1H NMR studies of the adsorption of water on silicalite

Water Dynamics on the Surface of MCM-41 via 2H Double Quantum Filtered NMR and Relaxation Measurements

“…(2) 〉 ) SD 00 (2) (θ), where axial symmetry of the adsorption interaction and site distribution are assumed and the third term in eq 9 can be deduced from the term 〈D 00 (4) 〉 ) 〈D 00 (4) 〉 m D 00 (4) (θ). To evaluate 〈D 00 (4) 〉 in terms of S, a specific distribution for the cone model is needed. For an isotropic distribution with a cone angle of b, Brainard and Szabo 21 obtained S ) 1/2 cos b(1 + cos b).…”

Structure of Hydrogen Bonds and 1H NMR Spectra of Water at the Interface of Oxides

“…Fumed silica (Aerosil A-300, 99.5% purity and specific surface area ( S BET ) approximately 300 m 2 g -1 ) and fumed silica/alumina (SA) (99.5% purity, 3 (SA 3 ) and 23 (SA 23 ) wt % Al 2 O 3 , and S BET ≈ 180 and 170 m 2 g -1 , respectively) were produced at PU “Chlorovinyl” (Kalush, Ukraine). The S BET values were measured using adsorption of nitrogen at ≈78 K. Two studied silicalite samples ( S BET ≈ 350 m 2 g -1 ) with a ZSM-5-like structure and different crystallinities (100 and 66%, estimated from the XRD data) as well as their syntheses were described in detail elsewhere . Commercial rutile ( S BET ≈ 14 m 2 g -1 ) covered by a small amount (2−4 wt %) of silica and alumina was studied as received.…”

The Influence of Aluminium Concentration on the Hydration of ZSM-5-Type Zeolites in Aqueous Suspensions

“…One more feature of the studied type of microporous materials manifests itself in the fact that the dependency curves DG = f(C) over the whole range of variation in the concentration of unfrozen water for aqueous suspensions of adsorbents are located above the corresponding curves for hydrated powders, while in the case of non-porous and mesoporous adsorbents the reverse is true . As has been shown by Turov and Leboda (1999), the increase in DG in going from an aqueous to air medium is caused by the fact that in addition to the adsorbent/water interface there appears to be a water/air interface which makes an additional contribution to the measured value of DG. The established regularity is probably due to the fact that in hydrated powders the formation of a new water/air interface does not take place.…”

“…This freezing results in a decrease in size of the liquid water clusters adsorbed in the pores. The chemical shift value for water in polyassociates is determined by the number of hydrogen bonds (n) in whose formation every molecule of water participates simultaneously Turov and Leboda 1999). With decreasing temperature, the number of such bonds increases at the expense of a retardation in the molecular motion and, as a result, a displacement of the signal for adsorbed water into the region of weak magnetic fields (an increase in the chemical shift) is observed.…”

“…Our measurements were undertaken using the 1 H NMR spectral technique in conjunction with a method based on the freezing-out of a liquid phase (Turov and Barvinchenko 1997;Turov and Leboda 1999;Gun'ko et al 1995Gun'ko et al , 1997. This technique enables the measurement of the concentrations of water adsorbed on the surface and allows the calculation of the values of the free surface energy of the adsorbent at the adsorbent/water interface.…”