Conversion of Methanol into Hydrocarbons over Zeolite H-ZSM-5:  Ethene Formation Is Mechanistically Separated from the Formation of Higher Alkenes

The widely debated reaction mechanism for the conversion of methanol to hydrocarbons over acidic zeolite H-ZSM-5 has been investigated using isotopic labeling. The mechanistic findings for H-ZSM-5 are clearly different from those previously described at a detailed level for H-beta and H-SAPO-34 catalysts. On the basis of the current set of data, we can state that, for H-ZSM-5, ethene appears to be formed exclusively from the xylenes and trimethylbenzenes. Moreover, propene and higher alkenes are to a significant extent formed from alkene methylations and interconversions. This implies that ethene formation is mechanistically separated from the formation of higher alkenes, an insight of utmost importance for understanding and possibly controlling the ethene/propene selectivity in methanol-to-alkenes catalysis.