The conversion of ethylene and propylene absorbed in zeolite H-MFI was studied using UV-Raman spectroscopy. To observe early stage reaction intermediates, an infrared laser was used as a fast heating source. Alkyl substituted naphthalenes and fluorenes, which have been previously suggested as hydrocarbon pool species, were observed regardless of the olefin reagent. Conjugated dienes were formed from propylene but not observed for ethylene at short reaction times. Conventional heating in a furnace was used to force the reaction to completion. For propylene sheet-like polyaromatic hydrocarbons were formed immediately. For ethylene cyclic dienes, conjugated olefins, and ultimately sheet-like polyaromatic hydrocarbons were formed at progressively higher reaction temperatures. The results show that the polyaromatic species implicated as deactivating coke in zeolite catalysts can be formed by conversion of polyenes.
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