Inelastic Neutron Scattering Studies of Water in Natural Zeolites

Abstract

Diffusion / Neutron Scattering / Transport PropertiesResults on the motion of water molecules in six natural zeolites (natrolite, phillipsite, harmotome, heulandite, stilbite and chabazite) from incoherent inelastic neutron scattering are presented. The spectra for five zeolite samples exhibit broad maxima and few resolved peaks. Only for natrolite with water molecules tightly bound to the alumosilicate framework a spectrum with well-resolved peaks is observed. A detailed interpretation is attempted for the Ba-zeolite harmotome where data were recorded at various temperatures and different amount of water. -Differential scanning calorimetry gave a broad dehydration peak for chabazite (T = 443 K) and a sharp single peak for natrolite ( T = 633 K), whereas three maxima (T = 433, 523 and 673 K) were observed for harmotome.

What does zeolitic water look like?: Modelization by molecular dynamics simulations

“…The global aspect depicted in Figure 15 is similar to the experimental spectra as studied by Fuess et al [83,86], which show a peak around 160 cm-' and the libration band between 480 and 810 cm-I. Moreover, these experimental spectra show that an increase of water content induces a spectrum more similar to that of liquid water [79].…”

“…The corrected spectra eampared to the initial ones show that classical M D simulations do not represent accurately high-frequency movements. However, experimental values for libration of H 2 0 in various zeolitic structures are reported at frequencies between 480 and 630 cm-' [83]. Note here that except for the fact that higher-frequency movements appear for zeolitic water, this latter adopts a far-infrared spectrum shape similar to the liquid water one.…”

Low temperature dynamics of molecular H2O in bassanite, gypsum and cordierite investigated by high resolution incoherent inelastic neutron scattering

“…Furthermore, it is unlikely that such a strong deformation is commensurate with a transition from a dynamically disordered phase into the low temperature form. The influence of the ordering of the H20 molecules in bassanite has a much more pronounced effect on the spectrum than that which has been observed in zeolites (Fuess et al 1986). The narrow widths of most of the observed bands indicate that the molecules are ordered over only a few distinct sites, as a static disorder over many sites generally implies broad bands due to a large number of different potentials felt by the H20 molecules.…”

“…With the advent of more powerful reactor sources and improved spectrometeres, measurements with higher energy resolution have been possible. This allowed the study of the intramolecular dynamics of water molecules in nanoporous solids such as zeolites (Fuess et al 1986;Stuckenschmidt et al 1988). These measurements are based on direct time-of-flight (t.o.f.)…”

An inelastic incoherent neutron scattering study of water in small-pored zeolites and other water-bearing minerals

“…44 We have previously carried out a study on the small-pored zeolite natrolite 11 in which we compare the IINS spectrum with the results of ab initio calculations. In this paper, we reproduce the natrolite spectrum from our previous study 11 ͑which is of higher resolution than that of Fuess 36 and Boutin 40 ͒, in order to compare with the other minerals of this study. As indicated above, apophyllite has been studied before by Boutin 40 but to a lower resolution than this study.…”