Intrusion-extrusion 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 / Arletti, Rossella; Ronchi, Laura; Quartieri, Simona; Vezzalini, Giovanna; Ryzhikov, Andrey; Nouali, Habiba; Daou, T. Jean; Patarin, Joël.
ABSTRACTExperimental intrusion-extrusion isotherms of MgCl 2 21H 2 O solution were recorded at room temperature on pure silica FER-type zeolite (Si-FER). The intrusion occurs at 195 MPa and the phenomenon is completely reversible with a slight hysteresis. The "Si-FER -MgCl 2 aqueous solution" system behaves like a spring. The material was deeply characterized before and after intrusion-extrusion experiments and no significant changes were observed. The unit cell parameters were refined -on the basis of the in situ synchrotron X-ray powder diffraction data -up to 1.47 GPa and then at P amb upon pressure release. The Rietveld refinement of the data collected at 0.28 GPa (280 MPa), a pressure close to the intrusion value, shows that both ions and water molecules present in the MgCl 2 aqueous solution were intruded in the porosities. However, the solvation degree of the intruded ions differs from the initial solution, revealing a partial desolvation of both magnesium and chloride ions. As a whole, the nature and amount of the intruded species correspond to a MgCl 2 10H 2 O composition. Moreover, at a higher pressure (0.68 GPa), a phase transition from the orthorhombic Pmnn to the monoclinic P2 1 /n s.g. is observed in Si-FER. At 1.47 GPa, the zeolite maintains this monoclinic symmetry, while another phase transition, to the monoclinic P2 1 s.g., is argued from the analysis of the pattern of the sample compressed to 2.6 GPa and then collected upon pressure release to ambient conditions.
KEYWORDS.FER-type zeolite, pure silica ferrierite, intrusion-extrusion experiments, in-situ high pressure synchrotron XRPD experiments, structural refinement.