Hydrocarbon formation from methanol and dimethyl ether using WO3/Al2O3 and H-ZSM-5 catalysts. A mechanistic investigation using model reagents

Abstract

The methanol conversion catalysts H-ZSM-5 and 10% WO₃/Al₂O₃ show significant differences in their activities as well as product selectivities towards a range of reagents Me—X [X =—OH, —OMe, —I, —OSO₃Me, —OP(OMe)₂O]. WO₃/Al₂O₃ is typically two orders of magnitude less active and gives significant yields of methane and hydrogen compared to the zeolite catalyst. Formation of C₂₊ hydrocarbons over WO₃/Al₂O₃ with Me₂SO₄ and (MeO)₃PO provides evidence that the trimethyloxonium ion is an unlikely intermediate in the methanol to hydrocarbon conversion reaction, since these reagents cannot form this type of intermediate. Reactions in the presence of added hydrogen do not show significant differences in the product selectivities, particularly methane, indicating that the methane does not originate from reaction of an intermediate, e.g. methylene carbene, with molecular hydrogen. Significant differences in catalyst behaviour in the presence of added NO and O₂ indicate different reaction mechanisms for initial C—C bond formation with both catalysts.