In Situ Investigation of Si-TPA-MFI Crystallization Using (Ultra-) Small- and Wide-Angle X-ray Scattering

Abstract

The formation of precursors and the growth and aggregation of silicalite-1 crystals using tetrapropylammonium as a template (Si-TPA-MFI) has been studied in situ using X-ray scattering techniques. Simultaneous smallangle and wide-angle X-ray scattering (respectively SAXS and WAXS) experiments using synchrotron light showed that the formation of amorphous colloidal aggregates in water clear synthesis mixtures was dependent on the alkalinity of the solutions. In situ time-resolved ultra-small-angle X-ray scattering (USAXS) showed the form factor oscillations of the growing crystals. Fitting of the USAXS patterns to the scattering pattern of spherical particles having a normal particle size distribution showed a linear growth of the average crystal diameter, which was approximately the same for both alkalinities studied. The final size of the crystals was highest for the synthesis mixture having the highest alkalinity, which can be explained in terms of number of viable nuclei formed. At the end of the linear growth the crystals form aggregates corresponding with a diffusion limited aggregation process (mass fractal dimension of 1.8).

An Overview of Zeolite, Zeotype and Mesoporous Solids Chemistry: Design, Synthesis and Catalytic Properties

“…Long-range order is attained in a consecutive layer-by-layer zeolite growth step. This proposed formation mechanism is in agreement with results of an in situ SAXS and WAXS study by de Moor et al [15] of the same system. Their results show the initial formation of colloidal amorphous aggregates, which are not organized further in a secondary aggregation step, but instead, redissolve and act as a source of nutrients for the growing crystallites.…”

“…The aforementioned studies involve in situ IR, 29 Si NMR and X-ray scattering techniques, [13][14][15]17] although only the gel stage of the zeolite formation process was covered in these cases. The next step is the study of the crystallization process for these microporous materials, and indeed several research groups have reported such in situ investigations.…”

“…The next step is the study of the crystallization process for these microporous materials, and indeed several research groups have reported such in situ investigations. [15,22,23] Unfortunately, only one analytical technique was used in each of these studies, which makes it difficult to obtain information on all aspects of the crystal growth process. Very recently, Grandjean et al reported the combination of multiple time-resolved in situ techniques, namely SAXS-WAXS, UV-vis, Raman and XAS, for probing the crystallization of a cobalt-modified aluminophosphate material, Co-APO-5.…”

Dynamic Powder Crystallography With Synchrotron X-Ray Sources

“…In their current configurations, neither of the above cell types (capillary or autoclave) is particularly suited to study the early stages of FeS nucleation reactions. Rather, other synchrotron-based techniques such as simultaneous SAXS-WAXS (small-and wide-angle X-ray scattering, respectively) experiments may make a contribution to our understanding of these reactions (de Moor et al 1997, Shaw et al 2000c.…”

Hydrothermal Stability of Meso-microporous Composites and Their Catalytic Cracking Performance

“…85%) have the size of 11.9 nm beside a small amount of larger sol particles with the size of 100 nm generated from the rapid hydrolysis and condensation processes of TEOS and Al(i-OPr) 3 in alkaline solution. de Moor et al [22,23] observed two types of precursor particles (2.8 nm sized primary units and ~10 nm aggregates) in MFI zeolite synthesis systems by small-angle X-ray scattering. Based on these results, sol particles can be thought reasonably to be aggregates of zeolite primary units.…”