Methanol Conversion to Hydrocarbons over Zeolite H-ZSM-5: Investigation of the Role of CO and Ketene in the Formation of the Initial CC Bond

• Published in: Journal of catalysis 1993-08, Vol.142 (2), p.602-616
• Main Authors: Hutchings, G.J., Hunter, R., Johnston, P., Vanrensburg, L.J.
• Format: Article
• Language: English
• Subjects: 01 COAL, LIGNITE, AND PEAT; 010408 - Coal, Lignite, & Peat- C1 Processes- (1987-); 10 SYNTHETIC FUELS; 100200 - Synthetic Fuels- Production- (1990-); 400201 - Chemical & Physicochemical Properties; ALCOHOLS; ALKENES; CARBON 13; CARBON COMPOUNDS; CARBON ISOTOPES; CARBON MONOXIDE; CARBON OXIDES; CATALYSIS; CATALYSTS; CATALYTIC EFFECTS; Catalytic reactions; CHALCOGENIDES; CHEMICAL PREPARATION; Chemistry; CONVERSION; DEUTERIUM; ELEMENTS; ETHYLENE; EVEN-ODD NUCLEI; Exact sciences and technology; General and physical chemistry; HETEROGENEOUS CATALYSIS; HYDROCARBONS; HYDROGEN; HYDROGEN ISOTOPES; HYDROXY COMPOUNDS; INORGANIC ION EXCHANGERS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ION EXCHANGE MATERIALS; ISOTOPES; KETENES; LABELLED COMPOUNDS; LIGHT NUCLEI; MATERIALS; METHANOL; MINERALS; NONMETALS; NUCLEI; ODD-ODD NUCLEI; ORGANIC COMPOUNDS; ORGANIC OXYGEN COMPOUNDS; OXIDES; OXYGEN COMPOUNDS; REACTION INTERMEDIATES; SILICATE MINERALS; STABLE ISOTOPES; SYNTHESIS; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; ZEOLITES
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1006/jcat.1993.1234

Mechanistic studies concerning the formation of the initial carboncarbon bond in the methanol conversion reaction over zeolite H-ZSM-5 are described and discussed. In particular, the possible roles of CO as a reaction intermediate or as a catalyst, via the formation of ketene, are evaluated. Experiments using 13CH 3OH/ 12CO reactant mixtures demonstrate that no CO is incorporated into ethene, the primary product of this reaction. In addition, CO is found to have no significant effect on the induction period for this reaction. Model experiments for the methylation of ketene by reaction with Me 2SO 4 and Me 3O +SbCl − 6 did not provide evidence for methylation of ketene on either of the C atoms, and from the products observed it is apparent that ketene acts only as an acylating agent in the normal way. Experiments using aluminium silica compounds as models for the active site in the zeolite are described and discussed. Hydrogen/deuterium exchange experiments indicate that a common intermediate exists that can lead to the eventual formation of CH 3OCH 3, CH 4, and C 2H 4. Coreaction of CD 3OCD 3 and CH 3OCH 3 indicates that at least two intermediates are required for the formation of the ethene primary product. The results of this study indicate that CO and CH 2CO play no significant mechanistic role in the formation of the primary products of methanol conversion. A mechanism consistent with the experimental evidence available involving a surface bonded methoxy group is proposed and discussed.