Tracking Lattice Distortion Induced by Defects and Framework Tin in Beta Zeotypes

Abstract

The use of powder X-ray diffraction (PXRD) coupled with lattice parameter refinement is used to investigate the crystal structure of Sn-Beta materials. A newly developed semiempirical PXRD model with a reduced tetragonal unit cell is applied to obtain the characteristic crystallographic features. There is a robust correlation between lattice parameters and the concentration of tin and defects for materials prepared via hydrothermal (HT) and postsynthetic (PT) methods. With tin incorporation, PT Sn-Beta samples, which possess a more defective structure, exhibit an extended interlayer distance in the stacking sequence and expansion of the translation symmetry within the layers, leading to larger unit cell dimensions. In contrast, HT Sn-Beta samples, having fewer defects, show a minimal effect of tin site density on the unit cell volume, whereas lattice distortion is directly correlated to the framework tin density. Furthermore, density functional theory (DFT) studies support an identical trend of lattice distortion following the monoisomorphous substitution of T sites from silicon to tin. These findings highlight that PXRD can serve as a rapid and straightforward characterization method to evaluate both framework defects and heteroatom density, offering a novel approach to monitor structural changes and the possibility to evaluate the catalytic properties of heteroatom-incorporated zeotypes.

Deactivation and Reductive Regeneration of Sn-Beta for Liquid-Phase Biomass Conversion

“…These findings imply certain changes in the crystal structure of Sn-Beta during the reaction that are associated with a crystal lattice distortion (different c/a ratios). As recently reported, XRD analysis suggests that a decrease in c/a ratio is linked with a lower concentration of tin in the framework and/or silanol defects . This corroborates the findings from FTIR (Table ).…”

“…As recently reported, XRD analysis suggests that a decrease in c/a ratio is linked with a lower concentration of tin in the framework and/or silanol defects. 58 This corroborates the findings from FTIR (Table 2). In addition to structural changes in the zeolitic framework, we observed differences among the fresh and regenerated catalysts with respect to SnO 2 .…”