Conversion of [ 14C]methanol and propane mixtures with H-ZSM-5

One of the major discoveries in zeolite catalysis was the conversion of methanol to gasoline using H-ZSM-5 catalysts. While there have been many mechanistic studies, the reaction pathway and the C{sub 1} species involved in the reaction remain uncertain. The proposed mechanisms may be classified into three groups based upon the required intermediate: (a) mechanisms utilizing carbene (:CH{sub 2}), (b) mechanisms utilizing cations (e.g., CH{sub 3}{sup +}), and (c) mechanisms utilizing trimethyloxonium ions ((CH{sub 3}){sub 3}O{sup +}) or similar oxygen-containing species. Preliminary {sup 14}C tracer studies provided evidence that was consistent with the oxonium ion intermediate. Refinements in the {sup 14}C analytical procedures showed that the {sup 14}C added in propanol had completely scrambled with the methanol carbon and the data could therefore not define the intermediate species. Considering the importance of experiments with the methanol-propane mixture to an understanding of the methanol to gasoline conversion, the author has carried out studies using {sup 14}CH{sub 3}OH and unlabeled propane.