Understanding of the key factors responsible for stannosilicate crystallization chemistry: Operando XAS investigation

Recently, we reported on a breakthrough approach to engineer heteroatom-containing zeolites, i.e., a new bottom-up approach called Electro-Assisted Synthesis (EAS) [3,4]. EAS combines in-situ anodic oxidation of a desired metal during a hydrothermal (often) siliceous zeolite synthesis reaction. EAS is a versatile tool that has already proved its efficiency for the creation of Sn-CHA, -MFI and -BEA zeolites with record tin contents; next to being explored as well for Zn [5], Al and Ti heteroatoms. While the synthesis method is proven to be highly generic (e.g., between variety of metal and zeolite frameworks), the understanding of its efficiency is still missing. From conventional characterization techniques, we were able to underline 3 key parameters for the EAS success: i) concentration of heteroatoms, ii) timing of the release and iii) reactive species formation; while only first two are demonstrated so far. We believe that the key aspect responsible for the outstanding material formation can be proven with XAS operando technique.
For that, we built and successfully tested a dedicated operando cell (Figure 1, Left and Center), which is capable of running both hydrothermal and electrochemical reaction, while subjected to a synchrotron X-ray radiation (i.e., XAS). The initial data were collected at SAMBA beamline of Soleil synchrotron (Figure 1, Right), where we could obtain the essentials on the oxidation state and concentration of Sn particles. Due to the time limitation of the beamtime (48 hours) and long synthesis times, additional datasets correlated with conditions, for which PXRD, ICP AES and FT-IR were collected, are required for complete understanding. Therefore, here, we propose a systematic investigation of Sn-MFI crystallization by in situ and ex situ X-ray absorption spectroscopy at Sn K-edge (XANES and EXAFS).