An ultraviolet Raman spectroscopic study of coke formation in methanol to hydrocarbons conversion over zeolite H-MFI

The formation of retained hydrocarbons or coke in the conversion of methanol and dimethylether to hydrocarbons over zeolite H-MFI was studied using ultraviolet Raman spectroscopy. Polyolefin, cyclopentadienyl species, and polyaromatic hydrocarbons have been identified among the retained hydrocarbons from the Raman spectra. The results strongly support a reaction mechanism, proposed previously, where cyclopentadienyl species are identified as a key intermediate in the formation of aromatic and polyaromatic hydrocarbons by ring expansion. The spectra also suggest that the polyaromatic hydrocarbons have a chain-like topology, similar to polycenes, rather than a two-dimensional, sheet-like topology, similar to pyrene or coronene.