HYDROTHERMAL CONVERSION OF ZEOLITES; AN IN-SITU TIME RESOLVED SYNCHROTRON X-RAY POWDER DIFFRACTION STUDY. P. Norby, Chemistry Department, Brookhaven National Laboratory

Using hydrothermal conversion of zeolites, new materials not obtainable by conventional synthesis may be obtained. By using in-situ synchrotron powder diffraction combined with ex-situ SEM, hydrothermal conversion of zeolite Na-LTA was followed. Using the equipment developed, hydrothermal conditions up to 260deg.C can be obtained using an applied pressure of 45 atm. Hydrothermal conversion with aqueous solutions of LiCl and AgNO₃ were performed. The conversion zeolite LTA --> zeolite Li-A(BW) was followed in details using in-situ powder diffraction at temperatures from 200-260deg.C. Also, partially converted samples were prepared in-situ on the diffractometer, and investigated using Scanning Electron Microscopy. While the transformation process proceeds via dissolution, the zeolite-LTA crystallites serve as nucleation centers for zeolite Li-A(BW).

A Translating Image Plate System (TIPS) has been developed especially for time- temperature- and wavelength-dependent powder diffraction experiments. We are currently studying solid-solid, solid-gas and solid-liquid phase reactions with special emphasis on hydrothermal and solid state syntheses, ion exchange, phase transformations and chemical reactions. Information concerning e.g. kinetics of crystallization, transformation and chemical reactions, development of crystallite size, and occurrence and identification of intermediate phases have been obtained.

All reactions and syntheses are performed in .5-1mm quartz glass capillaries heated using a hot air stream. Hydrothermal conditions up to 260deg.C (45 atm.) are obtained by applying an external gas pressure to the reaction mixture.

This work was supported under contract DE-AC02-76CH00016 with the US Department of Energy by its Division of Chemical Sciences, Office of Basic Energy Sciences and by the Danish Natural Science Research Council.