Scientific Results

Insertion and Confinement of H2O in Hydrophobic Siliceous Zeolites at High Pressure

Year: 2019

Authors: Santoro M., Veremeienko V., Polisi M., Fantini R., Alabarse F., Arletti R., Quatieri S., Svitlyk V., van der Lee A., Rouquette J., Alonso B., Di Renzo F., Coasne B., Haines J.

Autors Affiliation: CNR INO, Ist Nazl Ott, I-50019 Sesto Fiorentino, Italy; European Lab Non Linear Spect LENS, I-50019 Sesto Fiorentino, Italy; Univ Montpellier, CNRS, ENSCM, ICGM, F-34095 Montpellier 5, France; Univ Modena, Dipartimento Sci Chim & Geol, I-41125 Modena, Italy; Elettra Sincrotrone Trieste, I-34149 Trieste, Italy; Univ Torino, Dipartimento Sci Terra, I-10125 Turin, Italy; Univ Messina, Dipartimento Sci Matemat & Informat Sci Fis & Sci, I-98166 Messina, Italy; ESRF, F-38000 Grenoble, France; Univ Montpellier, CNRS, IEM, F-34095 Montpellier 5, France; Univ Grenoble Alpes, CNRS, LIPhy, F-38058 Grenoble, France

Abstract: The insertion of H2O in the siliceous zeolites TON (Theta-one) and MFI (Mobil Five) was studied at pressures up to 0.9 GPa by synchrotron X-ray diffraction, infrared spectroscopy, and Monte Carlo modeling. TON (orthorhombic, Cmc2(1)) and MFI (monoclinic, P2(1)/n) have 1D and 3D pore systems, respectively. H2O insertion was quantified by a combination of structure refinements and Monte Carlo modeling. Complete pore filling is observed at 0.9 GPa in the high-pressure forms of TON (orthorhombic, Pbn2(1)) and MFI (orthorhombic, Pnma). This corresponds to more than twice as many H2O molecules per SiO2 unit in the 3D pore system of MFI than in the 1D pore system of TON. This results in a greater swelling of the MFI system as compared to the TON system upon insertion. In both cases, both experiments and modeling indicate that the density of water in the pores is close to that of bulk water at the same pressure. A greater degree of molecular disorder is observed in the 3D H2O network of MFI. Infrared spectroscopy indicates a weakening of the hydrogen bonds associated with geometrical constraints because of confinement. The majority of the H2O molecules are extruded on pressure release, indicating that this insertion is reversible to a great extent, which gives rise to the molecular spring properties of these materials.

Journal/Review: JOURNAL OF PHYSICAL CHEMISTRY C

Volume: 123 (28)      Pages from: 17432  to: 17439

KeyWords: siliceous zeolites
DOI: 10.1021/acs.jpcc.9b04860

Citations: 1
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