New insight in the template decomposition process of large zeolite ZSM-5 crystals: an in situUV-Vis/fluorescence micro-spectroscopy study

Abstract

A combination of in situ UV-Vis and confocal fluorescence micro-spectroscopy was used to study the template decomposition process in large zeolite ZSM-5 crystals. Correlation of polarized light dependent UV-Vis absorption spectra with confocal fluorescence emission spectra in the 400-750 nm region allowed extracting localized information on the nature and amount of chemical species formed upon detemplation at the single particle level. It has been found by means of polarized light dependent UV-Vis absorption measurements that the progressive growth of molecules follows the orientation of the straight channels of ZSM-5 crystals. Oligomerizing template derivatives lead to the subsequent build-up of methyl-substituted benzenium cations and more extended coke-like species, which are thermally stable up to ∼740 K. Complementary confocal fluorescence emission spectra showed nearly equal distribution of these molecules within the entire volume of the thermally treated zeolite crystals. The strongest emission bands were appearing in the orange/red part of the visible spectrum, confirming the presence of large polyaromatic molecules.

In-situ imaging of reacting single-particle zeolites by non-linear optical microscopy

“…For the complete removal of the SDA, this heating process is continued typically continued for days to weeks, to ensure complete removal of the SDA material and all other materials formed during the calcination process. These results are similar to that of Karwacki et al [6][7][8], with the observation of the presence of pyramidal subunits. In addition, instead of simply observing changes in the material, we can use multichannel spectral information to assist in the understanding of the chemical reactions and the spatial distribution of these reactions with high spatial resolution.…”

“…For example, utilizing large single crystals of MFI (50 × 200 × 50 µm 3 ), Karwacki, et al noted during the heating process using fluorescence microscopy that crystals darkened (due to the formation of decomposition products) in a spatially non-uniform matter. This non-uniform darkening was thought to be due to discontinuities in the crystalline structure, or intergrowths [6][7][8]. The crystalline structure, including the subunits of the single-body zeolites are important for understanding chemical activity as it is observed that different subunits and the interfaces between the subunits respond differently to thermal treatments.…”

Diagnosing the Internal Architecture of Zeolite Ferrierite

“…Our group has been developing CFM under in situ conditions to elucidate the internal crystallographic intergrowth structure by monitoring fluorescent species during the template removal process at high temperature for AFI, CHA, and MFI frameworks . In the present work we applied this same method to template‐containing crystals of purely siliceous FER ( 1 ), by heating them under a N 2 atmosphere to 600 °C.…”

Effect of Feedstock and Catalyst Impurities on the Methanol‐to‐Olefin Reaction over H‐SAPO‐34

“…In previous studies, our group has provided experimental evidence for the formation of distinct zeolite‐occluded hydrocarbon species upon detemplation 46, 47. Karwacki et al.…”

“…studied the template decomposition process in large ZSM‐5 crystals by using in situ fluorescence microscopy and reported increasingly larger (conjugated) aromatic molecules with increasing temperatures. These larger coke‐like derivatives are more resistant to thermal decomposition 46. Qian et al.…”