The methanol-to-hydrocarbons reaction: insight into the reaction mechanism from [ 12C]benzene and [ 13C]methanol coreactions over zeolite H-beta

• Published in: Journal of catalysis 2004, Vol.221 (1), p.1-10
• Main Authors: Bjørgen, Morten, Olsbye, Unni, Petersen, Dirk, Kolboe, Stein
• Format: Article
• Language: English
• Subjects: Benzene; Beta zeolite; Catalysis; Chemistry; Exact sciences and technology; General and physical chemistry; Heptamethylbenzenium cation; Hydrocarbon pool; Methanol; Methanol-to-hydrocarbons; MTH; Paring reaction; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/S0021-9517(03)00284-7

[ 13C]Methanol and [ 12C]benzene were coreacted over zeolite H-beta at different reaction temperatures, ranging from 210 to 330 °C. The main attention was paid to the material being trapped within the zeolite pores. Hexamethylbenzene and the heptamethylbenzenium cations were easily formed by methylation reactions. The arene methylation reactions leading to hexamethylbenzene and the heptamethylbenzenium cation were much faster than the reactions leading to isotopic scrambling, and the isotopomers 12C 6( 13CH 3) 6 and 12C 6( 13CH 3) 7 + could be synthesized in situ. This achievement was used to elucidate new details in the MTH mechanism. The heptamethylbenzenium cation was the major compound being retained within the pores of the beta zeolite at 250 °C. When the reaction temperature was increased, this species soon vanished and polymethylbenzenes and -naphthalenes became the dominating components. The isotopic distribution observed in both gaseous products and retained material is in excellent agreement with a reaction mechanism where rearrangement of the heptametylbenzenium cation, followed by dealkylation, is the major reaction route for olefin formation in the MTH/MTO reaction over the H-beta zeolite.