New insight in the template decomposition process of large zeolite ZSM-5 crystals: an in situ UV-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.