solutions, intruded at HP, change the Si-chabazite energetic behavior

Hydrophobic porous materials, as pure-silica zeolites, can be used for energy storage by means of highpressure (HP) intrusion of a non-wetting fluid (Tzanis et al., 2012). After pressure release, the system can display different behaviors as spring, shock-absorber or bumper, depending on structural parameters (i.e. pore size) and the nature of the intruded liquid (Arletti et al., 2016). For example, with water or 10M LiCl aqueous solution as non-wetting liquid, the “*BEA-type zeosil-liquid” system, shows a bumper behaviour, whereas, increasing the concentration of the solution (15-20M LiCl), a shock-absorber behaviour is observed (Ryzhikov et al.,2014). These results suggest that analogous modifications can occur in similar systems and the interactions among intruded species and host material drive the behaviour of the systems. The case of pure Si-chabazite (Si-CHA) is here presented, and the intrusion/extrusion behaviours of 3 electrolytic aqueous solutions (NaCl, NaBr and CaCl2) are compared. Structural investigations during intrusion/extrusion cycles were performed by in situ X-ray powder diffraction to unravel the nature of the intruded species and their interactions with the zeolitic framework. During compression, the 3 systems display similar trends as far as cell parameters evolution is concerned. Specifically, penetration of comparable extra-framework volumes occurred at similar P values. Independently on the nature of the penetrating media, the following main steps were recognized: i) water intrusion; ii) water and ions intrusion (~0.26 GPa); iii) reaching of the maximum penetration of the extra-framework species. Upon P release, the 3 systems present different behaviors. Si-CHA intruded by NaCl and NaBr aqueous solutions does not recover the initial cell volume and retains the intruded extra-framework species. On the contrary, CHA intruded by CaCl2 completely recovers the initial cell parameters and both ions and water molecules are released. This data has been structurally interpreted on the basis of the electrolyte/ zeolite interactions. Interestingly, the extrusion behavior results to be mainly determined by the interactions of the anion with CHA silanol defects. Arletti, R., Ronchi, L., Quartieri, S., Vezzalini, G., Ryzhikov, A., Nouali, H., Daou, T.J & Patarin, J. (2016): Intrusionextrusion experiments of MgCl2 aqueous solution in pure silica ferrierite: Evidence of the nature of intruded liquid by in situ high pressure synchrotron X-ray powder diffraction. Microporous Mesoporous Mater. 235, 253-560. Ryzhikov, A., Khay, I., Nouali, H., Daou, T.J. & Patarin, J. (2014): A drastic influence of the anion nature and concentration on high pressure intrusion-extrusion of electrolyte solutions in Silicalite-1 Phys. Chem. Chem. Phys., 16, 17893. Tzanis, L., Trzpit, M., Soulard, M. & Patarin, J. (2012): Energetic Performances of Channel and Cage-Type Zeosils. J. Phys. Chem., 116(38), 20389-20395.