H-1-NMR STUDIES OF THE ADSORPTION OF WATER ON SILICALITE

A study has been made of silicalite samples with a specific surface ar ea (by the BET met:hod) of S=350 m(2) g(-1) which were synthesized on the basis of fumed silica and did not contain aluminum. H-1 NMR spectr oscopy is used to determine the value of the chemical shift of the ads orbed water molecules and to characterize the adsorbed water layers. I t has been found that in the case of both water vapor adsorption and w ater adsorption from aqueous suspensions, the volume of silicalite por es occupied by adsorbed water molecules is considerably smaller than t he total volume of the pores. The chemical shift of water molecules on the silicalite surface depends on temperature and varies from 4.5 ppm at 330 K to 5.6 ppm at 220 K. The high chemical shift values are attr ibuted to clustering of water molecules in the adsorbent pores, and to the fact that each molecule of the clusters participates simultaneous ly in the formation of more than three hydrogen bonds. (C) 1998 Elsevi er Science B.V. All rights reserved.