| Abstract
| - The dynamics and stoichiometry of thiophene adsorption and of rearrangements of thiophene-derivedadsorbed species in O2, He, H2, and C3H8 carriers were measured using chromatographic methods andmass spectrometry on H-ZSM5 and H-Y zeolites. Thiophene adsorption obeyed Langmuir isotherms onboth zeolites. Adsorption uptakes were 1.7 and 2.8 thiophene/Al at 363 K on H-ZSM5 and H-Y zeolites,respectively, after removal of physisorbed thiophene. These stoichiometries differed for these two zeolitestructures but did not depend on their Al content (Si/Al = 13−85). Adsorption from a thiophene−toluenemixture showed thiophene selectivities (∼10) greater than expected from van der Waals interactions.These adsorption stoichiometries, without contributions from physisorption, and the color changes detectedindicate that thiophene adsorption occurs concurrently with oligomerization on acidic OH groups and thatoligomer size depends on spatial constraints within channels. Thiophene oligomers decompose at ∼534K during subsequent thermal treatment to form molecular thiophene with all carriers, leaving behindunsaturated thiophene-derived species with a 0.9−1.1 thiophene/Al stoichiometry, confirming the specificityof OH groups and the oligomeric nature of bound thiophene during adsorption at 363 K. With He, H2, andC3H8, residual thiophene-derived species desorb as stable fragments, such as H2S, ethene, propene, arenes,and heavier organosulfur compounds (methylthiophene and benzothiophene) during thermal treatment;they also form unsaturated organic deposits that cannot desorb without hydrogenation events. H2 andC3H8 remove larger amounts of adsorbed species as unreacted thiophene than He, suggesting thatdehydrogenation reactions are inhibited or reversed by a hydrogen source. C3H8 removes a larger fractionof thiophene-derived intermediates as hydrocarbons and organosulfur compounds than H2 or He; thus,hydrogen atoms formed during C3H8 dehydrogenation are more effective in the removal of unsaturateddeposits than those formed from H2. Thiophene-derived adsorbed species are completely removed onlywith O2-containing streams at 873 K, a process that fully recovers initial adsorption capacities. This studyprovides a rigorous assessment of the nature and specificity of thiophene adsorption processes on acidicOH groups and of the identity and removal pathways of adsorbed species in various reactive environments.
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