The Catalytic Conversion of Thiophenes over Large H-ZSM-5 Crystals: An X-Ray, UV/Vis, and Fluorescence Microspectroscopic Study

Abstract

X-ray absorption, UV/Vis, and fluorescence microspectroscopy have been used to characterize the catalytic conversion of thiophene derivatives within the micropores of an individual H-ZSM-5 zeolite crystal. Space resolved information into the Si/Al ratios and sulfur content was provided by X-ray absorption microspectroscopy. X-ray absorption near edge spectroscopy spectral information and modeling indicated the presence of a sulfur atom, in close proximity of two oxygen atoms, that is at approximately 2.5 angstrom. Space-resolved spectroscopic measurements provided experimental evidence for the formation of conjugated carbocationic reaction intermediates by opening of the thiophene ring. The molecular alignment of reaction products within the straight pores of the individual H-ZSM-5 zeolite crystals was observed with polarized light UV/Vis microspectroscopy. In addition, confocal fluorescence microscopy revealed the 3D distribution of different reaction products and demonstrated the influence of the H-ZSM-5 crystal's intergrowth structure and its related molecular diffusion barriers.