W0224

Investigating the Early Stage of Zeolite NaA Crystallization from Gels by In-Situ SWAXS Using Synchrotron Radiation and NMR. Shaoxu Han¹, Robert W. Broach², Haydn Chen¹ and R. Lyle Patton², ¹Dept. of Materials Science & Engineering, University of Illinois, Urbana, IL 61801, ²UOP LLC, Des Plaines, IL 60017 USA

Simultaneous in-situ small- and wide-angle X-ray scattering (SWAXS) using synchrotron radiation and in-situ NMR were employed to investigate the crystallization process of zeolite NaA from gels. The SWAXS experiments were performed at beamline 8.2 of the SRS, Daresbury Laboratory, U.K. The hydrothermal synthesis of zeolite NaA was carried out in a specially-designed reaction cell. The reaction cell can be rotated and heated up to 125 [ring]C. With the high-brilliance synchrotron radiation, a complete set of SWAXS pattern was collected every two minutes with two position sensitive detectors.

Gel transformations occurring during the aging period were monitored by SAXS while crystallization of zeolite NaA was monitored by WAXS. During aging the scattering intensity near low Q grew slowly as a function of time, indicating the reorganization of aggregates and the formation of large aggregates. When heating started, the intensity at low Q increased quickly and reached the maximum in eight minutes. This showed that large aggregates were forming at the early stage of heating and they might continue to grow at the even lower Q region not accessible in this experiment before crystallization occurred. The slopes calculated from the log-log plot from the SAXS data revealed that the amorphous precursor exhibited surface fractal behavior (1.8<Ds<2.5 between Log Q values -1.8 to -1.5) and the surface structure changed from smooth to rough. WAXS data showed that for the first 30 minutes of heating no peaks were detected for the crystalline NaA. Around 40 minute after heating, small peaks from the crystalline material started to appear. The diffraction intensity reached the maximum within two hours after heating, indicating that crystallization process was completed, which was faster than expected. Crystallization rate is determined based upon integrated intensity analysis. Solution NMR was performed at research center at UOP LLC, and no detectable Si species were found in solution at any time during the crystallization process.