Conversion of methanol to hydrocarbons: Hints to rational catalyst design from fundamental mechanistic studies on H-ZSM-5

In this study, the mechanism of the methanol-to-hydrocarbons (MTH) reaction over H-ZSM-5, which is the archetype MTH catalyst, has been pursued. From isotopic labeling experiments, it is demonstrated that the reaction scheme for alkene formation from methanol over H-ZSM-5 is essentially different from those previously drawn for H-beta and H-SAPO-34. In addition to a modified hydrocarbon pool mechanism, wherein ethene is formed from the lower methylbenzenes, a parallel C3+ alkene methylation/cracking cycle is operative. The results showing that ethene and propene are formed through different catalytic cycles, are of utmost importance for understanding and possibly controlling the ethene/propene selectivity in methanol-to-propene catalysis.